Whether generic and proprietary wrafarin is interchangeable has been investigated. Multiple n-of-1 randomized, double-blind, crossover trials switched outpatients (N = 7) between a generic warfarin formulation (Apo-warfarin) and Coumadin over 30 weeks. Study patients took each drug for five 3-week periods, with international normalized ratio (INR) measurements taken twice per period. Inter- and intrapatient differences between generic warfarin and Coumadin were compared, and overall study patient results were compared with those of a Coumadin control group.
There were no differences between warfarin products in terms of mean INR results or number of dosage adjustments required. There also was no difference in INR variation based on warfarin formulation (p > 0.69), nor was a patient and warfarin interaction found (p > 0.81). The INR results were not influenced by whether patients were maintained on Coumadin only (control group) or interchanged between Coumadin and generic warfarin (p = 0.98). Bongiorno RA, Nutescu EA. Generic warfarin: implications for clinical practice and perceptions of anticoagulation providers. Semin Thromb Hemost. 2004;30:619-626.
Halkin H, Shapiro J, Kurnik D, Loebstein R, Shalev V, Kokia E. Increased warfarin doses and decreased international normalized ratio response after nationwide generic switching. Clin Pharmacol Ther. 2003;74:215-221.
Witt DM, Tillman DJ, Evans CM. Evaluation of the clinical and economic impact of a brand name-to-generic warfarin sodium conversion program. Pharmacotherapy. 2003;23:360-368.
Jennifer A Pereira et al, Are Brand-Name and Generic Warfarin Interchangeable? Multiple N-of-1 Randomized, Crossover Trials The Annals of Pharmacotherapy: Vol. 39, No. 7, pp. 1188-1193.