DIMINISHED ANTIPLATELET EFFECT IN PATIENTS WITH TWO LOSS-OF-FUNCTION ALLELES OF THE CYP2C19 GENE. The effectiveness of Plavix results from its antiplatelet activity, which is dependent on its conversion to an active metabolite by the cytochrome P450 system, principally CYP2C19 [see WARNINGS AND PRECAUTIONS, CLINICAL PHARMACOLOGY]. No one thought it...