The Binding of Phenprocoumon to Human Plasma Proteins

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Abstract
By in vitro experiments with equilibrium dialysis and 5 .mu.g PPC[phenprocoumon]/ml an average of 99.7 .+-. 0.2% was bound to serum proteins. The binding in a solution with the albumin concentration which was present in the serum samples did not differ from this binding or from the binding in plasma where coagulation was prevented with either heparin or citrate. The binding constant in albumin solutions at 37.degree. C was 4.5 .+-. 0.3 l/mol .times. 10-5 and an average of 1.16 .+-. 0.04 primary binding sites were found. The association constant for the PPC albumin interaction was temperature dependent and the results of thermodynamic calculations suggested a combined ionic and non-polar type of binding, as the change in enthalpy contributed 40% of the change in free energy. A large positive entropy change was found (15.79 kcal/mol per .degree.K). The addition of phytomenadione to albumin solutions and of menadione to plasma caused a considerable decrease in the protein bound fraction of PPC, indicating the relevance of a study concerning the possible clinical consequences of the interactions.

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