Warfarin brands

Although a comprehensive guide to managing warfarin, the article in the April 2015 issue (Aust Prescr 2015;38:44-8) did not mention the problem of brand confusion with warfarin. Transition of care, such as hospital admission, is a time when warfarin management may be compromised. In Australia we have two brands − Coumadin and Marevan. Both are manufactured by Aspen Pharmaceuticals, and are available in different strengths and tablet colours. Recently reported incidents involving warfarin brand confusion at our hospital resulted in dose omissions due to Marevan not being available on the ward and inadvertent switching from Marevan to Coumadin. Although no patient harm resulted, time was spent in sourcing the ‘right’ brand and managing the incidents.

The Pharmaceutical Benefits Scheme notes that the brands have not been shown to be bioequivalent and should not be interchanged.¹ However, a systematic review comparing the bioequivalence of six international warfarin brands found that switching brands was relatively safe.² In 44 years of reporting adverse drug reactions in Australia, only three reports, all from 1977, implicate brand switching.³

The manufacturer has previously been approached to phase out one brand, with a recommendation that Coumadin be primarily used.⁴ We call for either bioequivalence testing of Coumadin and Marevan by the manufacturer or, in the interests of medication safety, for only one brand of warfarin to be available.

Linda Graudins
Senior medication safety pharmacist
Alfred Hospital

Fiona Chen
Medical student
Monash University

Ingrid Hopper
Honorary clinical pharmacologist
Alfred Hospital
Melbourne

Philip A Tideman, Rosy Tirimacco, Andrew St John and Gregory W Roberts, authors of the article, comment:

We agree that brand continuity for warfarin is preferred. While it seems unlikely there would be clinically significant differences in the two brands, which vary by a single excipient, there has been no formal bioequivalence testing. The availability of a single brand in Australia would simplify warfarin management and remove any confusion about brand swapping for both patients and clinicians.