Evaluation of methods to determine protein-binding of drugs. Equilibrium dialysis, ultrafiltration, ultracentrifugation, gel filtration.

The reliability of the most important methods to determine protein-binding of drugs was compared. Applying these methods to different drugs solved in bovine plasma or in protein-free solutions the incidence of errors specific for each method was examined. Certain limits are found for the applicability of each method. If these limitations are observed reproducibility differs only slightly within the four methods. Considering all the results, however, the values achieved by equilibrium dialysis appear to come closest to the real extent of binding.