Effects of a perfluorochemical blood substitute on diazepam binding by human albumin

The binding of 0.4 microgram mL-1 diazepam and 0.75 mol diazepam mol-1 of albumin by a perfluorochemical (PFC) emulsion, Fluosol-DA, 20%, by human serum albumin (HSA), and by their mixtures, has been examined at ambient temperature. The concentration of free diazepam was determined by standard centrifugation followed by supernatant ultrafiltration. Non-specific loss of diazepam occurred to the ultrafiltration device. This loss was independent of drug concentration and a correction factor was employed to calculate the true free diazepam concentration. Diazepam was extensively bound by the PFC emulsion. The percent free diazepam increased as the emulsion concentration decreased, while the binding of diazepam appeared to be independent of drug concentration. Diazepam did not partition into the pure PFC liquids, indicating that emulsion-bound diazepam is only associated with the emulsifiers of the droplets. Diazepam was extensively bound by HSA and the percent free diazepam increased as drug concentration increased or as HSA concentration decreased. The PFC emulsion significantly displaced HSA bound diazepam in all mixtures examined. Studies with the individual and combined components of the emulsion indicated that this displacement is largely attributed to the oleic acid component and, to a much smaller degree, the Pluronic F-68 component of the emulsion.