Warfarin and warfarin-alcohol levels in anticoagulated patients

The relationship between dosage, prothrombin ratio, and steady-state plasma concentrations of warfarin and warfarin-alcohol, were determined in 43 patients regularly attending an anticoagulant clinic. The warfarin and warfarin-alcohol concentrations were determined by a gas chromatographic mass spectroscopic (GC/MS) method. A significant correlation was found between the dose and the plasma level of warfarin. There was no significant correlation between the prothrombin ratio and the dose of warfarin, the steady-state plasma levels of warfarin or warfarin-alcohol, or the sum of their plasma concentrations. Measurement of the plasma levels of warfarin and warfarin-alcohol is likely to be of little help clinically other than to detect failure of compliance or malabsorption.