PHARMACOKINETICS OF ENROFLOXACIN IN THE RED PACU (COLOSSOMA-BRACHYPOMUM) AFTER INTRAMUSCULAR, ORAL AND BATH ADMINISTRATION

The intramuscular (i.m.), oral (p.o.), and bath immersion disposition of enrofloxacin were evaluated following administration to a cultured population of red pacu. The half-life for enrofloxacin following i.m. administration was 28.9 h, considerably longer than values calculated for other animals such as dogs, birds, rabbits, and tortoises. The 4 h maximum concentration (C-max) of 1.64 mu g/mL following a single 5.0 mg/kg dosing easily exceeds the in vitro minimum inhibitory concentrat ion (MIG) for 20 bacterial organisms known to infect fish. At 48 h pos t i.m. administration, the mean plasma enrofloxacin concentration was well above the MIC for most gram-negative fish pathogens. The gavage m ethod of oral enrofloxacin administration produced a C-max of 0.94 mu g/mL at 6-8 h. This C-max was well above the reported in vitro MIC. A bath immersion concentration of 2.5 mg/L for 5 h was used in this stud y. The C-max of 0.17 mu g/mL was noted on the 2 hour post-treatment pl asma sample. Plasma concentrations of enrofloxacin exceeded published in vitro MIC's for most fish bacterial pathogens 72 h after treatment was concluded. Ciprofloxacin, an active metabolite of enrofloxacin, wa s detected and measured after all methods of drug administration. it i s possible and practical to obtain therapeutic blood concentrations of enrofloxacin in the red pacu using p.o., i.m., and bath immersion adm inistration. The i.m. route is the most predictable and results in the highest plasma concentrations of the drug.