[Beware: propafenon potentiates the effect of oral anticoagulants].

In a 68 years old female patient with premature ventricular contractions who was treated with phenprocoumon (Marcumar) because of pulmonary infarction, propafenon (Rytmonorm)--a new anti-arrhythmic drug--lead to an increased effect of coumarin. Inspite of pausing with coumarin for eight days the low Quick rates (less than 15%) did not increase until propafenon was stopped. Afterwards the coumarin treatment was continued with 1,5 to 3 mg a day. In case of a combined treatment with propafenon and coumarin Quick rates should be controlled frequently.