Table of contents :

• Erythropoiesis stimulating agents
• Procoagulants
• Anticoagulants
• Antithrombotics
• Thrombolytics / fibrinolytics
• Antithrombolytics
• Antiplatelet drugs
• Anti-dyslipidemia xenobiotics
• Anti-hyperuricemia

In many ways, erythrocytes would make an ideal agent for drug delivery. They are the most abundant cellular constituent in blood, and on average travel hundreds of kilometres in the vasculature during their lifespan (100–120 days). If they could be converted into carriers, they could, in theory, prolong the circulation and improve the bioavailability of drugs that act in the bloodstream. Loading therapeutic agents into erythrocytes is of limited value, as many drugs diffuse poorly across the erythrocyte membrane. However, coupling agents to the erythrocyte surface could overcome this problem.

Hematopoiesis-stimulating agents :

Erythropoiesis stimulating agents (ESA) :

EPO-R agonists

continuous erythropoietin recepor activator (CERA) : integration of a single 30 kDa polymer chain into erythropoetin to increase elimination half-life in man to about 130 h => every 3 weeks. This methoxy-polyethylene glycol polymer chain is integrated through amide bonds between the N-terminal amino group or the e-amino group of lysine (predominantly lysine-52 or lysine-45), with a single succinimidyl butanoic acid linker. (Haselbeck A, Bailon P, Pahlke W, et al. The discovery and characterization of CERA, an innovative agent for the treatment of anemia. Blood 2002;100;227A(abstr 857); Provenzano R, Besarab A, Macdougall IC, et al. for the BA16528 study group. CERA (continuous erythropoietin receptor activator) administered up to once every 3 weeks corrects anemia in patients with chronic kidney disease not on dialysis. J Am Soc Nephrol 2004;15;544A; Localtelli F, Villa G, Arias M, et al, for the BA16286 study group. CERA (continuous erythropoietin receptor activator) maintains hemoglobin levels in dialysis patients when administered subcutaneously up to once every 4 weeks. J Am Soc Nephrol 2004;15;543A; Dmoszynska A, Kloczko J, Rokicka M, et al. CERA (continuous erythropoietin receptor activator) in patients with multiple myeloma: an exploratory phase I-II dose escalation study. J Clin Oncol 2004;22 (suppl.15):14S; ^ref)

synthetic erythropoiesis protein (SEP) : 2 covalently attached polymer moieties^ref

erythropoietin fusion protein (EFP) of 2 complete human EPO domains linked by a 17-aminoacid flexible peptide; increased rRBC production within 7 days at a dose at which epoetin was ineffective^ref

methoxy polyethylene glycol-epoetin b (Mircera^®; source : Roche). In correction, the primary endpoint was the Hb response rate during the correction period. The criteria for response was Hb increase>1 g/dL above baseline and Hb >11 g/dL during correction period without red blood cell (RBC) transfusion.

• the first study (AMICUS) was designed to evaluate anaemia correction with Roche's long-acting ESA (iv) once every 2 weeks in naïve patients with CKD on dialysis vs. epoetin.4
• the second study (ARCTOS) was designed to evaluate anaemia correction with Roche's long-acting ESA (sc) once every 2 weeks in naïve patients with CKD not on dialysis vs. darbepoetin alfa.5

In maintenance, the primary endpoint was the change in Hb concentration between baseline and the evaluation period:

• the first study (MAXIMA) was designed to evaluate Roche's long-acting ESA (iv) in the maintenance of Hb levels in CKD patients on dialysis previously maintained on iv epoetin. Intravenous epoetin was dosed up to three times weekly compared to Roche's long-acting ESA dosed once every two weeks or once every four weeks
• the second study (PROTOS) was designed to evaluate Roche's long-acting ESA (sc) in the maintenance of Hb levels in CKD patients on dialysis previously maintained on sc epoetin. Subcutaneous epoetin was administered up to 3 times weekly, compared to Roche's long-acting ESA dosed either once every two weeks or once every four weeks
• the third study (STRIATA) was designed to evaluate Roche's long-acting ESA (iv) in the maintenance of Hb levels in CKD patients on dialysis previously maintained on iv darbepoetin alfa. Darbepoetin alfa was dosed once a week or once every two weeks compared to Roche's long-acting ESA dosed once every 2 weeks
• the fourth study (RUBRA) was designed to evaluate Roche's long-acting ESA (sc or iv) in a pre-filled syringe in the maintenance of Hb levels in patients on dialysis previously maintained on epoetin. Epoetin was administered up to three times weekly compared to Roche's long-acting ESA administered once every 2 weeks

erythropoietin mimetic peptides (structurally unrelated to EPO)

erythropoietin-mimetic peptide 1 was a cyclic oligopeptide^{ref1, ref2}

Hematide^TM (source : Affymax) (Woodburn K, Fan Q, Holmen CP, et al. Preclinical evaluation of Hematide, a novel eryhtropoiesis stimulating agent that corrects anemia induced by partial nephrectomy and erythropoietin-specific antibodies in rats. Stockhlom:European Hematology Association meeting, 2005) is an investigational PEGylated synthetic peptide that stimulates erythropoiesis in animal models and is being developed for the treatment of anemia associated with chronic renal failure and cancer. A study evaluated the safety and pharmacodynamics of single, intravenous doses (0.025, 0.05, and 0.1 mg/kg) of Hematide in 28 healthy male volunteers. All doses of Hematide were well tolerated, with safety profiles similar to that of placebo. Hematide showed a dose- dependent increase in reticulocytes. The 0.1 mg/kg dose was associated with a statistically significant increase in hemoglobin (Hgb) from baseline compared to the placebo group (1.36 +/- 0.39 vs. 0.39 +/- 0.38 g/dL; p < 0.0001) that was sustained for > 1 month. These results support Phase 2 studies in patients with anemia associated with chronic kidney disease or cancer, and suggest that Hematide administered as infrequently as once a month may result in a sustained elevation of Hgb levels^ref

small-molecule nonpeptides : 8 copies of N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester held together by a central core^ref

haemopoietic cell phosphatase inhibitors extend the phosphorylation of JAK2 and STAT5^{ref1, ref2}

HIF-1a stabilisers : moderate genetic overxpression of HIF causes premature mortality related to cerebrovascular events and peripheral thrombosis^ref

HIF-1a prolyl 4-hydroxylase (HPH) inhibitor^{ref1, ref2} (Urquilla P, Fong A, Oksanen S, et al. Upregulation of endogenous EPO in healthy subjects by ihibition of HIF-PH. J Am Soc Nephrol 2004;14;546A; Wiecek A, Piecha G, Ignacy W, et al. Pharmacological stabilization of HIF increases hemoglobin concentration in anemic patients with chronic kidney disease. Nephrol Dial Transplant 2005;20(suppl.6) v195))

• thrombopoiesis-stimulating agents : TPO-R agonists

• chemical styptic : one which arrests hemorrhage by causing coagulation through chemical action.
• biodegradable nanofiber fibrinogen bandage
• protamine sulfate (protamine sulfate^®)

Side effect(s) : acute systemic arterial hypotension => cardiovascular collapse, bradycardia, pulmonary arterial hypertension, dyspnoea, transient flushing, anaphylaxis and anaphylactoid reactions, urticaria, angioedema, acute pulmonary oedema
Precaution(s) : check for hypersensitivity to protamine before administration. Consider the risk of hypersensitivity to protamine in patients with known sensitivity to fish, vasectomised or infertile males, and in patients who have received protamine-containing insulin or previous protamine therapy. Resuscitative equipment and the facilities to manage anaphylaxis should be readily available. Avoid rapid injection as severe cardiovascular collapse may occur. Protamine is a weak anticoagulant and overdosage may theoretically result in bleeding.
• mechanical styptic : one which acts by causing coagulation mechanically, as a pledget of cotton
• commercially available materials commonly used in non-adhering wound dressing :
• alginate : a salt of alginic acid (a hydrophilic colloidal carbohydrate extracted with dilute alkali from species of brown seaweed of the class Phaeophyceae (brown algae); used as a tablet binder and emulsifying agent), which is extracted from marine kelp. Calcium, sodium (algin : sodium alginate, a purified carbohydrate (sodium mannuronate) extracted from brown algae species and used as a stabilizing colloid in numerous pharmaceuticals, cosmetics, and foods), and ammonium alginates have been used as foam, clot, or gauze for absorbable surgical dressings. Soluble alginates, such as sodium, potassium, and magnesium alginates, form a viscous sol which can be changed into a gel by a chemical reaction with compounds such as calcium sulfate, a property which makes them useful as materials for taking dental impressions.
• Adaptic^® (source : Johnson & Johnson) : a unique knitted open mesh fabric coated with petroleum emulsion
• Trofoprocess^®
• Keratoprocess^® (source : Pharmacia)
• hemicellulose (Veloderm^®)
• sodium hyaluronate (Connettivina^®)
• estherified hyaluronate (Transprocess^®)
• vascular styptic : one which acts by producing contraction of injured or divided blood vessels of small calibe

