Effects of oxametacin on coumarin anticoagulation and on platelet function in humans.

In 12 chronically anticoagulated patients the administration of 1-p-chlorobenzoyl-5-methoxy-2-methyl-3-indoacetohydroxamic acid (oxametacin, Flogar), three times 100 mg a day, decreased the thrombotest percentage from a mean of 11.2% to a mean of 8.3% after one week and of 7.8% after two weeks of treatment. A potentiating effect of oxametacin was also found when the prothrombin time or the activated partial thromboplastin time were used as parameters. In one third of our patients an adaptation of the coumarin dose or even an interruption in the warfarin administration was necessary. Although no severe bleedings occurred, care should be taken in prescribing oxametacin to anticoagulated patients. In a second part of this study we compared the ex vivo effects of a single oral dose of 1 g of acetylsalicylic acid, 50 mg of indometacin and 100 mg of oxametacin in human volunteers. Platelet aggregation and 5HT--14C release induced by collagen. Thrombofax, ADP, adrenaline (epinephrine), bovine plasma and ristocetin were measured before, 1 and 24 h after drug administration. A clear-cut inhibitory effect as induced by acetylsalicylic acid was not found for oxametacin.