Effect of Pirprofen on Protein Binding of Warfarin and Tolbutamide in Human Plasma

The extent of warfarin and tolbutamide binding to plasma proteins was determined with and without pirprofen by an ultrafiltration procedure employing14C‐labeled drugs. Results fromin vitrostudies at 37° showed that the degree of binding amounted to 97.8% for warfarin and 95.6% for tolbutamide. The binding characteristics of these drugs were not altered when plasma containing either warfarin or tolbutamide at concentrations equivalent to those expected normally after therapeutic dosing were concomitantly spiked with therapeutic amounts of pirprofen. Consequently, potentiation resulting from drug displacement would not be anticipated in humans when pirprofen is administered along with warfarin or tolbutamide.