Plasma bioavailability of 2 long-acting oxytetracycline formulations in the pig

Two commercially available long-acting oxytetracycline (OTC-LA) formulations were administered by intramuscular injection in 2 groups of 10 clinically healthy pigs at the recommended dose level of 20 mg/kg. Plasma concentrations were analysed by high-performance liquid chromatography (HPLC) of a period of 0 to 84 h. The limit of quantification of the assay was 0.125 microgram/ml. The comparison of the CMAX did not reveal any significant differences (4.45 +/- 1.30 and 4.40 +/- 0.9 micrograms/ml). The results were similar for the TMAX (3.60 +/- 1.58 and 4.00 +/- 2.67 h). The areas under the curve were also similar. The AUC0-84 h results were respectively 92.8 +/- 14.1 and 96.3 +/- 11.3 mg.h/l and the AUC0-infinity results were 99.5 +/- 14.7 and 106.7 +/- 15.4 mg.h/l. No significant difference was found. This may be considered as a preliminary study to demonstrate the bioequivalence of the 2 preparations. On the basis of the statistical analysis of the results obtained, a cross-over study using 2 groups of 20 animals is theoretically necessary for such a demonstration.