Generic Name for Coumadin
Warfarin is the generic name for Coumadin. Both contain the same active pharmaceutical ingredient—warfarin sodium—which is a racemic mixture of R- and S-enantiomers that functions as a vitamin K antagonist anticoagulant 1, 2.
Chemical and Pharmacologic Identity
- Warfarin sodium is chemically described as 3-(α-acetonylbenzyl)-4-hydroxycoumarin, with molecular formula C19H15NaO4 2
- The drug is a coumarin derivative that produces anticoagulation by inhibiting vitamin K epoxide reductase, thereby preventing the cyclic interconversion of vitamin K and its 2,3 epoxide 1, 2
- This mechanism blocks the γ-carboxylation of vitamin K-dependent clotting factors (II, VII, IX, and X), resulting in partially decarboxylated proteins with reduced coagulant activity 1
Brand vs. Generic Interchangeability
Generic warfarin products are considered bioequivalent to brand-name Coumadin and can be safely interchanged in most patients, though closer INR monitoring during the transition period is prudent 3.
Evidence Supporting Interchangeability:
- A systematic review of 11 studies involving over 40,000 patients found no statistically significant differences in mean INR values, magnitude of dosage changes, time in therapeutic range, or rates of thromboembolic/hemorrhagic complications between brand-name and generic warfarin 3
- Multiple n-of-1 randomized crossover trials demonstrated no differences in mean INR results, number of dosage adjustments required, or INR variation when patients were switched between Coumadin and generic warfarin (Apo-warfarin) 4
- A prospective observational study of 182 HMO patients switching from Coumadin to Barr generic warfarin found no significant changes in INR control, frequency of monitoring, dose changes, or adverse events 5
Important Caveats:
- Individual patient INR responses may vary when switching between formulations, as warfarin has a narrow therapeutic index where small changes in systemic concentration can lead to significant pharmacodynamic variation 6, 3
- Case reports have documented subtherapeutic INR values in some patients after switching from Coumadin to generic warfarin, necessitating dose adjustments 6
- The FDA approved generic warfarin based on standard bioequivalence criteria, but content uniformity specifications may differ slightly between manufacturers 6
Clinical Management Recommendations
- When switching between brand-name Coumadin and generic warfarin (or between different generic manufacturers), increase INR monitoring frequency for 2-4 weeks 6, 3
- Maintain the same dosing schedule initially, but be prepared to make dose adjustments based on INR results 6
- Educate patients that both formulations contain the same active ingredient and work through identical mechanisms 1, 2
- The S-enantiomer of warfarin (which is 2-5 times more pharmacologically active than the R-enantiomer) is metabolized primarily by CYP2C9, and genetic polymorphisms in this enzyme affect dose requirements regardless of whether brand or generic formulation is used 7, 2