DESCRIPTION

Clopidogrel, an antiplatelet agent structurally and pharmacologically similar to ticlopidine, is used to inhibit blood clots in a variety of conditions such as peripheral vascular disease, coronary artery disease, and cerebrovascular disease. Clopidogrel is sold under the name Plavix by Sanofi and Bristol-Myers Squibb. The drug is an irreversible inhibitor of the P2Y12 adenosine diphosphate receptor found on the membranes of platelet cells. Clopidogrel use is associated with several serious adverse drug reactions such as severe neutropenia, various forms of hemorrhage, and cardiovascular edema.

CHEMICAL FORMULA

C16H16ClNO2S

COMPOSITION

Clopidogrel (75mg)

INDICATION

For the reduction of atherosclerotic events (myocardial infarction, stroke, and vascular death) in patients with atherosclerosis documented by recent stroke, recent myocardial infarction, or established peripheral arterial disease.

PHARMACODYNAMICS

Since clopidogrel is a prodrug, it must be metabolized by CYP450 enzymes to produce the active metabolite that inhibits platelet aggregation. This active metabolite selectively inhibits adenosine diphosphate (ADP) binding to its platelet P2Y12 receptor and subsequently the ADP-mediated activation of the glycoprotein GPIIb/IIIa complex, thereby inhibiting platelet aggregation.

MECHANISM

The active metabolite of clopidogrel prevents binding of adenosine diphosphate (ADP) to its platelet receptor, impairing the ADP-mediated activation of the glycoprotein GPIIb/IIIa complex. It is proposed that the inhibition involves a defect in the mobilization from the storage sites of the platelet granules to the outer membrane. he drug specifically and irreversibly inhibits the P2Y12 subtype of ADP receptor, which is important in aggregation of platelets and cross-linking by the protein fibrin. No direct interference occurs with the GPIIb/IIIa receptor. As the glycoprotein GPIIb/IIIa complex is the major receptor for fibrinogen, its impaired activation prevents fibrinogen binding to platelets and inhibits platelet aggregation. By blocking the amplification of platelet activation by released ADP, platelet aggregation induced by agonists other than ADP is also inhibited by the active metabolite of clopidogrel.

ABSORPTION

Absorption is at least 50% based on urinary excretion of clopidogrel-related metabolites. Bioavailability has not been found to be affected by food.

METABOLISM

Hepatic, extensive and rapid, by hydrolysis to the main circulating metabolite, a carboxylic acid derivative, which accounts for approximately 85% of the circulating drug-related compounds. A glucuronic acid derivative of the carboxylic acid derivative has also been found in plasma and urine. Neither the parent compound nor the carboxylic acid derivative has a platelet inhibiting effect.

ELIMINATION

Following an oral dose of 14C-labeled clopidogrel in humans, approximately 50% of total radioactivity was excreted in urine and approximately 46% in feces over the 5 days post-dosing.

HALF LIFE

Carboxylic acid derivative: 8 hours (after single and multiple doses). Covalent binding to platelets has accounted for 2% of radiolabeled clopidogrel with a half-life of 11 days.

TOXICITY

A single dose of clopidogrel at 1500 or 2000 mg/kg was lethal to mice and rats, with 3000 mg/kg lethal to baboons. Symptoms included vomiting, breathing difficulty, hemorrhage, and prostration.