The use of generic drugs has become increasingly common in clinical practice. However, for drugs with a narrow therapeutic index such as warfarin (Coumadin), there may be some concern regarding the definition of bioequivalence.

Warfarin is a commonly used anticoagulant with clearly documented benefits. However, as a drug with a narrow therapeutic index, only a small dosing range separates warfarin’s therapeutic effect from toxicity in patients and appropriate dosing is critical.

Due to conflicting results previously observed in clinical studies comparing brand name and generic warfarin products the authors performed a systematic review of the literature to better assess the characteristics of generic warfarin products.

Eleven studies including more than 40,000 patients were included, five were randomized controlled trials, and six were observational studies.

In the five randomised controlled trials no statistically significant difference was found between patients randomly assigned to receive brand name or generic warfarin.

The results of the observational studies were more conflicting, however the overall results of the systematic review suggest that generic warfarin products may be as safe and effective as brand name products and that patients may be safely treated with these products. The authors did, however, recommend closer monitoring when switching brands, as variations in individual INR (international normalised ratio) response may be seen. They also recommended for patients to avoid switching too often in order to allow the development of a stable warfarin dosage.

Reference

1. Dentali F, Donadini MP, Clark N et al. Brand Name versus Generic Warfarin A Systematic Review of the Literature. Pharmacotherapy. 2011;31(4):386-93.