Aim: Warfarin is the most frequently prescribed antithrombotic agent, available in Australia as brands Coumadin and Marevan. Although both are manufactured by Aspen Pharmaceuticals, there are differences in formulation. The product information states they cannot be used interchangeably. Two incident reports of warfarin brand interchange in our hospital prompted a literature review. We aimed to review published evidence on the pharmacokinetics and bioequivalence of different warfarin brands and make brand switching recommendations. Methods: Systematic review of the literature on warfarin bioequivalence and incidents reported by the Therapeutic Goods Administration (TGA). Results and discussion: Fifteen studies explored different warfarin formulations. No significant differences were found in efficacy with brand switching in eight studies analysing participants who were healthy, had atrial fibrillation (AF), or a mechanical heart valve. Prospective observational studies demonstrated no significant difference in the International Normalised Ratio (INR) or adverse events, however, a retrospective observational study demonstrated an increase in complications. Of the four population studies, only one demonstrated elevated rates of haemorrhage or thrombosis. No studies directly compared Coumadin and Marevan. Three TGA case reports describe adverse events from brand switching. Conclusion: Studies of different warfarin formulations demonstrate bioequivalence in population studies, but with marked inter-individual variation, hence the recommendation is to continue the same brand of warfarin where possible. However, brand switching is preferable to withholding a dose of warfarin for inpatients, in the absence of the patient’s usual brand. If substituting or brand switching, close monitoring with frequent INR testing is suggested.
|Pages (from-to)||22 - 28|
|Number of pages||7|
|Journal||Australian Medical Student Journal|
|Publication status||Published - 2016|