Correlation between oral fluid and plasma oxytetracycline concentrations after intramuscular administration in pigs

The penetration of oxytetracycline (OTC) into the oral fluid and plasma of pigs and correlation between oral fluid and plasma were evaluated after a single intramuscular (i.m.) dose of 20 mg/kg body weight of long-acting formulation. The OTC was detectable both in oral fluid and plasma from 1 hr up to 21 day after drug administration. The maximum concentrations (C_max ) of drug with values of 4021 ± 836 ng/ml in oral fluid and 4447 ± 735 ng/ml in plasma were reached (T_max ) at 2 and 1 hr after drug administration respectively. The area under concentration-time curve (AUC), mean residence time (MRT) and the elimination half-life (t_1/2β ) were, respectively, 75613 ng × hr/ml, 62.8 hr and 117 hr in oral fluid and 115314 ng × hr/ml, 31.4 hr and 59.2 hr in plasma. The OTC concentrations were remained higher in plasma for 48 hr. After this time, OTC reached greater level in oral fluid. The strong correlation (r = .92) between oral fluid and plasma OTC concentrations was observed. Concentrations of OTC were within the therapeutic levels for most sensitive micro-organism in pigs (above MIC values) for 48 hr after drug administration, both in the plasma and in oral fluid.