Increased risk of atherothrombotic events associated with cytochrome P450 3A5 polymorphism in patients taking clopidogrel

Abstract

Background: Clopidogrel is a prodrug requiring metabolism by cytochrome P450 3A (CYP3A) isoenzymes, including CYP3A5, in order to be active. It is controversial whether clopidogrel interacts with CYP3A inhibitors. We investigated the influence of CYP3A5 polymorphism on the drug interaction of clopidogrel.

Methods: In phase 1 of the study, we administered clopidogrel to 16 healthy volunteers who had the CYP3A5 non-expressor genotype (*3 allele) and 16 who had the CYP3A5 expressor genotype (*1 allele) with and without pretreatment with itraconazole, a potent CYP3A inhibitor. A platelet aggregation test was performed at baseline, 4 hours, 24 hours and 6 days after clopidogrel administration. In phase 2, we compared clinical outcomes of 348 patients treated with clopidogrel after successful coronary angioplasty with bare-metal stent implantation according to their CYP3A5 genotype; the primary end point was a composite of atherothrombotic events (cardiovascular death, myocardial infarction and non-hemorrhagic stroke) within 1 and 6 months after stent implantation.

Results: In phase 1, the change in platelet aggregation after clopidogrel administration and pretreatment with itraconazole was greater among the subjects with the CYP3A5 expressor genotype than among those with the non-expressor genotype: 24.9% (standard deviation [SD] 13.9%) v. 6.2% (SD 13.5%) at 4 hours (p < 0.001); 27.7% (SD 16.5%) v. 2.5% (SD 8.3%) at 24 hours (p < 0.001); and 33.5% (SD 18.6%) v. 17.8% (SD 13.8%) at day 7 (p < 0.01). In phase 2, atherothrombotic events occurred more frequently within 6 months after stent implantation among the patients with the non-expressor genotype than among those with the expressor genotype (14/193 v. 3/155; p = 0.023). Multivariable analysis showed that the CYP3A5 polymorphism was a predictor of atherothrombotic events in clopidogrel users.

Interpretation: People with the CYP3A5 non-expressor genotype are vulnerable to drug interactions between clopidogrel and CYP3A inhibitors. This phenomenon may be associated with worse outcomes in patients with the non-expressor genotype who are given clopidogrel after coronary angioplasty and implantation of bare-metal stents.

Fig. 1: A: Adenine diphosphate (ADP) is an important physiologic agonist that plays a vital role in normal hemostasis and thrombosis. The P2Y₁₂ receptor of platelets signals through a Galpha i coupled G-protein receptor (Gi₂ coupled) and is important for potentiation of platelet activation mediated by other physiologic agonists, including collagen, von Willebrand factor and thromboxane A₂.¹⁸ B: Inhibition of ADP-induced platelet aggregation by clopidogrel. Clopidogrel is a prodrug requiring metabolism by cytochrome P450 (CYP) 3A isoforms in order to be active. The active metabolite of clopidogrel blocks the platelet's P2Y₁₂ receptor.¹⁹ Note: cAMP = cyclic adenosine monophosphate. Photo by: Lianne Friesen and Nicholas Woolridge

Fig. 2: A: Cytochrome P450 (CYP) 3A4 and CYP3A5 are major isoforms of the CYP3A system. Total CYP3A activity accounts for 20% of all phase I reactions in the liver and metabolizes more than 50% of drugs. Under usual conditions, where both CYP3A4 and CYP3A5 contribute to total CYP3A activity, CYP3A4 is probably the main contributor. Therefore, the antiplatelet activity of clopidogrel may not differ substantially between patients with the CYP3A5 expressor genotype and those with the non-expressor genotype. B: In the presence of multiple substrates or inhibitors, CYP3A4 is more easily inhibited than CYP3A5, and therefore CYP3A5 becomes the main contributor to total CYP3A activity. In this condition, total CYP3A activity would differ depending on the patient's CYP3A5 genotype. Photo by: Lianne Friesen and Nicholas Woolridge

Fig. 3: Platelet aggregation in healthy volunteers taking clopidogrel, by CYP3A5 genotype (non-expressor v. expressor).

Fig. 4: Change in platelet aggregation from baseline after administration of clopidogrel, by CYP3A5 genotype.

Fig. 5: Platelet aggregation in healthy volunteers taking clopidogrel after pretreatment with the CYP3A inhibitor itraconazole. NS = not significant.

Fig. 6: Change in platelet aggregation from baseline after administration of clopidogrel and pretreatment with itraconazole.