Mefenaminic acid binding by blood plasma and organ homogenates

: Concerns the spectrophotometric method for microdetermination of total and unbound mefenaminic acid in biological material. The method has been developed on the basis of stained complex formation. Mefenaminic acid binding to plasma proteins and organ homogenates has been studied in vitro and in vivo experiments and by the methods of equilibrium dialysis and fluorescence. The rate of drug binding to plasma proteins amounts to 75 +/- 5%. The highest binding capacity is shown by the plasma, liver and kidneys. In the plasma, mefenaminic acid is chiefly bound to albumin in whose molecule there have been established two monotypic sites of binding with an association constant of approximately (1.23-1.68) . 10(5) M-1. In vivo experiments show variations in the relative indices of plasma bound mefenaminic acid as dependent on the dose and route of administration. In vitro evidence correlates with the results obtained in experiments made in vivo.