The effect of daily administration of naproxen on the prothrombin complex activity in patients under long-term therapy with phenprocoumon.

Out of a total of 150 patients attending an out-patient clinic for anticoagulant therapy, 12 had disorders which normally would indicate a prolonged use of an antirheumatic drug. To 6 of these patients, naproxen (1/4 g twice daily) was given while anticoagulant treatment with phenprocoumon was continued in an unchanged dosage schedule (average dose 2.1 mg/day). On the average, the prothrombin complex activity (PP%) was reduced to a stable level 10--20% below that obtained during a 2-month period before the naproxen treatment was started. No bleeding episodes or other effects were observed. Thus the simultaneous administration of naproxen caused no problems for the maintenance of a stable anticoagulant therapy.