• oral anticoagulants (PO) : g-glutamyl carboxylase inhibitors

D-warfarin has biliary clearance, while L-warfarin has renal clearance. They bind albumin in plasma. The rate-limiting step in biotransformation of warfarin to its 7-hydroxylated metabolite is Cyp2c29^ref
Indications :
• class I :
• chronic atrial fibrillation (INR = 2-3)
• mechanical valve prostheses (INR = 2.5-3.5)
• biological valve prostheses (INR = 2-3 for 3 months)
• therapy, primary and secondary prevention of DVT in patient with high risk (fracture, hip prostheses, protein C or S, ATIII deficiency) (INR = 2-3 for 3-6 months)
• recurrent arterial thromboembolism (INR = 2-4.5)
• class IIa
• acute myocardial infarction (INR = 2-3)
• thrombosis (INR = 2-3)
• class IIb
Interactions :
• slower removal from the body
• amiodarone
• cimetidine
• metronidazole
• omeprazole
• zafirlukast
• thrombocytopenia => increased bleeding risk
• anabolic steroids
• androgens
• azole antifungals
• antithyroid agents
• aspirin or other salicylates
• some cephalosporines reduce Gla
• cinchophen
• clofibrate
• danazol
• dextrothyroxine
• diflunisal or
• disulfiram
• fluvoxamine
• lepirudin
• paroxetine
• propafenone
• quinidine
• sertraline
• sulfapyridine
• sulfasalazine
• thyroid hormones
• ticlopidine
• zileuton
• medicines together with anticoagulants may increase the chance of bleeding
• carbenicillin by injection
• dipyridamol
• divalproex
• moxalactam
• pentoxifylline
• plicamycin
• sulfinpyrazone
• thrombolytic agents
• ticarcillin
• valproic acid
• faster removal from the body
• plasma proteins binders : acute administration of phenylbutazone, sulfinpyrazone, metronidazole, allopurinol, cimetidine, amiodarone, disulfiram, ethanol
• hypoproteinemia
• liver failure
• intestinal malabsorptions
• inducers of hepatic catabolizing cytochromes : chronic administration of barbiturates, rifampicin, phenytoin / diphenylidantoin, ethanol, wide-leaf vegetables (red rape)
• carbamazepine
• corticosteroids
• glutethimide
• griseofulvin
• phenylbutazone
• primidone
• food rich in vitamin K, which helps produce some important blood clotting factors and may decrease the effects of anticoagulants if used at the same time
• antibacterial drugs which reduce vitamin K-producing symbiontic Bacteria
• cholestyramine binds to oral anticoagulants preventing their absorption
Side effects :
• hemorrhages (monitor PA and INR) :
• INR < 6 : Therapy : discontinue or reduce administration, administer platelet concentrates and fresh frozen plasma (FFP) (immediate action) first and vitamin K (long-term action) then => shift to LMWH
• INR = 6-10 : Therapy : 0.5 mg vitamin K i.v. or s.c.
• INR = 10-20 : Therapy : 3-5 mg vitamin K i.v. or s.c.
• INR > 20 : Therapy : 10 mg vitamin K i.v. or s.c.
• cutaneous necrosis (eschar) due to microvascular thromboses in patients with protein C deficiency : paradoxical effect due to inhibition of protein C synthesis, whose half-life is shorter than those of vitamin K-dependent pro-coagulant factors)
• alopecia
• urticaria
• dermatitis
• fever
• nausea
• diarrhea
• cramps
• anorexia
• teratogenic : contraindicated during pregnancy (replace with heparin) but can be used during lactation
• SNPs in CYP2C9 cause about 30% of patients to be slow warfarin metabolizers, which could result in high blood concentrations^ref. Moreover, polymorphisms in the vitamin K epoxide reductase multiprotein complex (VKORC) affect warfarin metabolism in rats^ref. Mutations in one of the complex's subunits, VKORC1, confer warfarin resistance in some human disorders. Overexpression of the wild-type protein made rats sensitive to the treatment. Testing for CYP2C9 polymorphisms does provide a better starting point for the warfarin dose in orthopedic patients^ref, which would achieve stable blood levels more quickly than trial-and-error dosing
• parenteral anticoagulants : thrombin inhibitors
• heparin (s.c. or i.v. ; IM causes hematoma, unabsorbed PO) produces its anticoagulant effects by binding to antithrombin III through a unique pentasaccharide molecule distributed randomly in the unfractionated heparin molecule (forming the unfractionated heparin antithrombin III complex) and inhibiting thrombogenesis primarily through inactivation of factors Xa (when the unfractionated hepatin is > 5 units per chain) and (when the unfractionated heparin is > 18 saccharide units) also to factor IIa. The longer saccharide units (> 18 units) comprise < 50% of the total fraction of LMWH (which has a mean of 15 saccharide units per chain) compared to 90% molecules in unfractionated heparin : thus, the ratio of antifactor Xa to antifactor II (Xa:IIa ratio) is > 1 for LMWHs
• unfractionated or high-molecular-weight heparins (HMWH) (3000 to 30,000 daltons) bind antithrombin III and inhibit thrombin only
• low-molecular-weight heparins (LMWH) (3000-7000 daltons) bind antithrombin III and inhibit factors IXa, Xa, XIa, XIIIa, and kallikrein. It has longer half-life (administered once per day) and doesn't affect aPTT values. LMWH has reduced binding to macrophages and endothelial cells, plasma proteins and PF4

	manufacturer	defractionation method	halflife (hrs)	factor Xa:IIa ratio (daltons)	average molecular weight (U)	indications
ardeparin / RD 11885 / WY-90493-RD (Normiflo®)	Wyeth-Ayerst	peroxidative depolymerization	1.2-3.3	1.8-2.0:1	5,600-6,500	prevention of DVT, PE after knee arthroplasty (50 U/kg q12h)
bioparin	Bioberica	?	?	?	?
certoparin (Alphaparin®, Mono-Embolex  NM®, Sandoparin®, Troparin®)	Sandoz => Novartis	amyl nitrate degradation	?	2:1	6000	moderate-risk surgical prophylaxis (3000 U 1-2 hrs pre, then 3000 U q.d.)
dalteparin / FR 860 / Kabi 2165  / tedelparin (Boxol®, Fragmin®, Low Liquemine®, Tedelparin®)	Pharmacia and Upjohn	nitrous acid depolymerization	2-4	2.0:1	4,000-6,400	prevention of DVT, PE after hip arthroplasty (5000 U q.d.), prevention of DVT, PE after abdominal surgery (2500 U q.d.), treatment of ACS (120 U/kg q12h (maximum recommended dosage is 10,000 U every 12 hours) + ASA 75-165 mg q.d.)
enoxaparin / PK-10169 / RP-54563 (Clexane®, Decipar®, Enoxaparine®, Lovenox®, Pharmuka 10169®, Plaucina®, Thrombenox®)	Rhone-Poulenc Rorer	benzylation and alkaline depolymerization	4.5	2.7:1	4,200	prevention of DVT, PE after knee arthroplasty (30 mg q12h), prevention of DVT, PE after hip arthroplasty (30 mg q12h or 40 mg q.d.), extended prevention of DVT after hip arthroplasty (40 mg q.d.), prevention of DVT, PE after abdominal surgery (40 mg q.d.), inpatient treatment of DVT with or without PE (1 mg/kg q12h or 1.5 mg/kg q.d.), outpatient treatment of DVT (1 mg/kg q12h), treatment of ACS (1 mg/kg q12h + ASA 100-325 mg q.d.)
miniparin	Syntex	?	?	?	?
nadroparin / CY 216D (Fraxiparin®, Fraxiparina®, Fraxiparine®, Seleparina®)	Sanofi-Winthrop	nitrous acid depolymerization	3.5	2-4:1	4,300-4500	moderate-risk surgical prophylaxis (3075 U 2-4 hrs pre and 12 hrs post, then 3075 U q.d.), high-risk surgical prophylaxis (41 U/kg 12 hrs pre and 12 hrs post, then 41 U/kg q.d. for 3 days, then 61 U/kg q.d.), treatment of VTE (92 U/kg q12h)
parnaparin sodium / OP 2123 (Alpha LMWH  Fluxum®, Minidalton®)	Opocrin => Aventis	cupric acid and hydrogen peroxide degradation OP-21-23	4	3:1	4,500-5,000	moderate-risk surgical prophylaxis (3200 U 2 hrs pre, then 3200 U q.d.), high-risk surgical prophylaxis (6400 U 12 hrs pre and 12 hrs post, then 6400 U q.d.)
reviparin sodium / LU 473111 (Clivarin®, Clivarine®)	Knoll	nitrous acid depolymerization	?	3-5:1	4,150-4,300	moderate-risk surgical prophylaxis (1750 U q.d.), high-risk surgical prophylaxis (4200 U 12h pre, then 4200 U q.d.), treatment of VTE (weight-based b.i.d. : dosage based on total body weight and administered twice/day: 35-45 kg, 3500 U; 46-60 kg, 4200 U; > 60 kg, 6300 U.)
tinzaparin / tinzaprin (Innohep®, Logiparin®, Novo LHN 1®)	Novo => DuPont Pharma	enzymatic degradation	1.3	1.9-2:1	4,900-6,500	inpatient treatment of DVT with or without PE (175 U/kg q.d.), moderate-risk surgical prophylaxis (3500 U 2 hrs pre, then 3500 U q.d.), high-risk surgical prophylaxis (50 U/kg 12 hrs pre, then 50 U/kg q.d. or 4500 U 12h pre, then 4500 U q.d.), treatment of VTE (175 U/kg q.d.)

