Herbal drug related warfarin intoxication

Abstract

Warfarin is a widely used antithrombotic drug in prevention of both arterial and venous thrombosis. Glucosamine is a popular dietary supplement used in symptomatic treatment of osteoarthritis. The interaction mechanism between these two drugs is not known yet. 63 year old woman, who was taking warfarin therapy 5 mg /day for 5;months for pulmonary embolism (therapeutic INR range:2.0–3.0), visited the emergency room with haematuria and rash. She had synchronous breast and colonic tumours for which right mastectomy and right hemicolectomy were done 5 months ago. Her INR (Internatıonal Normalized Ratio) values were highly increased (12.5) due to consumption of a herbal drug involving glucosamine hydrochloride 250 mg , boswellia extract and grapefruit extract at that day for arthralgia. Boswellia extracts are used in management of osteoarthritis. Naranjo adverse drug reaction probability scale score was 6, which indicated a probable relationship between the patient’s elevated INR and use of two drugs (warfarin and herbal drug) at the same time. After discontinuation of both drugs, two units of fresh frozen plasma were given. Her INR reduced to 2.5; as a result haematuria and rash regressed. This case report suggests a potential interaction between warfarin and both glucosamine and grapefruit extract. The inhibitory effect of grapefruit extract on cytochrome P450 isoenzymes is combined with the effect of glucosamine. Clinicians should be aware of patients taking herbal medicines with such drugs like warfarin which has narrow therapeutic index.