Disposition and bioavailability of 3H-tetracycline in the channel catfish (Ictalurus punctatus)

1. The tissue disposition and bioavailability of 3H-tetracycline were examined in the channel catfish (Ictalurus punctatus) after intravascular (4 mg/kg body weight) and per os (4 and 80 mg/kg) dosing. 2. The pharmacokinetics of the intravascularly administered drug using a two-compartment open model revealed plasma half-lives of 1.3 and 16.5 h for the distribution and elimination phases, respectively. 3. The drug was highly concentrated in both hepatobiliary and urinary compartments. The concentrations in the edible flesh were the lowest of any compartment examined. 4. The apparent bioavailability of the per os-administered drug was less than 5% and was influenced by the presence of feed material and the dosage. 5. The drug was 72% bound to plasma protein at both 4 and 24 h after intravascular administration.