Generic Clopidogrel: Has Substitution for Brand Name Plavix® Been Effective?

Background: Following the expiration of brand name exclusivity of Plavix® in 2012, generic clopidogrel bisulfate was approved. As a widely prescribed medication with significant inter-patient pharmacokinetic and pharmacodynamic variability, data regarding the impact of switching to generic clopidogrel bisulfate on patients is needed. Objective: The objective of this study was to determine whether generic clopidogrel bisulfate is as efficacious as Plavix® for the inhibition of platelet aggregation. Methods: Patients treated with Plavix® monotherapy (n = 254) or generic clopidogrel bisulfate monotherapy (n = 185) were included in this retrospective review. Confounding factors previously found to affect clopidogrel responsiveness (diabetes, female sex, and smoking) were assessed, as well as medications classified as substrates, inducers, and inhibitors of enzymes involved in clopidogrel metabolism. Whole blood impedance aggregometry was used to measure platelet aggregation in response to adenosine diphosphate. Patients were tested after ≥2 weeks of treatment and designated as non-responders if aggregation response exceeded sensitivity thresholds of 6 ohms of impedance. Results: The introduction of generic clopidogrel bisulfate was associated with a decrease in antiplatelet resistance (44% to 31%, p < 0.01) and decreased mean ohms of resistance (5.06 ± 4.55 to 3.32 ± 4.03, p < 0.01). Prior to analysis of secondary outcomes, 217 patients were eliminated due to antiplatelet usage for longer than 3 years (n = 123 for Plavix® and n = 118 for clopidogrel). There was no statistically significant finding in prevalence of secondary events. Conclusion: Resistance rates to the antiplatelet, clopidogrel are significantly lower since the switch to generic formulations. Further investigation into the impact of variability between clopidogrel bisulfate formulations is needed.