Because Plavix inhibits CYP2C9 at high doses, it may interfere with the metabolism of drugs processed by the liver enzyme CYP2C9, and individuals with CYP2C9 SNP variants that encode lower metabolizers to begin with would presumably be at greater risk for such side-effects when taking Plavix at the same time as drugs metabolized by CYP2C9.
SNPs influencing the metabolism (or effectiveness) of Plavix include:
- rs4244285: patients who are prescribed Plavix and who carriers of this CYP2C19*2 SNP are at 3-4x increased risk for heart attacks or other adverse cardiovascular events [PMID 19108880][PMID 19106083][PMID 19106084]
This has now (2010) been acknowledged by the FDA, who have added a boxed warning to Plavix, alerting patients and health care professionals that the drug can be less effective in people who have CYP2C19 variants and cannot convert the drug as effectively to its active form.
News: Heart stent patients with a CYP2C19 mutation may wish to consider using prasugrel (Effient) or ticagrelor (Brilinta) instead of clopidogrel (Plavix) according to a 2018 study noting a reduction from 27% to 8% in heart attack or stroke incidence.