Range of LMWH dosages in pregnancy :
• certoparin : 3000 U/day
• dalteparin : 2500-22,000 U/day
• enoxaparin : 2000-8000 (20-80 mg) U/day
• nadroparin : 2050-15,000 U/day
The antithrombin reactive center loop projects from the serpin body and adopts a canonical conformation that makes extensive backbone and side chain contacts from P5 to P6' with thrombin's restrictive specificity pockets, including residues in the 60-loop. These contacts rationalize many earlier mutagenesis studies on thrombin specificity. The 16-mer oligosaccharide is just long enough to form the predicted bridge between the high-affinity pentasaccharide-binding site on antithrombin and the highly basic exosite 2 on thrombin, validating the design strategy for this synthetic heparin^ref. The structure of the ternary complex between antithrombin, thrombin and a heparin mimetic (SR123781) reveals a template mechanism with antithrombin and thrombin bound to the same heparin chain. A notably close contact interface, comprised of extensive active site and exosite interactions, explains, in molecular detail, the basis of the antithrombotic properties of therapeutic heparin^ref.
1 U prevents 1 mL sheep blood (+ citrate) from coagulating for 1 hour after addition of 0.2 mL CaCl₂ 1%.
5,000 U => infusion with pump 700-2000 U / hr.
• Pitkin menstruum : a medium for the administration of heparin, consisting of a mixture of gelatin, dextrose, glacial acetic acid, and water.
aPTT has to be 1.5-2-fold normal value.
Used mainly when oral anticoagulants are counterindicated (e.g. during pregnancy).
Heparin is not absorbed by the oral route, requiring parenteral administration. It is principally metabolized in the liver by heparinase. Once absorbed into the blood, serum levels of LMWH remain steady and persist longer than unfractionated heparin. Like unfractionated heparin, LMWH is not well absorbed by muscle, fat, and lymphatic tissue. Despite its smaller size LMWH does not cross the placenta and can safely be used during pregnancy (FDA Pregnancy Category B, Dulitzki 1996)

property	LMWH	unfractionated heparin
plasma halflife t1/2	4 to 6 hours	1 to 2 hours
mechanism of action	antifactor Xa activity more than antifactor II activity	antifactor II activity more than antifactor Xa activity
elimination	renal, dose-independent	renal, dose-dependent
administration	subcutaneous	subcutaneous, intravenous, oral (trials)
monitoring anticoagulation	serum antifactor Xa necessary in patients with renal insufficiency and those with body weight < 50 kg or > 80 kg	aPTT
antidote	protamine sulfate not very effective.	protamine sulfate
dose	varies according to the indication  prophylaxis : 50-100 units of serum antifactor Xa/kg/d treatment : 200 units of serum antifactor Xa/kg/d	prophylaxis : 5000 units subcutaneously 2[times]/d or 3[times]/d therapy : 15 to 18 units/kg/hr adjusted to keep aPTT 1.5 to 2 times control

The longer half-life and better bioavailability of LMWH have been attributed to their decreased affinity and binding to endothelium, macrophages, and unfractionated heparin binding proteins^ref (Lane D, Lindahl U. Heparin binding and neutralizing proteins. Heparin: chemical and biochemical properties, clinical applications. Boca Raton: CRC Press 1989:363-391). The latter are acute phase reactants that increase in response to stress. Binding to heparin-binding proteins alters the bioavailability of unfractionated heparin to a greater degree than that of LMWH. The lower incidence of bleeding in patients treated with LMWH is thought to be from its reduced binding to platelets, endothelium, and Von Willebrand factor^ref. Because of their predictable antithrombotic response and longer bioavailability, LMWH can be used safely without daily anticoagulation monitoring in the majority of patients. Patients with renal insufficiency and those with body weight < 50 kg or > 80 kg have variable pharmacokinetics and so plasma antifactor Xa concentrations should be monitore.
Desirable properties of LMWH :
• superior bioavailability thanks to better absorption; less binding to plasma proteins; long plasma half-life; dose- independent clearance
• lower incidence of bleeding complications due to less binding to platelet surface proteins; less binding to endothelium; does not increase vascular permeability; low incidence of thrombocytopenia
• lower incident of heparin-induced thrombocytopenia due to less binding to platelet surface proteins; less binding to PF4; less binding to macrophages
• ease of administration and monitoring anticoagulation due to subcutaneous once or twice a day administration; predictable anticoagulation. Plasma antifactor Xa monitoring necessary in patients with renal insufficiency and those with body weights < 50 kg or > 80 kg.
• outpatient use : can be self administered subcutaneously by patient in an out patient setting with reasonable safety
FDA approved indications and dosage of LMWH
• prophylaxis in high risk abdominal surgery : enoxaparin 40 mg 1[times]/d or dalteparin 2,500-5,000 U 1[times]/d
• prophylaxis in total knee replacement : enoxaparin 30 mg 2[times]/d or ardeparin 50 units/kg Q12 hours
• prophyalaxis in total hip replacement : enoxaparin 20 mg 2[times]/d
• unstable angina and non-Q wave myocardial infarction (NQMI) : enoxaparin (Lovenox6) 1 mg/kg 2[times]/d plus aspirin
• deep venous thrombosis (DVT) treatment : enoxaparin 1 mg/kg 2[times]/d or 1.5 mg/kg 1[times]/d
Side effects :
• hemorrhages (monitor aPTT) : Therapy : protamine sulfate (1 mg every 80-115 heparin units)
• heparin-induced thrombocytopenia (HIT) : drop in PLT > 40% since onset of treatment

characteristic	type I HIT	type II HIT
frequency	10 to 20 %	1 to 3 %
timing of onset	2 to 3 days	5 to 10 days
nadir platelet count	100,000/µl	10,000 to 20,000/µl
antibody mediated	no (proaggregating effect of heparin itself)	Yes
thromboembolic sequelae	none	30 to 80 %
treatment	observe patient (reversible)	Discontinue heparin by all routes, select other anticoagulation, adjunctive therapy

Nomogram for monitoring anti-Xa levels in children receiving therapeutic doses of reviparin :

anti-Xa level (U/ml)	hold next dose	dosage change	repeat anti-Xa level
< 0.35	no	increase by 25%	4 hrs after next dose
0.35-0.49	no	increase by 10%	4 hrs after next dose
0.5-1.0	no	no	1 time/wk 4 hrs after a dose
1.1-1.5	no	decrease by 20%	4 hrs after next dose
1.6-2.0	no	decrease by 30%	4 hrs after next dose
> 2.0	yes, until anti-Xa level < 0.5	decrease by 40%	4 hrs after next dose

Heparin also acts as platelet antiaggregant and causes release of bFGF from dermatan sulfate.
Heparin limitations : indirect thrombin inhibitor (AT complex inhibits only soluble but not fibrin-bound thrombin : further heparin increases the affinity of thrombin for fibrin), non-specific binding to Ser proteases, endothelial cells, macrophages, reduced effect in ACS (inhibited by PF-4, clot-bound by thrombin), non-linear PK-PD, platelet activation)
• heparinoid is a mixture of anticoagulant GAGs with predominant antifactor Xa anticoagulant activity
• danaparoid sodium (Orgaran^®) is a mixture of nonheparin GAGs isolated from porcine intestinal mucosa (84% heparan sulfate, 12% dermatan sulfate, 4% chondroitin sulfate; M_r = 5500 kDa)
• lomoparan
• mesoglycan
• 4-amidinophenylbenzate hydrochloride (Pefabloc^®)
• 4-amidinophenylpiruvate
• phenylmethylsulfonyl fluoride (PMSF)
• recombinant nematode anticoagulant protein c2 (rNAPc2) (s.c.) : an 85-aminoacid protein that directly inhibits the fVIIa/tissue factor complex by a unique mechanism that requires initial binding of rNAPc2 to activated or zymogen factor X

• inhibitors of the initiation of coagulation work via inhibition of the factor VIIa/tissue factor complex
• defibrotide is a single-stranded polydeoxyribonucleotide with anti-thrombotic, anti-ischemic, anti-inflammatory and thrombolytic properties, but without systemic anticoagulant effects
• inhibitors of propagation of coagulation : parenteral and oral
• factor Xa inhibitors : the serine protease, factor Xa (FXa), is an attractive target for anticoagulants because of its pivotal "upstream" location in the coagulation cascade. FXa is situated at the start of the common pathway, where the intrinsic and extrinsic pathways converge, and at the primary site of amplification of the cascade. FXa is the rate-limiting component in the generation of thrombin. As a result, inhibition of one molecule of FXa prevents approximately 138 molecules of thrombin from being generated. Finally, the only function of FXa is to promote coagulation, without any of the other functions that are possessed by thrombin^{ref1, ref2}. For these reasons, the past decade has seen a virtual explosion of research into inhibitors of FXa as potential new antithrombotic agents^{ref1, ref2, ref3, ref4}
• indirect (antithrombin-dependent) FXa inhibitors : the action of indirect FXa inhibitors is mediated through their binding to and activation of antithrombin which then inhibits free FXa. Fondaparinux and idraparinux are synthetic analogs of the antithrombin-binding pentasaccharide sequence found in heparin and low molecular weight heparin (LMWH). These analogues are chemically modified to increase their affinity for antithrombin compared with heparin or LMWH. The chain length of these molecules is too short to bridge antithrombin to thrombin, a requirement for catalysis of inhibition of thrombin by antithrombin. Therefore, pentasaccharide-activated antithrombin is a specific inhibitor of FXa only. The properties of the indirect FXa inhibitors are very different from those of LMWH :

property	LMWH	fondaparinux	idraparinux
source	porcine mucosal heparin	chemical synthesis	chemical synthesis
molecular weight (daltons)	mean 5000	1728	1727
SC bioavailability	~ 90%	100%	100%
target(s)	multiple: FXa > FIIa >  FIXa, FXIa, FXIIa	FXa only	FXa only
binding to proteins other than target	yes	no	No
anti-Xa:anti-IIa	2–5:1	anti-Xa only	anti-Xa only
TFPI release from endothelium	yes	no	no
clearance	renal primarily	renal	renal
half life (SC route)	3–4 hrs	17–21 hrs	80–130 hours
effects of protamine	partial neutralization	no effect	no effect
potential for HIT	low	very low	very low

