Could hawthorn increase the anticoagulant effect of warfarin?/nA 61-year-old man treated with warfa

Fråga: Could hawthorn increase the anticoagulant effect of warfarin?

A 61-year-old man treated with warfarin for atrial fibrillation has started medicating with hawthorn (Crataegus sp.). After the hawthorn treatment was initiated, his PK-INR has increased from 2.8 to 3.9.

Sammanfattning: Theoretically, hawthorn could interact pharmacologically with warfarin and there is no documentation supporting the safety or effectiveness of co-treatment with the two drugs. Hence, we recommend that use of hawthorn is avoided in patients treated with warfarin.

Svar: Hawthorn is thought to possess cardiotonic, coronary vasodilator and hypotensive properties and has traditionally been used for cardiac insufficiency, paroxysmal tachycardia, hypertension and arteriosclerosis (1).

We found no reports of an interaction between hawthorn and oral anticoagulants in Drugline, Medline or standard pharmacological literature. In vitro, hawthorn inhibits thromboxane A2 synthesis (2). Hence, it could theoretically hamper platelet aggregation and increase the bleeding risk in patients treated with antiplatelet agents or anticoagulants (2). However, this mechanism would not involve the synthesis of coagulation factors and should not alter the PK-INR.

Medication with hawthorn has been associated with an increased absorption of digoxin (1), but this may be of little relevance for warfarin, since the pharmacokinetics of the two drugs are quite different. No reports of interactions with drugs other than digoxin were identified, but this could very well be due to a general lack of documentation and should not be interpreted as a low over-all propensity for pharmacological interactions. Barnes J, Anderson LA, Phillipson JD. Herbal medicines. A guide for healthcare professionals. 3rd ed. London: The Pharmaceutical Press; 2007 MICROMEDEX(R) Healthcare Series: Thomson MICROMEDEX, Greenwood Village, Colorado (cited 2008-08-08)