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Letter to the Editor
Editor, – The title of the Medicinal mishap 'Brand confusion with digoxin' (Aust Prescr 2006;29:153) was misleading. It unfairly blames the 'proliferation of new brands' for the error that was made.
The patient's usual medications included warfarin and digoxin 62.5 microgram (Lanoxin PG) but he was given 250 microgram tablets (Sigmaxin). He consequently suffered digoxin toxicity.
Brand proliferation is a fact of life and is not new. It is the basis of substantial cost-savings for individuals and for governments. All of the brands must be of good quality and must be interchangeable. In Australia, the Therapeutic Goods Administration undertakes checks during the registration process. Given that Lanoxin PG and Sigmaxin PG are marked as interchangeable brands of digoxin in the Schedule of Pharmaceutical Benefits, there was no error in dispensing a different brand, provided that the patient had consented and the prescriber had not checked the box on the prescription that reads 'Brand substitution not permitted'. The error in this case was selection of the wrong strength: Sigmaxin rather than Sigmaxin PG.
A better target for our wrath is the case of the Coumadin and Marevan brands of warfarin. The product information for the two brands states 'Do not interchange Coumadin and Marevan. Bioequivalence between these two brands of warfarin has not been established'. Clinical reports suggest these brands are not bioequivalent.1234 A pharmacoeconomic analysis concluded that use of one brand only is 'economically attractive'5given the costs of morbid events.
The argument that 'to withdraw one brand would seriously disadvantage those patients who are stabilised on it'6has been advanced for years and serves to perpetuate the current unsatisfactory situation. It's time to bite the bullet and withdraw one of these inequivalent brands of warfarin, even if short-term inconvenience results for some patients and their prescribers in the form of monitoring the changeover.
- Williams V, Vining R. Bioequivalence of Coumadin and Marevan [letter]. Aust Prescr 1998;21:60-3.
- Bolitho LE. Warfarin therapy [letter]. Aust Prescr 1999;22:103-5.
- Coumadin and Marevan are not interchangeable. Aust Adv Drug React Bull 1999;18:6.
- Dooley M. Recommendations for warfarin in Victorian public hospitals [letter]. Aust Prescr 2003;26:27-9.
- Mittman N, Oh PI, Walker SE, Bartle WR. Warfarin in the secondary prevention of thromboembolism in atrial fibrillation: impact of bioavailability on costs and outcomes. Pharmacoeconomics 2004;22:671-83.
- Your questions to the PBAC: warfarin tablets. Aust Prescr 1996;19:6-7.