A few reports suggest that glucosamine with or without chondroitin may increase INR in patients taking warfarin
Clinical evidence,mechanism, importance and management
A 69-year-old man stabilised on warfarin 47.5mg weekly had an increase in his INR from 2.58 to 4.52 four weeks after starting to take 6 capsules of Cosamin DS (glucosamine hydrochloride 500 mg,sodium chondroitin sulfate 400 mg, manganese ascorbate per capsule) daily. His warfarin dose was reduced to 40mg weekly, and his INR returned to target range of 2 to 3 (INR 2.15) with continued Cosamin DS therapy (See reference number 1). A comment on this report noted that this is twice usual dose of glucosamine (See reference number 2). The Canadian Adverse Drug Reaction Monitoring Program briefly reported that an increase in INR had been noted when glucosamine was given to patients on warfarin,and that INR values decreased when glucosamine was stopped (See reference number 3). Moreover, in 2006 CHM in UK reported that they had received 7 reports of an increase in INR in patients taking warfarin after they started taking glucosamine supplements (See reference number 4).
In contrast,a 71-year-old man stabilised on acenocoumarol 15mg weekly had a decrease in his INR to 1.6 after taking glucosamine sulfate (Xicil) 1.5 g daily for 10 days. The glucosamine was stopped and INR reached 2.1. When glucosamine was restarted, with an increase in acenocoumarol dose to 17mg weekly, INR only reached 1.9. The glucosamine was eventually stopped (See reference number 5).
There do not appear to have been any controlled studies of effects of glucosamine supplements on pharmacodynamics or pharmacokinetics of oral anticoagulants. The cases described suggest it would be prudent to monitor INR more closely if glucosamine is started. If a patient shows an unexpected change in INR, bear in mind possibility of self-medication with supplements such as glucosamine. Note that CHM in UK recommend that patients taking warfarin do not take glucosamine (See reference number 4).
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Canadian Adverse Drug Reaction Monitoring Program. Communiqué. Warfarin and glucosamine: interaction. Can Adverse Drug React News (2001) 11 (Apr),8.
Commission on Human Medicines/Medicines and Healthcare Products Regulatory Agency.Glucosamine adverse reactions and interactions. Current Problems (2006) 31,8.
Garrote García M,Iglesias Piñeiro MJ, Martín Álvarez R, Pérez González J. Interacción farmacológica del sulfato de glucosamina con acenocumarol. Aten Primaria (2004) 33, 162–4.