[Serum protein binding of T-3761]

We investigated the extent of the binding of T-3761 to serum protein and obtained the following results. 1. The binding rates of T-3761 to serum protein from various animals and human were 16.9-27.7%, and a little higher than those of ciprofloxacin and ofloxacin. 2. The binding rates of T-3761 to human serum protein were 19.1-23.8% at concentrations of 0.25-20 micrograms/ml. 3. The binding rates of T-3761 lowered as the decrease of protein concentration. 4. The binding rates of T-3761 (2 micrograms/ml) to human serum protein were 12.4, 21.3 and 32.1% at pH 7.0, 7.4 and 8.0, respectively, showing the effect of the pH. 5. The binding of T-3761 to human serum protein was reversible. 6. In vivo binding rates of T-3761 in rabbits after a single oral administration of 20 mg/kg were 26.1-33.2%, which were similar to those obtained in vitro.