Clopidogrel, CYP2C19, and a Black Box.

Area of Science:

• Pharmacology
• Drug Metabolism
• Cardiovascular Medicine

Background:

• Clopidogrel metabolism was presumed to be primarily via CYP2C19.
• This led to concerns about drug interactions with CYP2C19 inhibitors like proton pump inhibitors (PPIs).
• A FDA "Black Box" warning was issued in 2010 based on early in vitro and ex vivo studies.

Purpose of the Study:

• To re-evaluate the primary metabolic pathway of clopidogrel.
• To reconcile in vitro findings with clinical observations regarding clopidogrel and PPI co-administration.
• To investigate the discrepancy between presumed CYP2C19 metabolism and clinical outcomes.

Main Methods:

• Revisiting in vitro drug metabolism studies using "Supersomes".
• Conducting new in vitro metabolism studies using hepatosomes, which better reflect native cytochrome P-450 enzyme expression.
• Analyzing data from prospective clinical studies (e.g., COGENT) and meta-analyses.

Main Results:

• In vitro studies using hepatosomes confirmed clopidogrel is primarily a CYP3A substrate.
• This finding aligns with clinical data showing no increased risk of major adverse cardiovascular events (MACE) with concomitant clopidogrel and PPI use.
• The absence of a significant interaction contradicts the initial presumption of CYP2C19 involvement.

Conclusions:

• Clopidogrel's primary metabolism is via CYP3A, not CYP2C19.
• The lack of interaction between clopidogrel and PPIs is explained by clopidogrel's actual metabolic pathway.
• Further research may explore the role of CYP2C19 in specific patient populations with reduced function alleles.