Therapeutic aminoglycoside antibiotic levels in brown shark, Car char hinus plumb eus (Nardo)

Abstract. The kinetics of gentamicin and tobramycin in juvenile brown sharks, Carcharhinus plumbeus (Nardo), were studied using a commercially available radioimmune assay (Clinical Assays, Cambridge, Massachusetts). Preliminary recovery studies in vitro demonstrated 95% recovery of antibiotic spiking with no detection of interfacing substances. There were no differences between serum and plasma data using this assay. Both drugs demonstrated distinct two-compartment characteristics. The mean half-life of the alpha component was 5.4±1.0 h for gentamicin and 3.2±0.5 h for tobramycin. The half-lives of the beta components were markedly longer, 54±4.9 h for gentamicin and 48±2 h for tobramycin. The experimental designs could not exclude third compartments. A therapeutic dosage schedule for gentamicin of 2 mg/kg intramuscularly followed by 1 mg/kg at 8 and 72 h was tested. This schedule avoided plasma levels greater than 12μg/ml and troughs greater than 2 μg/ml but more frequent administration may be required to treat infections with bacteria which are less sensitive to aminoglycoside antibiotics. A therapeutic tobramycin schedule of 2.5 mg/kg intramuscularly followed by 1.0 mg/kg, 4 h later and daily thereafter, achieved plasma levels within the human therapeutic range (5.8μg/ml) on the second day of therapy. Levels considered toxic to humans were not reached for 5 days.     

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.