Influence of fatty acids on the binding of warfarin and phenprocoumon to human serum albumin with relation to anticoagulant therapy.

Warfarin and phenprocoumon binding to human serum albumin was studied by equilibrium dialysis. The first stoichiometric binding constant was 1.89 x 10(5) M-1 for warfarin and 2.40 x 10(5) M-1 for phenprocoumon. The affinity of warfarin was markedly increased on addition of up to 3 mol mol-1 albumin of palmitic, stearic, oleic or linoleic acids with energetic couplings for co-binding of one molecule of each of the fatty acids and one molecule of warfarin of 0.9, 1.1, 0.7 and 0.6 kJ mol-1, respectively. The affinity of phenprocoumon was only increased slightly on addition of palmitate with an energetic coupling of 0.3 kJ mol-1. Six consecutive serum samples were obtained from each of 14 patients undergoing surgery. The serum affinity of the drugs varied considerably corresponding to free drug concentrations between 0.7 and 2.7% for warfarin and between 0.8 and 4.9% for phenprocoumon. The affinity of warfarin but not of phenprocoumon was correlated to the increasing plasma fatty acid concentration. Anticoagulant therapy with phenprocoumon may thus be less sensitive than warfarin to changes in the fatty acid concentration of plasma.