• fondaparinux sodium injection (Arixtra^©) [GlaxoSmithKline] is a novel synthetic heparin pentasaccharide capable of inhibiting factor Xa via the action of antithrombin (AT) but devoid of anti-factor IIa (thrombin) activity. Although the drug is identical in structure to the pentasaccharide domain found on unfractionated heparin (UH), it is too small to be recognized by the majority of heparin-reactive antibodies. It is theoretically an excellent candidate agent for the treatment of HIT. Currently, fondaparinux is licensed for orthopaedic venous thromboprophylaxis and acute coronary syndromes (OASIS-5/MICHELANGELO study) but not for the treatment of HIT^ref. It  Fondaparinux is a chemically modified (hypersulfated) pentasaccharide that binds avidly to antithrombin. This interaction induces a conformational change in antithrombin that increases its activity to selectively neutralize FXa (about 300-fold), thereby reducing thrombin generation^{ref1, ref2}. Once fondaparinux has activated antithrombin and the activated antithrombin binds to FXa, fondaparinux is released and is then available to bind to other antithrombin molecules in succession^ref. Fondaparinux has almost 100% bioavailability after subcutaneous injection, has rapid onset of action, does not bind to other plasma proteins, platelets, or endothelium, and is eliminated unchanged by the kidneys. The high affinity of fondaparinux for antithrombin results in a long half-life (approximately 18 hours), which enables once-daily dosing. Even at therapeutic doses, fondaparinux has minimal or no effect on the activated partial thromboplastin time (aPTT), international normalized ratio (INR), or bleeding time. Some of the potential advantages of fondaparinux over LMWH include its synthetic derivation, uniform composition, longer half-life, and absence of binding to plasma proteins (other than antithrombin). Fondaparinux does not bind to platelet factor-4 (PF4) or platelets and is, therefore, likely to be a safe and effective anticoagulant in patients with heparin-induced thrombocytopenia (HIT)^ref (Kuo KHM, Kovacs MJ. Successful treatment of heparin induced thrombocytopenia (HIT) with fondaparinux [abstract]. Blood. 2003;102:319a; Savi P, Chong B, Greinacher A, et al. Effect of fondaparinux on platelet activation in the presence of heparin-dependent anti-platelet antibodies. A blinded comparative multicenter study with unfractionated heparin [abstract]. Blood. 2003;102:319a; Warkentin TE, Cook RJ, Marder VJ, Kelton JG. Comparison of heparin-induced thrombocytopenia antibody (HIT-Ab) generation and in vitro cross-reactivity after elective hip or knee replacement surgery in patients receiving antithrombotic prophylaxis with fondaparinux or enoxaparin [abstract]. Blood. 2003;102:164a). Neither fondaparinux nor LMWH requires laboratory monitoring, while both agents are administered subcutaneously and both accumulate in the presence of renal insufficiency. The use of fondaparinux is contraindicated in patients with a creatinine clearance less than 30 mL/min and the drug should be used with caution in patients with moderate renal impairment (creatinine clearance 30–50 mL/min). Bleeding rates with fondaparinux were slightly increased in some prophylaxis trials, perhaps related to earlier initiation of dosing than LMWH comparators. Although approximately 1/3 of the patients in the four large orthopedic prophylaxis trials underwent neuraxial anesthesia and then received postoperative fondaparinux without a single epidural hematoma, the safety of fondaparinux in the setting of indwelling epidural catheters for postoperative analgesia has not been established. The anticoagulant and bleeding effects of fondaparinux are not reversed by protamine. However, high doses of recombinant FVIIa may be effective in this situation^ref. An extensive research program has evaluated fondaparinux as thromboprophylaxis in hospitalized patients, as therapy for VTE, and as an antithrombotic agent in cardiac disease.
• thromboprophylaxis after orthopedic surgery: > 7,000 patients undergoing elective hip or knee arthroplasty or hip fracture surgery were randomized in four large trials to receive 2.5 mg of fondaparinux or enoxaparin (EPHESUS, PENTATHLON 2000, PENTAMAKS, PENTHIFRA). Fondaparinux, started an average of 6 hours after the end of surgery, was significantly more efficacious than enoxaparin commenced 12–24 hours postoperatively^ref. Major bleeding (but not bleeding that was life-threatening or that required re-operation) was slightly more common in the patients who received fondaparinux. The difference in bleeding was seen only in the patients who started fondaparinux less than 6 hours after surgery; when fondaparinux was started 6 hours or more after surgery, bleeding was comparable to that seen with enoxaparin^ref. Therefore, the first dose of fondaparinux should be given at least 6 hours postoperatively. A recently completed trial (FLEXTRA) has compared the initiation of fondaparinux either 6 hours after hip and knee arthroplasty or the following morning. Results are pending.
• extended thromboprophylaxis after hip fracture: the PENTHIFRA-Plus trial randomized 656 hip fracture surgery patients to 1 week or 1 month of fondaparinux 2.5 mg daily^ref. Extended prophylaxis dramatically reduced the rates of both venographic DVT at 1 month (from 35% to 1%) and symptomatic VTE (from 3% to 0.3%). Although major bleeding was increased with extended prophylaxis (from 0.6% to 2.4%), clinically important bleeding was not increased.
• thromboprophylaxis after general surgery: the PEGASUS Trial compared prophylaxis with dalteparin 5000 U once daily (started preoperatively) to fondaparinux 2.5 mg once daily (started postoperatively) in almost 3000 high-risk patients undergoing abdominal surgery^ref. The 2 interventions had comparable efficacy and safety, except in the subgroup of patients with cancer, in which fondaparinux was more efficacious. APOLLO is an ongoing trial that is evaluating the addition of fondaparinux to sequential compression devices in general surgery patients.
• thromboprophylaxis in medical patients: the ARTEMIS Trial recently demonstrated that fondaparinux 2.5 mg SC significantly reduced the rate of asymptomatic DVT compared to placebo in 849 elderly medical patients, without causing major bleeding^ref. The secondary outcome, symptomatic VTE, was seen in 1.2% of placebo patients and in none of those who received fondaparinux (P = 0.03).
• acute treatment of DVT and PE: among patients who presented with acute VTE, the MATISSE-DVT and MATISSE-PE trials have shown that fondaparinux once daily was as at least as efficacious and safe as usual therapy with intravenous heparin or LMWH^{ref1, ref2}. In these studies, the fondaparinux dose was 7.5 mg for patients 50–100 kg, 5 mg for those < 50 kg, and 10 mg for those heavier than 100 kg.
• anticoagulation in acute coronary syndrome (UA, NSTEMI and STEMI) : fondaparinux appears to be at least as effective as IV heparin in acute myocardial infarction (PENTALYSE) or as LMWH in unstable angina (PENTUA)^{ref1, ref2}. Further Phase III studies are ongoing, including the Michelangelo OASIS-5 and OASIS-6 mega-trials in acute coronary syndrome and myocardial infarction, respectively.
• percutaneous coronary intervention: the ASPIRE Pilot Study has compared intravenous fondaparinux with heparin in patients undergoing urgent or elective percutaneous coronary interventions with concomitant aspirin plus clopidogrel. The extensive research program with fondaparinux demonstrates that it is a highly efficacious antithrombotic agent for prevention and treatment of both venous and arterial thromboembolic disorders. Fondaparinux is currently approved as thromboprophylaxis following hip and knee arthroplasty and hip fracture surgery, and as initial treatment for VTE. To date, fondaparinux has been studied in highly selected patients at relatively low bleeding risk. In these patients, bleeding was uncommon, although the risk appears to be increased by renal dysfunction (creatinine clearance < 30 mL/min), weight < 50 kg and initiation within 6 hours of a surgical procedure^ref. More data on the effectiveness and safety of fondaparinux in a more diverse spectrum of patients are necessary^ref
• idraparinux / SanOrg34006 [Sanofi-Synthelabo] - parenteral - is a chemically modified analog of fondaparinux that binds to antithrombin with such high affinity that the half-life of the drug approximates the half-life of antithrombin (80–130 hours)^ref. This allows once-weekly subcutaneous dosing. The Phase II PERSIST study compared 4 doses of idraparinux, given once a week, to warfarin in the treatment of acute DVT^ref. The lowest idraparinux dose, 2.5 mg, was as effective as higher doses and was associated with the least bleeding. Idraparinux is now being studied in large Phase III studies of VTE treatment (the Van Gogh DVT and PE trials), as well as in the long-term prevention of stroke among patients with atrial fibrillation (AMADEUS). Idraparinux may be useful in patients for whom therapeutic anticoagulation with vitamin K antagonists is problematic. However, the long half-life and lack of an antidote may be of concern especially if bleeding occurs or if a patient requires an invasive procedure. At least in healthy volunteers, the anticoagulant effect of idraparinux is reversed by recombinant FVIIa^ref
• direct (antithrombin-independent) FXa inhibitors : act by binding to and inhibiting FXa without the need for antithrombin. A number of synthetic direct FXa inhibitors are undergoing clinical evaluation. These agents inhibit both free FXa and FXa bound to activated platelets that are trapped within a thrombus as part of the prothrombinase complex. This property may confer a therapeutic advantage to the direct FXa inhibitors compared with heparin, LMWH, and the indirect FXa inhibitors. These drugs appear to inhibit thrombus formation while allowing sufficient thrombin to be generated to activate platelets (and therefore to maintain the ability to form a hemostatic plug). As a result, these agents may also have a lower bleeding potential than conventional anticoagulants and direct thrombin inhibitors^ref
• BAY 59-7939 [Bayer] – oral - is currently being assessed in Phase II trials of the treatment of acute DVT (ODIXa-DVT) and prevention of DVT after knee arthroplasty.
• DPC-423 [Bristol-Myers Squibb] – oral
• DX-9065a [Daiichi] – parenteral/oral. Intravenous administration is being assessed in patients with acute coronary syndrome and those undergoing percutaneous coronary interventions, while the oral preparation of this anticoagulant is being evaluated after major knee surgery^ref
• LY517717 [Lilly] – oral is undergoing Phase II evaluation as thromboprophylaxis following elective hip and knee arthroplasty
• razaxaban (DPC906) [Bristol-Myers Squibb] is an oral direct FXa inhibitor that has recently been tested in a Phase II trial of thromboprophylaxis following knee arthroplasty^ref
• rivaroxaban (Xarelto^®; source : Bayer)  is an investigational, oral, once-daily DFI
• otamixaban / XRP0673
• sulodexide / KRX-101 (Vessel Due F^©)
• (recombinant) tick anticoagulant peptide (TAP)
Monitoring of anticoagulant activity of FXa inhibitors : because of their predictable pharmacokinetics, monitoring of the various FXa inhibitors appears to be unnecessary for most patients. Furthermore, the assay techniques and target ranges for the anti-Xa activity of these agents have not been rigorously standardized. In fact, there is very little information relating anti-Xa levels to clinical outcomes (thrombosis prevention or bleeding) for any anticoagulant. If laboratory monitoring of fondaparinux is performed, the anti-Xa assay must be calibrated with fondaparinux^ref. The development and evaluation of FXa inhibitors may identify new parenteral and oral antithrombotic agents that demonstrate improvements in effectiveness, safety, convenience and cost-effectiveness compared with current anticoagulants. It is not yet clear whether fondaparinux has a clinically important advantage over LMWH, although it may be safer from the perspective of HIT risk. As a once-weekly injection, idraparinux may be more convenient than LMWH in treatment and prophylaxis, and it may replace oral vitamin K antagonists in selected patients. The parenteral direct FXa inhibitors may compete with bivalirudin in coronary interventions. Finally, the oral direct FXa inhibitors might be used in situations where oral vitamin K antagonists are currently used. They will also need to be compared to oral direct thrombin inhibitors. The ultimate role of each of these new agents requires further clinical trials.
• factor IXa inhibitors
• inhibitors of factor Va and VIIIa
• activated protein C
• soluble thrombomodulin
• SNAC-heparin
• direct factor II (thrombin) inhibitors (DTI) are under development both for parenteral and oral administration

