Antibacterial dosage recommendations are poorly studied in elasmobranchs. Most dose regimens are based on extrapolation from mammals or reptiles. Ceftazidime is a third-generation cephalosporin that is active against bacteria such as Vibrio sp., Aeromonas sp., and Pseudomonas sp. that have been linked to disease in elasmobranchs.1-3 The pharmacokinetics of ceftazidime in twenty-five juvenile cownose rays (Rhinoptera bonasus) following a single intramuscular (i.m.) injection was studied. Ceftazidime (Fortaz, GlaxoSmithKline, NC, 27709, USA) was given at 20 mg/kg intramuscularly at time 0 to all rays. Blood samples were taken prior to administration of drug and at predefined intervals thereafter (24, 48, 72, 96 and 120 hours post-administration). All serum samples were assayed using a sensitive, high-performance liquid chromatography. The drug is best described by a two-compartment model with a rapid rise in drug concentration and decline followed by a slower subsequent elimination. Minimum inhibitory concentration (MIC) data for bacterial isolates from elasmobranchs are not well established. MIC values were estimated at between 4,000 to 16,000 ng/ml based on studies in other species.4-6 For MIC values of 4000 ng/ml a single dose of ceftazidime at 20 mg/kg provides adequate serum concentrations for at least 52 hours and at a MIC of 16,000 the concentration is present for 39 hours. Based on these data, a dose of 20 mg/kg every 2 days is recommended for cownose rays.
The authors want to thank Amy Parker, Jennifer Dancico, Josianne Romasco, Mike Stephan, Bob Snowden and Paul Moylette for their assistance with sample collection for this project. The authors thank the Iowa State University Racing Chemistry Laboratory staff for their assistance with sample processing.
* Presenting author
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