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

Abstract

1. The pharmacokinetics and bioavailability of oxolinic acid and oxytetracycline were studied in rainbow trout at a water temperature of 16°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 (V_darea) were 1˙94 1/kg and 1˙34 1/kg.

3. The apparent oral bioavailabiiity 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.