The interaction of albumin and drugs with two haemofiltration membranes.

The sorption of phenobarbitone sodium, barbitone sodium and fluconazole onto haemofiltration membranes made from polysulphone or a co-polymer of polyamide and polyvinylpyrrolidone was investigated in the presence and absence of albumin. The sorption of albumin was also followed in the presence of phosphate-buffered saline. Drug binding to the membrane was found to be reversible. Knowledge of the lipophilicity of the drug and hydrophobic/hydrophilic nature of the membrane did not allow successful prediction of the extent of binding of all the drugs; nor did knowledge of the extent of ionization of the drug and the charge of the membrane. Albumin bound to the polysulphone membrane in a manner that suggested the surface area to which it was binding was around 10 times greater than reported. In the presence of albumin there was a larger coefficient of variation in the binding of drugs to both membranes. The presence of albumin significantly decreased the binding of fluconazole, but not the other drugs, to the polysulphone membrane; however, albumin had no effect on the binding of any of these drugs to the polyamide membrane. We conclude that the binding of drugs to haemofiltration membranes cannot be simply predicted from knowledge of the hydrophilic/hydrophobic nature or charge of the drug and membrane, nor from the protein binding of the drug.