Thrombin is a trypsin-like serine protease. Among its many biologic roles, alpha-thrombin functions as a procoagulant by hydrolyzing ("activating") its substrates, including factor (F) I (fibrinogen), FV, FVIII, FXI, FXIII, and the platelet protease activated receptors (PAR), PAR-1 and PAR-4. Thrombin’s exquisite substrate specificity derives from surface binding sites (e.g., exosite 1) that are specific for its substrates. Glycosaminoglycans, such as unfractionated heparin and low-molecular-weight heparin, indirectly inhibit thrombin by catalyzing the serine protease inhibitor, antithrombin, which covalently binds to the active site of thrombin. In contrast, direct thrombin inhibitors (DTIs) inhibit thrombin by directly binding to exosite 1 and/or the active site of thrombin. DTIs have potential advantages over heparin. Unlike heparin, they produce a predictable anticoagulant response because they exhibit minimal binding to plasma protein. DTIs also do not bind platelet factor 4 and, thus, do not crossreact with autoantibodies that cause heparin-induced thrombocytopenia (HIT). DTIs inhibit fibrin-bound thrombin as well as fluid-phase thrombin. DTIs do not act through inhibition of vitamin K. Thus, DTIs do not suffer the same problems with food interactions as do oral vitamin K inhibitors (e.g., warfarin), and the potential for drug-drug interactions appears to be low. Finally, the therapeutic window of some DTIs (e.g., melagatran/ximelagatran) is sufficiently broad that routine laboratory monitoring and dose adjustment is unnecessary. DTIs also have potential disadvantages. Currently, there is no antidote for rapid reversal of their anticoagulant effect. In animal models, activated prothrombin complex concentrates (e.g., Feiba^®, Autoplex^®) appear to be effective in reducing the bleeding time and blood loss associated with high plasma DTI concentrations, as does activated factor VII (FVIIa, Novoseven^®). In addition, available DTIs exhibit substantive differences in their pharmacology that may translate into important differences in efficacy, safety and convenience, and they are considerably more expensive than heparin or warfarin.
• bivalent (binding active site and exosite 1) :
• recombinant hirudin derivatives : originally isolated from the medicinal leech, hirudin is a 65-amino-acid polypeptide that binds thrombin at both the active site and exosite 1. Hirudin forms a 1:1 stoichiometric complex with thrombin of such high affinity that thrombin inhibition is essentially irreversible. Recombinant hirudins (M_r = 698 Da; K_i = 0.2 x 10^–12 mol/l) have a leucine for isoleucine substitution at the N-terminal end of the molecule :
• desirudin (Revasc^®; cloned in Saccharomyces cerevisiae; source : Novartis Pharma, Switzerland) differs from lepirudin by having a valine-1, valine-2 substitution for the wild-type leucine-1, threonine-2. Both desirudin and lepirudin lack a sulfate group on tyrosine-63.
• lepirudin / Leu¹-Thr²-63-desulfohirudin (Refludan^®; cloned in Saccharomyces cerevisiae; source : Roussel Uclaf, France => Berlex Labs, Germany) reduces new TECs by 63%, deaths by 49% and limb amputation by 38%. Most common adverse evens are bleeding, such as from puncture sites and wounds (14%), anemia (13%), and hematoma (11%). It is approved in the US for anticoagulation in patients with HIT and associated thrombosis (HITT).
Hirudin must be administered parenterally. The plasma half-life (t) ranges from 1 hour when administered intravenously to 2 hours when administered subcutaneously, and the drug is eliminated via the kidneys. Hirudin has a narrow therapeutic window. Consequently, the anticoagulant effect must be monitored and the dose adjusted to maintain the activated partial thromboplastin time (aPTT) within a therapeutic range (aPTT ratio of 1.5–2.0 4 hours after initiation or a dose change). The correlation between plasma hirudin levels and the aPTT is not linear. Consequently, at higher hirudin doses, monitoring with the ecarin clotting time (ECT) is preferable. Dose adjustment is required for patients with impaired renal function. Rarely, patients treated with hirudin may develop non-neutralizing anti-hirudin antibodies that prolong the hirudin anticoagulant effect because of delayed hirudin-antibody complex clearance.
• bivalirudin (hirulog) (Angiomax^®) (M_r = 218 Da; K_i = 2.3 x 10^–9 mol/l; t_1/2 = 25 min; excretion : non renal, non hepatic) inhibits both fibrin-bound and circulating thrombin, completely blocking thrombin-mediated platelet aggregation. It is a synthetic 20-amino-acid polypeptide hirudin analog, consists of an NH₂-terminal D-Phe-Pro-Arg-Pro domain that interacts with the thrombin active site, a linker region of 4 glycine residues, and a dodecapeptide analog of the hirudin carboxy-terminus that binds exosite 1 on thrombin. Once bound, thrombin cleaves the Pro-Arg bond within the NH₂-terminus of bivalirudin. Thus, unlike hirudin, bivalirudin is a reversible inhibitor. Bivalirudin is currently marketed in the US as an alternative to heparin in patients undergoing percutaneous coronary interventions (PCI). Bivalirudin also must be administered parenterally and has a plasma half-life of 25 minutes after intravenous injection. Elimination is via degradation by endogenous peptidases. Bivalirudin typically is administered as a weight-adjusted (1 mg/kg) bolus dose given immediately prior to PCI, followed by a 4-hour infusion (0.2 mg/kg/h). Compared with hirudin, bivalirudin appears to cause less bleeding, possibly due to the reversible thrombin inhibition and shorter plasma half-life. The activated clotting time (ACT) is a point-of-care test that was developed for rapid, bedside monitoring of heparin therapy in patients undergoing cardiac catheterization or cardiopulmonary bypass surgery^ref : additional bolus dosing is given if the ACT is < 350 seconds. The ecarin clotting time is a measurement involving the use of ecarin, an enzyme found in snake venom (Echis carinatus), which converts prothrombin to meizothrombin. Meizothrombin, an intermediary thrombin derivative^ref, is particularly sensitive to inactivation by direct thrombin inhibitors. The ecarin clotting time is more closely correlated with bivalirudin levels (r=0.9) than is the activated clotting time (r=0.7)^ref. There is no linear correlation between the standard activated clotting time and the plasma bivalirudin concentration^{ref1, ref2}. Several studies have shown that the standard activated clotting time does not provide an accurate measurement of the anticoagulation effect of bivalirudin, especially at large doses^{ref1, ref2, ref3}. However, there is a good linear relationship between the bivalirudin concentration and the ecarin clotting time^ref. Commercial ecarin-clotting-time assays, however, are generally limited to reference laboratories and are not available in the form of point-of-care testing required for cardiac catheterization, cardiac surgery, or both
• univalent (active site, noncovalent) :
• argatroban (Argatroban^©) - IV- (M_r = 527 Da; K_i = 3.9 x 10^–8 mol/l; t_1/2 = 45 min; excretion : biliary secretion), a synthetic peptidomimetic L-arginine derivative that acts as a competitive DTI, is the first clinical anticoagulant solely to target thrombin. For some time, this drug has been used in Japan for the management of thromboembolic disorders. Recently, it has been approved in Japan for use in thrombotic and ischaemic stroke. Despite a large number of preclinical studies on the pharmacology of this agent, clinical trials in Europe and North America were only initiated in 1996. Argatroban produces anticoagulant effects comparable to therapeutic heparinisation at concentrations of approximately 1 mg/ml. At concentrations of 5-10 mg/ml, this agent produces adequate anticoagulation for interventional cardiovascular procedures and prolongs the activated clotting time (ACT) to 400-600 s. The predictable anticoagulant effect of this agent is relatively short lasting, and may not warrant pharmacologic neutralisation in the majority of patients. However, patients with hepatic dysfunction may need some means of neutralisation. Unlike heparin, this drug produces its anticoagulant effects by direct inhibition of thrombin and thrombin-mediated processes. This agent is not influenced by endogenous factors such as platelet factor 4 and other proteins which bind heparin. Argatroban's use does not lead to the formation of antiplatelet antibodies. Thus, this drug is useful in the management of heparin induced thrombocytopenic (HIT) patients. Although argatroban was initially developed for the management of deep vein thrombosis (DVT), based on its pharmacologic properties, it can be developed for safer anticoagulation in such indications as acute coronary syndromes, as an adjunct to thrombolytics, thrombotic and ischaemic stroke and inflammatory diseases resulting in thrombotic complications^ref. Argatroban is currently marketed in the US for prophylaxis or therapy of patients with HIT and for anticoagulation in HIT patients undergoing PCI. The anticoagulant activity of argatroban is monitored using the aPTT and the dose is adjusted to achieve an aPTT ratio of 1.5–3.0. Argatroban is metabolized in the liver and must be used with caution among patients with hepatic dysfunction; it is the drug of choice for patients with severe renal impairment. Argatroban prolongs the INR more than other DTIs, a feature that can complicate overlap therapy with vitamin K antagonists.
• ximelagatran (Exanta^©; Exarta™ in Italy and Sweden) (M_r = 474 Da; K_i = 37 x 10^–8 mol/l; t_1/2 = 3-5 hrs) - oral -, an uncharged, lipophilic prodrug, exhibits 20% bioavailability after oral administration. Ximelagatran produces a predictable anticoagulant response, and no food or drug interactions have been documented. Consequently, routine anticoagulation monitoring is unnecessary. About 6% of patients treated with ximelagatran develop an increase in alanine aminotransferase (ALT) that is usually asymptomatic, unaccompanied by a concomitant increase in bilirubin, and reversible whether or not ximelagatran is continued. Once absorbed,  => melagatran (M_r = 430 Da; K_i = 0.2 x 10^–8 mol/l; t_1/2 = 2-3 hrs), a dipeptide mimetic of the region of fibrinopeptide A that interacts with thrombin’s active site. Melagatran has poor oral bioavailability and must be given subcutaneously. About 80% of melagatran is excreted via the kidneys => inogatran; for treatment of deep vein thrombosis (DVT)^ref, stroke prevention in patients with nonvalvular atrial fibrillation^ref, stroke prophylaxis in chronic atrial fibrillation^ref. On February 14, 2006, AstraZeneca announced that the company has decided to withdraw it from the market and terminate its development because of reports of severe hepatitis in the EXTEND clinical trial. AstraZeneca estimates that approximately 400 patients are currently being prescribed the drug for short-term prevention of venous thromboembolism (VTE) following orthopaedic surgery (OS). 2 ongoing Exanta clinical trials will be discontinued and Exanta-treated patients switched to other treatments
• dabigatran etexilate / BIBR-1048 (K_i = 4.5 x 10^–8 mol/l; t_1/2 = 12 hrs; renal excretion) is an oral prodrug that is converted to dabigatran, a potent benzamidine-based thrombin inhibitor. Dabigatran is currently undergoing Phase III evaluation for thromboprophylaxis after total knee replacement surgery (TKR) and Phase II evaluation for treatment of VTE and for stroke prevention in atrial fibrillation.
Clinical trials :
• VTE prophylaxis (primary prevention) : desirudin, bivalirudin, melagatran/ximelagatran, and ximelagatran alone have been evaluated as VTE prophylaxis after elective total hip replacement (THR) or TKR. All studies used symptomatic VTE and DVT detected by routine venography as the endpoint. In addition, recombinant hirudin, bivalirudin, melagatran, ximelagatran, and LMWH were administered as fixed doses without laboratory monitoring. In a Phase III trial, 1587 THR patients were randomized to desirudin or enoxaparin sodium (40 mg SC QD)^ref. The overall VTE and proximal DVT rates after surgery were significantly lower with desirudin than with enoxaparin. There was no significant difference in bleeding between the two groups. Bivalirudin was evaluated in a small Phase II trial involving 177 patients undergoing THR or TKR^ref. The highest bivalirudin dose regimen tested (1.0 mg/kg SC Q 8 hours) was associated with a 17% overall (2% proximal) postoperative DVT rate. Bleeding rates were low with all doses tested.
• ximelagatran has been compared with either LMWH or warfarin prophylaxis in a series of trials. In an initial Phase II study, 600 TKR patients were randomly assigned to ximelagatran in blinded twice-daily doses of 8, 12, 18, or 24 mg, or open-label enoxaparin (30 mg SC twice daily)^ref. Treatments were started 12–24 hours after surgery and continued for 6–12 days. The postoperative rates of overall VTE and proximal DVT or pulmonary embolism (PE) with ximelagatran 24 mg and enoxaparin did not differ significantly. In a subsequent Phase III trial, 1838 patients undergoing elective THR were randomly assigned to prophylaxis with oral ximelagatran (24 mg BID) or enoxaparin (30 mg SC BID) started the morning after surgery^ref. Both the overall VTE and proximal DVT or PE rates were higher with ximelagatran. Rates of major bleeding were low. Ximelagatran versus low-molecular-weight heparin (LMWH) or warfarin in the prevention of venous thromboembolism (VTE) :

