Some pharmacokinetic parameters and dosage regimens for a long-acting formulation of oxytetracycline in 6- to 8-month-old male calves.

A two-way crossover study was conducted in crossbred male calves (6-8 months old) to determine the bioavailability, pharmacokinetics and dosage regimens for a long-acting formulation of oxytetracycline (OTC-LA). The half-lives of oxytetracycline after intravenous and intramuscular administration were 7.8 h and 24 h, respectively. The volume of distribution and total body clearance values of the drug were 0.86+/-0.07 L and 76.1+/-3.3 (ml/h)/kg, respectively. The maximum concentration of the drug in the serum (4.7-7.4 microg/ml) was achieved 8-10 h after intramuscular administration. The minimum therapeutic serum concentration of drug of > or = 0.5 microg/ml was maintained between 15 min and 84 h after intramuscular administration. The intramuscular bioavailability of the drug was 89.1+/-4.2%. The dosage regimens to maintain the minimum therapeutic serum concentrations of OTC following intramuscular administration of OTC-LA were computed.