Clinical evidence,mechanism, importance and management
A woman taking warfarin for atrial fibrillation whose INR was normally within range 2 to 3 had a modest rise in her INR to 3.4, apparently due to use of 10 drops of boldo after meals and one capsule of fenugreek before meals. A week after stopping these two herbal medicines her INR had fallen to 2.6. When she restarted them,her INR rose to 3.1 after a week,and to 3.4 after 2 weeks. Her INR was later restabilised in her normal range in presence of these two medicines by reducing warfarin dosage by 15 % (See reference number 1). The mechanism of this apparent interaction remains unknown,and it is not known whether both herbs or just one was responsible for what happened. Boldo comes from Peumus boldus, and might have antiplatelet activity,and fenugreek comes from Trigonella foenumgraecum, which might contain coumarins (but see Coumarins + Herbal medicines interaction, above).
This patient had no undesirable reactions (e.g. bruising or bleeding), but this case serves to draw attention to possibility of an interaction in other patients taking anticoagulants if these herbal medicines are also taken.
1. Lambert JP,Cormier A. Potential interaction between warfarin and boldo-fenugreek. Pharmacotherapy (2001) 21, 509–12.