J. Malvisi

The disposition of enrofloxacin in seabream (Sparus aurata L.) after single intravenous injection or from medicated feed administration

Serum concentrations of enrofloxacin (EF) after intravenous (i.v.) or oral administration of single doses (2.5 and 10 mg/kg b.w., respectively) were investigated in seabream (Sparus aurata L.) kept in seawater at 25–27 °C. The tissue disposition of the drug was studied after oral administration. At prefixed time points, from 1 h to 5 days after administration, blood and edible tissues (muscle plus adherent skin) from 10 individuals in each group were collected and stored at −20 °C. Each serum and tissue sample was essayed for EF by HPLC after liquid–liquid extraction. Serum was also checked for the presence of the metabolite ciprofloxacin (CF). The quantification limits for EF were 0.010 μg/ml in serum and 0.015 μg/g in tissues. Following intravenous administration, considerably high serum concentrations of EF (range 2.605–3.810 μg/ml) were detected during the first 4 h. The concentrations decreased subsequently, indicating a first rapid distribution, followed by a slow phase of elimination. At the last time point of the experiment (120 h), there were still detectable amounts of EF in serum samples (range 0.040–0.087 μg/ml). Enrofloxacin levels of 0.335–1.138 μg/ml were reached in serum within 1 h after in feed administration. The maximum values were measured at 8 h (1.709–2.846 μg/ml), then slowly declined and were measurable (0.048–0.149 μg/ml) for up to 120 h. Compared to serum, lower concentrations of EF were determined in muscle plus skin: 0.156–0.398 μg/g after 1 h, 0.102–2.002 μg/g at 8 h and 0.015–0.031 μg/g at the last sample point. No CF was found in serum.

Tissue distribution and residue depletion of oxytetracycline in sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) after oral administration

Abstract Tissue distribution and residue depletion of oxytetracycline (OTC) following oral administration were evaluated in sea bream and sea bass under field conditions. Fish were held in floating cages placed in sea water and fed a commercial medicated diet containing 7.5 g/kg of OTC once daily for 14 days at a rate of 1.0% (75 mg a.i./kg) biomass per day. Muscle, liver, vertebrae, and skin with scales were sampled from fishes netted at different intervals during (2 nd , 4 th , 6 th ,10 th , and 14 th day) and after treatment (10 th , 20 th , 30 th , 40 th , 50 th , and 60 th day). OTC analyses were carried out by HPLC, after SPE extraction. In sea bream, a great variation in drug intake was evident from the inter-subject differences in OTC tissue concentrations. The highest recorded concentrations were in skin and pooled liver (7.70 ± 6.71 μg/g and 14.65 μg/g at the 6 th day, respectively). Vertebrae showed concentrations even six-fold higher than those in muscle, and reached steady state concentrations at the 40 th day after the end of treatment (1.73 ± 0.92 μg/g), lasting until the end of the study. OTC concentrations in muscle were lower than in all the other tissues throughout the entire experiment and declined under 0.1 μg/g 20 days after treatment ceased. In sea bass a high mortality not related to infectious diseases was observed and muscle samples had only traces or no detectable OTC levels even during medication.

Tissue distribution and depletion of flumequine after in-feed administration in sea bream (Sparus aurata)

Abstract The tissue distribution and depletion times of flumequine, a quinolone derivative, were evaluated in sea bream ( Sparus aurata ), reared under field conditions at 25–28 °C, after in-feed administration for 5 days (12 mg kg −1 body weight day −1 ). Muscle, liver, skin and vertebrae were sampled ( n = 10) at 48 h during medication and 24, 48, 96, 144, 192, 240, 288 and 480 h post-treatment. Flumequine analyses were performed by HPLC, after liquid-liquid extraction. The highest concentrations were recorded in vertebrae and skin collected 24 h after treatment (354.6 ± 132.0 ng g −1 and 317.0 ± 102.6 ng g −1 , respectively), while at the same time flumequine concentrations in muscles were 68.7 ± 49.6 ng g −1 . Flumequine disappeared from muscle 240 h after treatment ceased and showed a longer depletion rate from skin and vertebrae, which behaved as reservoir tissues.

Seabream (Sparus aurata L.): disposition of amoxicillin after single intravenous or oral administration and multiple dose depletion studies

Abstract Single dose administration (trial 1): Serum and tissue concentrations of amoxicillin (AMX) were investigated in seabream ( Sparus aurata L.) kept in seawater at 22 °C and 32‰ of salinity. Amoxicillin was given intravenously (i.v.) at 40 mg/kg b.w. or orally (p.o.) at 80 mg/kg b.w. The serum concentrations were examined by using both radioimmunoassay-microbial receptor technology (Charm II test for β-lactams) and microbiological assay (spores of Bacillus stearothermophilus ATCC 10149); the tissue levels were determined by Charm II test. A slow clearance of AMX from serum was observed after i.v. administration, the concentrations at 72 h ranging from 0.94 to 0.66 μg/ml. Despite using the trihydrate form of amoxicillin, the apparent oral bioavailability was only 0.33%. Low levels were determined in muscle, skin and liver. Multiple dose administration (trial 2): A depletion kinetic study was conducted at water temperature of 22–26 °C after in feed administration (10 days) of AMX at the dose of 80 mg/kg b.w./day. AMX was only occasionally detected at very low concentrations in muscle, liver, skin, and vertebrae both during and after treatment cessation. Different formulations (conventional, micronized and microencapsulated AMX) were assayed in seabream at 24–26 °C after a 5-day period on medicated diet at the dose of 80 mg/kg b.w./day (trial 3) to verify if the nonconventional forms could improve the tissue distribution of AMX after in-feed administration. The results achieved in muscle and adherent skin were below the LOQ at each scheduled sampling time regardless of the formulation administered.