surgery	Variable	ximelagatran BID				LMWH or warfarin
total knee replacement (TKR)ref(N = 600)	dose	8 mg	12 mg	18 mg	24 mg	enoxaparin 30 mg BID
	overall VTE	27.0%	19.8%	28.7%	15.8%	22.7%
	proximal DVT	6.6%	2.0%	5.8%	3.2%	3.1%
	major bleeding	0	0	2.4%	0	0.8%
TKRref(N = 1838)	dose	24 mg				enoxaparin 30 mg BID
	overall VTE	7.9%				4.6%
	proximal DVT	3.6%				1.2%
	major bleeding	0.8%				0.9%
TKRref(N = 680)	dose	24 mg				warfarin INR 2.5, range 1.8–3.0
	overall VTE	19.2%				25.7%
	proximal DVT	3.3%				5.2%
	major bleeding	1.7%				0.9%
TKRref EXULT (N = 2301)	dose	24 mg		36 mg		warfarin INR 2.5, range 1.8–3.0
	overall VTE	24.9%		20.3%		27.6%
	proximal DVT	2.5%		2.7%		4.1%
	major bleeding	4.8%		5.3%		4.5%

2 clinical trials compared ximelagatran with adjusted-dose warfarin. In a Phase III trial, 680 patients undergoing TKR were randomly assigned to ximelagatran (24 mg BID, started on the morning after surgery) or warfarin (INR 2.5, range 1.8–3.0, started on the evening after surgery)^ref. Overall VTE and proximal DVT rates were not significantly different between the ximelagatran and warfarin groups (19.2% vs 25.7%, respectively, P = 0.07, and 3.3% vs 5.0%, respectively, P > 0.2). Rates of major and minor bleeding were low and not significantly different. In the second trial (EXULT phase 1), 2301 patients undergoing TKR were randomly assigned to ximelagatran (24 mg or 36 mg BID, started the morning after surgery) or warfarin (target INR 2.5; range 1.8–3.0; started the evening of surgery)^ref. The rates of overall VTE and death were significantly lower in the ximelagatran 36 mg group than in the warfarin group (P = 0.003). Rates for proximal DVT and major and minor bleeding were not significantly different. Based on these data, the second phase of the EXULT trial randomized an additional 2300 patients to ximelagatran (36 mg BID) or warfarin. The results are not yet available. 3 large studies compared the combination of melagatran and ximelagatran with LMWH as prophylaxis for THR or TKR patients. In a Phase II study (METHRO II), 1900 patients were randomly assigned to one of four melagatran/ximelagatran doses (1.0/8 mg, 1.5/12 mg, 2.25/18 mg, or 3.0/24 mg)^ref. The first melagatran dose was injected subcutaneously immediately before surgery but after administration of neuraxial (spinal or epidural) anesthesia. A second melagatran injection was given 7–11 hours after surgery, followed by twice daily injections until oral ximelagatran could be started (usually 1–3 days after surgery). A highly significant dose-dependent decrease in VTE (both overall and proximal DVT) was seen with increasing doses of melagatran/ximelagatran. Melagatran/ximelagatran versus low molecular weight heparin (LWMH) in the prevention of venous thromboembolism (VTE) :
 

surgery	variable	melagatran SC/ximelagatran PO BID				LMWH
total hip replacement (THR) or total knee replacement (TKR)ref (N = 1900) MEHTRO II	dose	melagatran/ximelagatran				dalteparin 5000 IU QD
		1 mg/8 mg	1.5 mg/12 mg	2.25 mg/18 mg	3 mg/24 mg
	overall VTE proximal DVT major bleeding	37.8 8.5 0.8	24.1 6.2 1.2	23.7 3.3 3.5	15.1 2.1 5.5	28.2% 5.5 2.3
THR or TKRref (N = 2788) METHRO III	dose overall VTE proximal DVT major bleeding	3 mg melagatran/Ximelagatran 24 mg 31.0% 5.7% 1.4%				enoxaparin 40 mg QD 27.3% 6.2% 1.7%
THR or TKRref (N = 2764) EXPRESS	dose overall VTE proximal DVT major bleeding	2/3 mg melagatran/Ximelagatran 24 mg 20.3% 2.3% 3.3%				enoxaparin 40 mg QD 26.7% 6.3% 1.2%

