Comparative single-dose pharmacokinetics of four quinolones, oxolinic acid, flumequine, sarafloxacin, and enrofloxacin, in Atlantic salmon (Salmo salar) held in seawater at 10 degrees C

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Abstract
Quinolones are currently the most commonly used group of antimicrobial agents in Norwegian aquaculture. The aims of this study were to examine and compare the pharmacokinetic properties of the quinolones oxolinic acid, flumequine, sarafloxacin, and enrofloxacin after intravascular and oral administration to Atlantic salmon (Salmo salar) by using identical experimental designs. The study was performed in seawater at 10.2 +/- 0.2 degree C with Atlantic salmon weighing 240 +/- 50 g (mean +/- standard deviation). The bioavailability varied considerably among the four quinolones. Following oral administration of medicated feed, the bioavailabilities of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 30.1, 44.7, 2.2, and 55.5%, respectively. Taking the different dosages (25 mg/kg of body weight for oxolinic acid and flumequine and 10 mg/kg for sarafloxacin and enrofloxacin) into account, enrofloxacin showed the highest maximum concentration in plasma, followed by flumequine, oxolinic acid, and sarafloxacin. Following intravenous administration, the volumes of distribution at steady state of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 5.4, 3.5, 2.3, and 6.1 liters/kg, respectively. Hence, all the quinolones showed good tissue penetration in Atlantic salmon. The elimination half-life of three of the quinolones, oxolinic acid, flumequine, and sarafloxacin, was less than or equal to 24 h, with oxolinic acid showing the shortest (18.2 h). On the other hand, the elimination half-life of enrofloxacin was estimated to be 34.2 h, almost twice that of oxolinic acid. This study showed that flumequine and enrofloxacin had better pharmacokinetic properties, compared with those of oxolinic acid, in Atlantic salmon held in seawater.