Describe the structure and function of platelets (50% marks). Outline the pharmacology of clopidogrel (50% marks).
Platelets are small cells in blood, approximately 150,000 – 300,000 / microliter of blood with a
half life of approximately 4 days. They have important membrane receptors (for collagen, vWF
and fibrinogen) and intracellular contents (Actin, Myosin, Glycogen, Lysosomes, Dense granules,
Alpha granules) and are involved in forming a platelet plug and clotting. Common omissions were
to not give a normal platelet count or half life. Diagrams of the clotting cascade were not required.
Clopidogrel is an oral, thienopyridine class antiplatelet agent (a prodrug activated in the liver by
cytochrome P450 enzymes), used to inhibit blood clots in coronary artery disease, following stent
placement, peripheral vascular disease, and cerebrovascular disease. Mechanism of action is:
specifically and irreversibly inhibits the P2Y12 subtype of ADP receptor, which is important in
aggregation of platelets and cross-linking by the protein fibrin and thus platelet aggregation,
which is inhibited when binding blocks activation of the glycoprotein IIb/IIIa pathway. Elimination
half-life of about 8 hours; rapidly absorbed after oral administration; undergoes rapid hydrolysis in
liver and renal excretion; 95% protein bound. Important interactions/precautions include proton
pump inhibitors, phenytoin, warfarin, heparin, danaparoid, enoxaparin and various thrombolytics.
Greatest risk is bleeding. The best answers had a structured approach to describing a drug.