In a subsequent Phase III study (METHRO III), 2788 patients undergoing elective THR or TKR were randomized to melagatran/ximelagatran or enoxaparin^ref. Melagatran (3 mg SC) was given 4–12 hours after surgery followed by oral ximelagatran (24 mg BID). Enoxaparin (40 mg SC) was started on the evening before surgery and continued daily thereafter. The overall VTE rate was lower with enoxaparin (absolute difference 3.7% [P = 0.053] in favor of enoxaparin). This difference was entirely accounted for by an increased rate of calf vein thrombosis in the melagatran/ximelagatran group. The major VTE rates of proximal DVT or PE did not differ significantly (melagatran/ximelagatran, 5.7%, vs enoxaparin, 6.2%), nor did severe bleeding, transfusion requirements, or blood loss. In a final Phase III study (EXPRESS), 2764 patients undergoing THR or TKR were randomly assigned to melagatran started before surgery and postoperative oral ximelagatran, or enoxaparin in the same dose schedule as the METHRO III study^ref. Melagatran (2 mg SC) was given immediately before surgery and again (3 mg SC) on the evening of surgery, followed by oral ximelagatran (24 mg BID). The overall VTE and proximal DVT rates were significantly lower in the melagatran/ximelagatran group than in the enoxaparin group. While bleeding events (3.3% and 1.2%) and transfusion rates (66.8% and 61.7%) were more common in the melagatran/ximelagatran group, there were no significant differences between the two groups in fatal bleeding, critical organ bleeding, or bleeding requiring reoperation. In summary, postoperative ximelagatran (36 mg BID) is at least as effective as warfarin for thromboprophylaxis after TKR. Because routine lab monitoring is unnecessary, ximelagatran may be particularly useful for extended out-of-hospital prophylaxis in high-risk orthopedic patients. The combination of subcutaneous melagatran started prior to surgery followed by oral ximelagatran postoperatively is more effective than enoxaparin for thromboprophylaxis after THR or TKR, but may cause more bleeding.
• acute venous thromboembolism therapy (secondary prevention) : only one study has tested recombinant hirudin as treatment for acute VTE. In a Phase II trial, 155 DVT patients were randomly allocated to 1 of 3 subcutaneous hirudin doses (0.75, 1.25, or 2.0 mg/kg SC BID) or to adjusted-dose intravenous unfractionated heparin^ref. All patients received baseline and post-treatment venograms and ventilation/perfusion lung scans. After 5 days of treatment, the rates of DVT progression or regression, new ventilation/perfusion mismatches, and adverse events did not differ between the four groups. A series of clinical trials tested ximelagatran as treatment for acute VTE. Similar to the prophylaxis trials, ximelagatran was administered as a fixed oral dose and without laboratory monitoring or dose adjustment. In the THRIVE treatment trial, 2489 patients with acute DVT (~35% with associated PE) were randomly assigned to either ximelagatran 36 mg BID or enoxaparin 1 mg/kg SC BID (5–20 days) followed by warfarin (INR 2.0–3.0) (Huisman MV, on behalf of the THRIVE II & V investigators. Efficacy and safety of the oral direct thrombin inhibitor ximelagatran compared with current standard therapy for acute symptomatic deep vein thrombosis, with or without pulmonary embolism: a randomized, double-blind, multinational study [abstract]. J Thromb Haemost 2003, supplement 1, #OC003). After 6 months of therapy, the cumulative incidence of recurrent VTE was 2.0% in the enoxaparin/warfarin group and 2.1% in the ximelagatran group. Major bleeding and all-cause mortality were 2.2% and 3.4%, respectively, in the enoxaparin/warfarin group, and 1.3% and 2.3% in the ximelagatran group. The incidence of increased ALT (> 3-fold above the upper normal limit) was 2% in the enoxaparin/warfarin group and 9.6% in the ximelagatran group. In the THRIVE III trial, 1233 VTE patients who had completed 6 months of conventional anticoagulation therapy were randomized to ximelagatran (24 mg BID) or placebo for an additional 18 months^ref. Among the 612 patients receiving ximelagatran, 12 developed recurrent VTE. In contrast, 71 of the 611 patients receiving placebo developed recurrent VTE (hazard ratio 0.16; 95% CI: 0.09–0.30; P < 0.001). All-cause mortality, and major and minor bleeding rates did not differ significantly between the two groups. Again, patients given ximelagatran were more likely to develop increased serum ALT than those randomized to placebo (6.4% and 1.2%, respectively). In summary, oral ximelagatran is as effective as conventional anticoagulation with LMWH followed by warfarin for initial treatment of patients with VTE. Rates of major bleeding are similar with ximelagatran and conventional therapy.
• acute coronary syndromes : recombinant hirudin is as effective as unfractionated heparin for adjunctive therapy among patients with unstable angina or acute myocardial infarction (MI) undergoing thrombolysis^ref. However, because of its narrow therapeutic window and high bleeding risk, hirudin has not replaced heparin for this indication. In the Phase II ESTEEM trial, 1883 patients with documented ST-elevation or non-ST-elevation MI within the past 14 days were randomized to ximelagatran (24, 36, 38 or 60 mg BID) or placebo for 6 months as secondary prevention^ref. All patients received aspirin (160 mg daily) and optimal medical management, including statins and ACE inhibitors. All four ximelagatran doses significantly reduced the frequency of the primary endpoint, a composite of all-cause mortality, MI and severe recurrent ischemia, by about 4% compared with placebo. There was no evidence of a dose-response. When placebo was compared with the 4 combined ximelagatran dose groups, ximelagatran produced a statistically significant 24% reduction in the composite endpoint from 16.3% to 12.7% (hazard ratio 0.76; 95% CI of 0.59–0.98; P = 0.036). Major bleeding and mortality rates were low and similar between the groups. However, minor bleeding occurred in 13% and 22% of those given placebo and ximelagatran, respectively. Based on this information, a Phase III trial using the 24 mg twice-daily dose of ximelagatran is under consideration.
• percutaneous coronary intervention : bivalirudin is approved as an alternative to heparin in patients undergoing PCI^ref; recent meta-analyses suggest that bivalirudin is more effective than heparin for this indication^ref. Compared with unfractionated heparin, bivalirudin also appears to cause less bleeding and to reduce the need for adjunctive treatment with glycoprotein (GP) IIb/IIIa antagonists in patients undergoing coronary stenting^ref. The incidence of death, MI, or repeat revascularization by 6 months, and death by 1 year, also were no different among PCI patients receiving bivalirudin and provisional GPIIb/IIIa blockade versus unfractionated heparin and planned GPIIb/IIIa blockade^ref
• stroke prevention in atrial fibrillation : 2 Phase III trials evaluated ximelagatran as stroke prevention among patients with non-valvular atrial fibrillation and at least one additional stroke risk factor. The SPORTIF III trial (N = 3410) was an open-label study conducted in Europe, whereas the SPORTIF V trial (N = 3922) was a double-blind study done in North America. Both trials randomized patients to either warfarin (INR 2.0–3.0) or ximelagatran 36 mg BID. In the SPORTIF III trial, the stroke or systemic arterial embolism rates were 2.3% and 1.6% per year for warfarin and ximelagatran, respectively (P = 0.10), over 4941 person-years of treatment^ref.18 While rates for disabling or fatal stroke, mortality, and major bleeding were similar, combined major and minor bleeding rates were significantly lower in the ximelagatran group (25.8% vs. 29.8% per year). In the SPORTIF V trial, the stroke or systemic arterial embolism rates were 1.6% and 1.2% for ximelagatran and warfarin, respectively (P = 0.13). Rates of major bleeding were 2.4% and 3.1% in those given ximelagatran and warfarin, respectively (P = 0.16), whereas total bleeding (major and minor bleeding) were 37% and 47%, respectively (P < 0.001). When the results of SPORTIF III and SPORTIF V are combined, ximelagatran was associated with a .03% absolute risk reduction in the rate of stroke and systemic embolism relative to warfarin (P = 0.94) and a 0.6% reduction in the rate of major hemorrhage (P = 0.05). Using the composite outcome of stroke, systemic embolism, major hemorrhage and death, ximelagatran produced a relative risk reduction of 16%, reducing the rate from 6.2% to 5.2% (P = 0.038). In summary, ximelagatran is at least as effective as warfarin in preventing stroke and systemic embolic events without an increased risk of major bleeding.
• prophylactic fibrinolysis through selective dissolution of nascent clots by tissue plasminogen activator (tPA)-carrying erythrocytes can dissolve nascent clots from within the clot, in a Trojan horse–like strategy, while having minimal effects on preexisting hemostatic clots or extravascular tissue,  thereby reducing the risk of bleeding. After intravenous injection, the fibrinolytic activity of RBC-tPA persisted in the bloodstream at least 10-fold longer than did that of free tPA. In a model of venous thrombosis induced by intravenously injected fibrin microemboli aggregating in pulmonary vasculature, soluble tPA lysed pulmonary clots lodged before but not after tPA injection, whereas the converse was true for RBC-tPA. Free tPA failed to lyse occlusive carotid thrombosis whether injected before or after vascular trauma, whereas RBC-tPA circulating before, but not injected after, thrombus formation restored blood flow. This RBC-based drug delivery strategy alters the fibrinolytic profile of tPA, permitting prophylactic fibrinolysis.
• platelet activation at sites of vascular injury is essential for the arrest of bleeding; however, excessive platelet accumulation at regions of atherosclerotic plaque rupture can result in the development of arterial thrombi, precipitating diseases such as acute myocardial infarction and ischemic stroke. Rheological disturbances (high shear stress) have an important role in promoting arterial thrombosis by enhancing the adhesive and signaling function of platelet integrin a_IIbb₃ (GPIIb-IIIa). Type Ia phosphoinositide 3-kinase (PI3K) p110 isoform has a key role in regulating the formation and stability of integrin a_IIbb₃ adhesion bonds, necessary for shear activation of platelets. Isoform-selective PI3K p110 inhibitors have been developed which prevent formation of stable integrin a_IIbb₃ adhesion contacts, leading to defective platelet thrombus formation. In vivo, these inhibitors eliminate occlusive thrombus formation but do not prolong bleeding time. These studies define PI3K p110 as an important new target for antithrombotic therapy^ref.

