Consequences of the N-B transition of albumin for the binding of warfarin in human serum.

The protein binding of warfarin in serum has been studied by means of circular dichroism and equilibrium dialysis. Evidence was found that the N-B transition of albumin, occurring around physiological pH, takes place not only in solutions of pure albumin but also in serum. The protein binding of warfarin in serum is pH-dependent and increases with pH especially around physiological pH. This pH-dependent serum binding of warfarin can be reasonably explained by the N-B transition of albumin. The effect of Ca2+ and Mg2+ on the protein binding of warfarin in serum is negligible at pH 7.4, whereas at this pH Cl- increases the free-warfarin concentration by a competitive displacement.