Abstract

Enrofloxacin (EFX) is a second generation fluoroquinolone for veterinary use only. It is used in some countries as a therapeutic for diseases of productive interest. The objective of the study was to determine EFX concentrations in muscle and skin of rainbow trout, administered orally and in immersion baths at two different models and establish withdrawal period. Rainbow trout of 190 ± 25 g of weight were randomly selected, distributed in 3 batches of 45 fish each, batch A received an oral dose of 10 mg/kg, for the immersion bath, batch B was administered a dose of 20 mg/L for 2.5 hours and batch C 100 mg/L for 0.5 hours. Fishes were sacrified at different times from 0.25 to 120 hours post-application. Sample pretreatment was performed with trichloroacetic acid, mechanically homogenized and kept at rest for 12 hours, centrifuged and 150 µL of the supernatant was added with methanol, deionized water and internal standard, obtaining the solution to elute. A C-18 column, fluorescence detector and mobile phase composed of water, acetonitrile, triethylamine was used. The pharmacokinetic analysis was performed using the PKSolutions 2.0 software and withdrawal time calculation was performed by EMEA W.T 1.4 program. In all batches, tissue concentrations of EFX were detected up to 120 hrs. In batch A concentrations were ≤ 1.7 µg/g in skin and muscle, while in batch B and C the maximum concentrations for muscle and skin were 0.5 and 0.7 µg/g respectively, reached at different times, and with a elimination half-life less than batch A. Withdrawal periods were 14 and 46 days in batch A, 4 and 18 days in batch B and 5 and 11 days batch C, for muscle and skin, respectively. According to the results, immersion baths provides therapeutic concentrations, and compatible withdrawal periods with the production cycle.