Comparative pharmacokinetics and bioavailability of oxolinic acid and oxytetracycline in rainbow trout (Oncorhynchus mykiss).

1. The pharmacokinetics and bioavailability of oxolinic acid and oxytetracycline were studied in rainbow trout at a water temperature of 16 degrees C after intravascular (10 and 20 mg/kg, respectively) and oral (75 mg/kg) dosing. 2. The pharmacokinetics were best described by a two-compartment open model giving distribution half-lives of 0.31 h and 1.53 h, and elimination half-lives of 69.7 h and 60.3 h for oxolinic acid and oxytetracycline, respectively. The respective volumes of distribution (Vdarea) were 1.94 l/kg and 1.34 l/kg. 3. The apparent oral bioavailability for oxolinic acid and oxytetracycline was 13.6% and 5.6%. 4. The plasma protein binding was 27% for oxolinic acid and 55% for oxytetracycline. 5. Both drugs were well tolerated, the acute oral toxicities (LD50) exceeding 4000 mg/kg.