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Subtherapeutic INR values associated with a switch to generic warfarin
1Department of Pharmacy Practice, College of Pharmacy, University of Oklahoma, Oklahoma City 73190, USA.
The Annals of Pharmacotherapy
|February 24, 2001
Summary
Switching from Coumadin to generic warfarin may cause international normalized ratio (INR) fluctuations. Close INR monitoring is crucial after brand changes to ensure therapeutic anticoagulation.
Area of Science:
- Pharmacology
- Clinical Pharmacy
Background:
- Warfarin (Coumadin) is a narrow therapeutic index anticoagulant.
- Generic warfarin was approved by the FDA in 1997.
- Bioequivalence studies exist between brand and generic warfarin.
Observation:
- Two cases showed subtherapeutic INR values after switching from Coumadin to generic warfarin.
- All other variables were kept consistent in these cases.
- This highlights potential INR fluctuations during brand transitions.
Findings:
- Despite FDA bioequivalence, brand and generic warfarin may have different content uniformity.
- Differences in specifications between Dupont Pharma and USP can affect drug content.
- Switching between warfarin formulations can lead to significant INR changes.
Implications:
- Patients switching between Coumadin and generic warfarin require closer INR monitoring.
- Dose adjustments may be necessary due to potential INR variability.
- Careful patient management is essential to maintain therapeutic anticoagulation.