[Anaerobic serum ultrafiltration--a new method for determination of protein-binding rates of drugs under physiological conditions (author's transl)].

Only the free and not the protein-bound fraction of a drug shows pharmacologic activity. Therefore the rates of drug-binding to serum proteins are of great importance for clinical and pharmacological purposes. A basis prerequisite for accurate measurements are experimental designs giving the possibility of keeping the most important factors influencing the protein-binding rate within physiological ranges. In vivo these factors are, among others, the concentration of albumin, the absorption of different exogenous and endogenous substances to albumin, the type and the amount of ions present, the total ionic strength, the pH-value and hence the pCO2 as well as the temperature. An experimental set-up was described giving the possibility of keeping all these factors absolutely constant under in vivo conditions by means of a newly developed and simply to handle ultrafiltration device. From withdrawing the blood sample from the vein to the complete separation of the protein-bound fraction the blood sample can be processed under strictly anaerobic conditions (to prevent loss of CO2!). Compared to common methods generally used for the determination of protein-binding rates, such as equilibrium dialysis, column chromatography and ultracentrifugation, this new procedure saves a considerable amount of time. Within 1 h up to 8 samples can be processed in a single device. Besides short filtration times there is no need for any additional sample preparation such as buffering or adding antibacterial substances, etc.