Early overanticoagulation with acenocournarol due to a genetic polymorphism of cytochrorne P450CYP2C9

We report the case of a young healthy woman who presented an early overanticoagulation when receiving acenocoumarol for a first thromboembolic episode. The patient had none of the risk factors known to influence the response to the coumarinic derivative except that she carried the rare *3 allelic variant of the cytochrome P450 CYP2C9 in a homozygous status. This case illustrates the role of the *3 polymorphism of the cytochrome P450 CYP2C9 as an independent risk factor modulating the sensitivity of patients to the anticoagulant effect of aceno-coumarol. The usefulness of CYP2C9 genotyping before starting coumarinic treatments is discussed. (C) 2003 Lippincott Williams Wilkins.