Hypoprothrombinemia in naproxen overdose.

Transient prolongation of the prothrombin time was observed in the setting of a 10-g overdose of naproxen. The patient reported was previously healthy, without chronic liver disease, bleeding disorders, or malnutrition. The most likely mechanism for this effect is direct inhibition of the synthesis of vitamin-K-dependent clotting factors, possibly via production of "abnormal" prothrombin.