	dosage	duration	thromboselectivity	disadvantages
Serratia peptidase / serrapeptase (Danzen©)			selective
alteplase / r-tPA (Activase®, Actilyse® (cloned in CHO cells; source : Genentech Inc, USA)) began to be commonly used to restore the patency of occluded central venous catheters (CVCs) as urokinase production was halted in the late 1990s	100 mg	4 hours	selective	high cost
amediplase is a chimeric protein which combines part of the tissue plasminogen activator (tPA) and part of the single-chain urokinase plasminogen activator (sc-UPA). Administration in a bolus injection, which constitutes an advantage over the standard thrombolytic treatments. Currently it is in Phase III clinical trial.	80 mg in 1 hour	7 hours	selective	high cost
reteplase / deletion mutant r-tPA (Rapilysin® (cloned in Escherichia coli; source : Boehringer Mannheim, T/A Roche Diagnostics, Germany), Retavase©) has been reported to restore patency to CVCs in 30 minutes; it is used for the treatment of ischaemic stroke within 3 hours of symptom onset			selective
tenecteplase / 3 mutations r-tPA (Metalyse® (cloned in CHO cells; source : Genentech Inc, USA), TNKase®)			selective
desmoteplase / recombinant Desmodus rotundus salivary plasminogen activator (DSPA alpha-1) (source : PAION GmbH, under license from Schering AG) is currently undergoing phase II clinical trial for treatment of acute ischaemic stroke. DSPA, unlike tPA, does not promote kainate- or NMDA-mediated neurotoxicity in vivo. The distinguishing characteristic of vampire bat salivary plasminogen activators (DSPAs) is their strict requirement for fibrin as a cofactor. DSPAs consist of structural modules known from u-PA and t-PA such as finger (F), epidermal growth factor (E), kringle (K), and protease (P), combining to 4 genetically and biochemically distinct isoenzymes, exhibiting the formulas FEKP (DSPA alpha 1 and alpha 2) and EKP and KP (DSPA beta and DSPA gamma). Only DSPA alpha 1 and alpha 2 bind to fibrin. All DSPAs are single-chain molecules, displaying substantial amidolytic activity. In a plasminogen activation assay, all 4 DSPAs are almost inactive in the absence of fibrin but strongly stimulated by fibrin addition. The catalytic efficiency (kcat/Km) of DSPA alpha 1 increases 105-fold, whereas the corresponding value of t-PA is only 550. The ratio of the bimolecular rate constants of plasminogen activation in the presence of fibrin versus fibrinogen (fibrin selectivity) of DSPA alpha 1, alpha 2, beta, gamma, and t-PA was found to be 13,000, 6500, 250, 90, and 72, respectively. Whereas all DSPAs are therefore more fibrin dependent and fibrin selective than t-PA, the extent depends on the respective presence of the various domains. The introduction of a plasmin-sensitive cleavage site in a position akin to the one in t-PA partially obliterates fibrin cofactor requirement. Fibrin dependence and fibrin selectivity of DSPAs are accordingly mediated by fibrin binding, which involves the F domain, as yet undefined determinants within the K and P domains, and by the absence of a plasmin-sensitive activation site. These findings transcend the current understanding of fibrin-mediated stimulation of plasminogen activation: in addition to fibrin binding, specific protein-protein interactions come into play, which stabilize the enzyme in its active conformationref.			selective	tPA upregulates MMP-9 via LRP, causing degradation of neurovascular matrix integrity when given to stroke patients
alfimeprase (3–203 Fibrolase [3-Ser]), a recombinant fibrinolytic enzyme derived from fibrolase, with 3 disulfide bonds (Cys-116/196, Cys-156 /180, and Cys-158/163). Soluble alfimeprase is secreted by Pichia pastoris and a series of chromatography steps has been developed to generate pure material at Amgen. Alfimeprase differs from fibrolase in the amino-terminal region, where the amino-terminal three residues of fibrolase (Glu-Gln-Arg) were replaced with a single serine residue. The truncated analog was designed to prevent the formation of cyclized glutamine (pyroglutamic acid). Fibrolase and alfimeprase are similar with respect to thrombolytic activityref and are irreversibly bound by a2-macroglubulinref. The enzymes exhibit direct fibrinolytic activity without the activation of plasminogen, thus little hemorrhagic activity is observedref1, ref2. Because of their thrombolytic activity, low hemorrhagic response, and a2-macroglubulin binding, these enzymes have a high therapeutic potential for treating thrombotic disease. Alfimeprase is in a clinical trial for the treatment of peripheral arterial occlusionref.			selective
streptokinase (Streptase®) : it cleaves Arg560 on free plasminogen molecules to form free plasmin	1,500,000 IU in 60 seconds	18-24 hours	nonselective	allergic phenomena, systemic arterial hypotension
anistreplase / anisoylated plasminogen streptokinase activator complex (APSAC) (Eminase®) : Lys-plasminogen acylated at its catalytic-site Ser complexed to streptokinase	30-60 IU in bolus	110 hours	poorly selective	allergic phenomena
prourokinase / saruplase (Rescupase®) (single-chain)			nonselective
urokinase (Abbokinase®) (two-chain)	2,000,000 IU in 15 seconds	18 hours	poorly selective	high cost
heparin bound to dimeric FGF-2 / bFGF (dFGF2) leads to the dimerization of FGFR1 and activation of receptor tyrosine kinase : if given within 24 hours of a stroke, can limit the amount of brain tissue that is damaged. If given after 24 hours, it can substantially improve the patient’s rate of functional recovery, which the current treatment does not. Because dFGF2 can be given in small doses, it also reduces serious side effects, such as extreme weight loss, which patients have experienced in previous clinical studiesref			nonselective
ancrod, a natural defibrinogenating agent from snake venom, has proved to have a favourable effect when given within 3 h after an acute ischaemic strokeref

• serine proteases inhibitors (including plasmin inhibitors) : antifibrinolytic that act by competitively inhibiting plasminogen; they are used as a hemostatic in the treatment of severe hemorrhage associated with excessive fibrinolysis

• COX-1 inhibitors at doses lower than COX-2 IC₅₀ (expecially indobufen and acetylsalicylic acid as it is an irreversible inhibitor when given at 160-250 mg/day : platelets cannot re-synthetise COX-1 as they have no nucleus). COX-1 inhibition in platelets irreversibly impairs TxA₂ synthesis : on the contrary few ASA reaches endothelial cells thanks to liver catabolism and anyway inhibition of anti-platelet prostacyclin synthesis is reversible. Treatment has to be suspended at least 10 days before undergoing surgery. At doses > 100 mg/day only side effects increase, so that 75-100 mg/day are usually recommended : 200 mg/day are used only in AMI patients to increase the percentage of responders.

Disadvantages : unselective COX inhibitor, doesn't inhibit platelet aggregation and secretion
• calcium channel blockers (CCBs)
• adenosine transporter inhibitors (dipyridamole, sulfinpyrazone)
• thromboxan A₂ synthase inhibitors (picotamide, trapidil)
• phospholipase A₂ inhibitors => PGI₂ stimulators (cloricromene / AD6, a semi-synthetic coumarin derivative)
• P2_T antagonists (ticlopidine : 250 mg = 1 cps 2 times a day; clopidogrel : 75 mg = 1 cps a day (also an antiproliferative, preventing restenosis)

Pharmacodynamic response to clopidogrel, but not baseline platelet activity, was significantly associated with the CYP2C19 genotype : platelet aggregation in the presence of 10 µ mol/L ADP decreased gradually during treatment with clopidogrel 75 mg once daily in *1/*1 subjects, reaching 48.9± 14.9% on day 7 (p<0.0001 vs baseline), whereas it did not change in *1/*2 subjects (71.8± 14.6% on day 7, p=0.22 vs baseline, and p<0.003 vs *1/*1 subjects). Similar results were found with VASP phosphorylation. The CYP2C19*2 loss-of-function allele is associated with a marked decrease in platelet responsiveness to clopidogrel in young healthy male volunteers and may therefore be an important genetic contributor to clopidogrel resistance in the clinical setting^ref
Indications : patients with TIA or ischemic stroke in which ASA is not tolerated or effective
Side effects from ticlopidine : neutropenia, thrombocytopenia, diarrhea, transaminitis
• gpIIb/IIIa (integrins a