Editor, – We have recently had several patients who have experienced clinically significant haemorrhages whilst on warfarin. Two of these incidents occurred in patients who had been on stable doses of long-term warfarin but then suddenly developed unexplained elevations in the results of their INR tests. One of these incidents was possibly due to mixing warfarin 2 mg and 3 mg tablets from different brands (Coumadin and Marevan). This can occur when patients are admitted to our Base hospital; they are only allowed to take one brand of warfarin as the other is not in the hospital formulary.
I have been attempting to unravel the statements from Boots Healthcare that 'the bioequivalence of the various strengths of warfarin manufactured in Australia under the Marevan and Coumadin brand names has never been tested rather than they are not bioequivalent' and 'the formulation and manufacturing methods are significantly different' (Aust Prescr 1997;20:33).
Patients taking warfarin have a relatively high incidence of adverse reactions- mainly haemorrhage - and patient safety issues should be considered of primary importance. The company should therefore be encouraged to standardise the bioequivalence of their products - or remove one brand from production - as there are overlapping products available (Marevan 1 mg, 3 mg, 5 mg and Coumadin 1 mg, 2 mg, 5 mg).
Leslie E. Bolitho
Consultant Physician in Internal Medicine
Wangaratta, Vic.
