Alan D. Michelson, MD

Adenosine diphosphate, an important platelet agonist in vivo, has two types of receptors in the platelet plasma membrane: P2Y1 and P2Y12. The antiplatelet drugs ticlopidine (Ticlid, Roche Laboratories) and clopidogrel (Plavix, Sanofi Aventis/Bristol-Myers Squibb) are thienopyridines that are metabolized through cytochrome P450 in the liver. Thienopyridine metabolites, not the parent molecules, irreversibly antagonize the P2Y12 receptor. Ticlopidine has been largely replaced in clinical practice by clopidogrel because of the better side-effect profile of clopidogrel