Fatal drug interaction between cholestyramine and phenprocoumon.

We describe a patient with a prosthetic aortic valve who developed fatal valve thrombosis due to an interaction between phenprocoumon and cholestyramine. The general practitioner who had prescribed cholestyramine was aware of a potential interaction between these two drugs and the patient ingested cholestyramine exactly according to the rules of the manufacturer (>1 h before phenprocoumon). However, due to enterohepatic cycling and the long half-life of phenprocoumon, an interaction between these two drugs could not be avoided. We therefore recommend that cholestyramine not be administered to patients treated with drugs undergoing enterohepatic cycling, such as oral anticoagulants.