Pharmacokinetics and tissue disposition of enrofloxacin in rainbow trout after different routes of administration

Plasma pharmacokinetics (PK) and tissue disposition of enrofloxacin (EFX) was studied in rainbow trout (Oncorhynchus mykiss) after a single oral administration of 10 mg/kg, and by immersion baths of 20 ppm during 2.5 h and 100 ppm during 0.5 h, at water temperature of 16.3 +/- 0.3 degrees C. Concentrations of EFX in plasma and tissues (skin, muscle, liver, kidney and gut) were determined using high performance liquid chromatography (HPLC) with fluorescence detection. Pharmacokinetic parameters were analyzed with a non-compartmental model. After oral administration, t1/2 beta, AUC and AUC(tissues)/AUC(plasma) ratio were 42.98 h, 21.80 mu g-h/ml and <= 18.63, respectively. After immersion baths of 20 ppm during 2.5 h and 100 ppm during 0.5 h, the t1/2 beta, AUC and AUC(tissues)/AUC(plasma) were 42.77 and 44.67, 9.83 and 12.83 mu g-h/ml and <= 9.81 and <= 7.13, respectively. Therefore, oral (10 mg/kg) and bath administration in rainbow trout can provide AUC/MIC of >= 125 and Cmax/MIC of >= 10 to treat diseases caused by susceptible bacteria with MIC <= 0.04 mu g/ml. This information can be helpful for the right use of EFX in rainbow trout. Also, this is the first study that determines the antibiotic tissue disposition in rainbow trout by using different administration routes.