Recent theoretical work has suggested that radiochemical impurities can significantly alter the binding results for highly protein‐bound drugs. We compared protein binding of warfarin by ultrafiltration and equilibrium dialysis with 98% radiochemically pure [14C]warfarin. Ultrafiltration and equilibrium dialysis were performed at 37°C and pH 7.45 on the plasma of patients receiving chronic warfarin therapy. Binding to plasma from seven patients was measured in duplicate by both a nonspecific radioisotopic technique and a specific HPLC technique. The nonspecific technique gave percentage of free warfarin values of 1.84 ± 0.11 (mean ± SD) and 1.59 ± 0.14 for ultrafiltration and equilibrium dialysis, respectively. The HPLC procedure yielded a percentage of free warfarin by ultrafiltration of 0.969 ± 0.203 and a value of 0.690 ± 0.095 by equilibrium dialysis (p < 0.05). The HPLC procedure for protein binding was performed on plasma samples from 12 additional patients and yielded a percentage of free warfarin of 1.01 ± 0.69 by ultrafiltration and 0.44 ± 0.34 by equilibrium dialysis (p < 0.05). It can be concluded that radiochemical impurities may lead to significant overestimation of the percentage of free warfarin. Ultrafiltration yielded a higher percentage of free warfarin than did equilibrium dialysis, but the ability to distinguish binding differences among patients was similar.
- Plasma protein binding—methodological considerations, warfarin, radiochemical impurities
- Radiochemical impurities—methodological considerations, plasma protein binding of warfarin
- Warfarin—methodological considerations, plasma protein binding
ASJC Scopus subject areas
- Pharmaceutical Science