Pharmacokinetics of oxytetracycline in the red pacu (Colossoma brachypomum) following different routes of administration

Oxytetracycline (OTC) pharmacokinetics were studied in the red pacu ( Colossoma brachypomum ) following intravenous (i.v.) and intramuscular (i.m.) administration at a dose of 5 mg/kg body weight. OTC plasma concentrations were determined by high-performance-liquid-chromatography (HPLC). A non-compartmental model was used to describe plasma drug disposition after OTC administration. Following i.m. administration, the elimination half-life ( t _½) was 62.65 ± 1.25 h and the bioavailability was 49.80 ± 0.01%. After i.v. administration the t _½ was 50.97 ± 2.99 h, the V d was 534.11 ± 38.58 mL/kg, and CI _b was 0.121 ± 0.003 mL/min.kg. The 5 mg/kg i.v. dose used in this experiment resulted in up to 48 h plasma concentrations of OTC above the reported MIC values for some strains of fish pathogens such as Aeromonas hydrophila , A. liquefaciens , A. salmonicida , Cytophaga columnaris , Edwardsiella ictaluri , Vibrio anguillarium , V. ordalii , V. salmonicida and Yeersinia ruckeri . These MIC values are below the susceptible range (4 μg/mL) listed by the National Committee for Clinical Laboratory Standards (NCCLS) as determined by the NCCLS susceptibility interpretive criteria.