Comparison of pharmacokinetic parameters for two oxytetracycline preparations in pigs.

Pharmacokinetics of oxytetracycline (OTC) were studied in 10 pigs after administration of 20 mg/kg body weight of either a conventional (OTC-C) or a long-acting (OTC-LA) preparation. After intravenous administration of OTC-C the elimination half-life for OTC was 3.75 h, with approximately 75% of the dose being excreted in the urine in 1 week. Intramuscular (i.m.) injection of OTC-C resulted in plasma peak values after 4 h, while OTC-LA after i.m. administration produced the highest plasma levels within 1 h, although these were lower than with OTC-C. For both preparations the bioavailability after i.m. administration was 95-100% and about 70% of the dose was excreted in the urine during the first week. With OTC-C given i.m., plasma concentrations above 0.5 micrograms/ml were maintained for 28 h and with OTC-LA for 35 h indicating a weak retard effect of the latter. Pronounced tissue damage at the injection site was seen 1 and 2 weeks after the administration of OTC-LA, while OTC-C produced very little irritation. OTC could be found at the injection site for 2 weeks, the concentrations being higher for OTC-LA than for OTC-C.