Plasma concentrations of oxytetracycline in swine after administration of the drug intramuscularly and orally in feed.

Four pigs were used in a 2 X 2 crossover study to determine plasma oxytetracycline (OTC) concentration and OTC pharmacokinetic variables after IM administration of 2 OTC preparations--long acting OTC and a 100-mg of OTC/ml solution (OTC-LA and OTC-100, respectively)--at a dosage of 20 mg/kg of body weight. In a second study, 3 additional pigs were given ad libitum access to feed containing pure OTC (0.55 g/kg of feed). The mean (+/- SD) peak plasma OTC concentration after OTC-LA administration was 6.0 +/- 2.2 micrograms/ml at 30 minutes; the mean peak plasma OTC concentration after OTC-100 administration was 6.7 +/- 3.4 micrograms/ml at 90 minutes. Mean plasma OTC concentration after oral OTC administration in feed peaked at 0.4 micrograms/ml 48 hours after access to OTC-medicated feed and decreased to 0.25 micrograms/ml by the end of that study. Mean plasma OTC concentration was maintained at greater than 0.5 micrograms/ml for less than 48 hours after OTC-LA administration and for less than 36 hours after OTC-100 administration. Mean plasma OTC concentration decreased to less than 0.2 micrograms/ml by 72 hours after IM administration of either product. Calculation of area under the plasma OTC concentration-time curve (AUC) did not reveal significant difference between the 2 OTC formulations. There also was not significant difference (between OTC-LA and OTC-100) in the value of the disappearance rate constant after administration of either OTC formulation. The data did not indicate significant pharmacologic advantage of OTC-LA, compared with OTC-100, when either formulation was administered IM at a dosage of 20 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)