Gram-negative organisms are implicated in serious infectious diseases of reptile species, which play an important role as causes of disease and death in captive snakes. Enrofloxacin represents a good alternative to treat these bacterial infections. In previous studies, significant pharmacokinetic differences with clinical implications have been observed in the only two species of snakes studied. The pharmacokinetic behavior of enrofloxacin was assessed in six South American rattlesnakes (Crotalus durissus terrificus), following intramuscular injections of 10mg/kg. High-performance liquid chromatography was used to measure the plasma concentrations of enrofloxacin and its active metabolite, ciprofloxacin. In rattlesnakes, enrofloxacin presented a slow absorption (Tmax=7.61±3.92h) with peak plasma concentration of 5.49±2.42µg/mL and a long elimination half-life (T_1/2l=20.20±4.40h). Ciprofloxacin showed a high peak plasma concentration of 1.57±0.72µg/mL at 33.63h and the fraction of enrofloxacin metabolized to ciprofloxacin was around 45%. The long persistence (MRTt=57.71±15.78h; T_1/2l= 33.86±11.97 h) and the high values of Cmax and AUC observed for ciprofloxacin in the Crotalus genus could indicate that the active metabolite might possess a high influence in the antimicrobial effect in this species. We consider the administration of 10mg/kg of enrofloxacin by the IM route to be a good choice in rattlesnakes against infections caused by microorganisms with MIC values £2.31μg/ml.

Key words: Ciprofloxacin, Crotalus durissus terrificus, Enrofloxacin, Intramuscular, Pharmacokinetic, Rattlesnake