Determination and kinetics of enrofloxacin and ciprofloxacin in Tra catfish (Pangasianodon hypophthalmus) and giant freshwater prawn (Macrobrachium rosenbergii) using a liquid chromatography/mass spectrometry method

Improved LC/MS/MS Quantification Using Dual Deuterated Isomers as the Surrogates: A Case Analysis of Enrofloxacin Residue in Aquatic Products

Extensive and high residue variations in enrofloxacin (ENR) exist in different aquatic products. A novel quantitative method for measuring ENR using high-performance liquid chromatography-tandem mass spectrometry was developed employing enrofloxacin-d₅ (ENR-d₅) and enrofloxacin-d₃ (ENR-d₃) as isotope surrogates. This reduced the deviation of detected values, which results from the overpass of the linear range and/or the large difference in the residue between the isotope standard and ENR, from the actual content. Furthermore, high residue levels of ENR can be directly diluted and re-calibrated by the corresponding curve with the addition of high levels of another internal surrogate without repeated sample preparation, avoiding the overflow of the instrument response. The validation results demonstrated that the method can simultaneously determine ENR residues from MQL (2 µg/kg) to 5000 × MQL (method quantification limit) with recoveries between 97.1 and 106%, and intra-precision of no more than 2.14%. This method realized a wide linear calibration range with dual deuterated isomers, which has not been previously reported in the literature. The developed method was successfully applied to the analysis of ENR in different aquatic products, with ENR residue levels varying from 108 to 4340 μg/kg and an interval of precision in the range of 0.175~6.72%. These results demonstrate that batch samples with a high variation in ENR residues (over the linear range with a single isotope standard) can be detected by the dual isotope surrogates method in a single sample preparation process.

Effect of food processing (fish burger preparation and frying) on residual levels of enrofloxacin and ciprofloxacin

The influence of fish burger preparation and frying on residual levels of enrofloxacin (ENR) and ciprofloxacin (CIP) was evaluated. For this purpose, a high-throughput liquid chromatography-mass spectrometry analytical method for the quantitation of ENR and CIP residues in tilapia products (fillet, raw fish burger and fried fish burger) was developed and validated based on European and Brazilian guidelines. Sample preparation was accomplished by extraction with acidified acetonitrile followed by clean-up with hexane. Chromatographic analysis was performed on a C₁₈ column using isocratic elution with 0.1% formic acid and acetonitrile (85:15 v:v). The analytical method showed suitable performance to quantify the residual levels of ENR and CIP in the studied matrices. No reduction in the residual levels of ENR and CIP was observed during fish burger preparation and only a 10% reduction occurred as a consequence of frying, indicating that both compounds were stable to the preparation of the fish burger and to frying conditions.

Pharmacokinetic/pharmacodynamic relationship of enrofloxacin against Aeromonas hydrophila in crucian carp (Carassius auratus gibelio)

The pharmacokinetic (PK) properties of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated in crucian carp following oral administration at different dose levels (5, 10, 20, 40 mg/kg body weight). The disposition kinetics of ENR was found to be linear over the dose range studied. Serum half-lives ranged from 64.56 to 72.68 hr. The in vitro and ex vivo activities of ENR in serum against a pathogenic strain of Aeromonas hydrophila were determined. In vitro and ex vivo bactericidal activity of ENR was concentration dependent. Dosing of 10 mg/kg resulted in an AUC/minimum inhibitory concentration (MIC) ratio of 368.92 hr and a C_max /MIC ratio of 7.23, respectively, against A. hydrophila 147 (MIC = 0.48 μg/ml), indicating a likely high level of effectiveness in clinical infections caused by A. hydrophila with MIC value ≤ 0.48 μg/ml. Modeling of ex vivo growth inhibition data to the sigmoid Emax equation provided the values of AUC_24 hr /MIC required to produce bacteriostasis, bactericidal activity, and elimination of bacteria, these values were 21.70, 53.01, and 125.21 hr, respectively. These findings in conjunction with MIC₉₀ data suggested that ENR at the dose of 7.81 mg/kg predicted a positive clinical outcome and minimize the risk of emergence of resistance.

Sources and fate of antimicrobials in integrated fish-pig and non-integrated tilapia farms

Antimicrobial contamination in aquaculture products constitutes a food safety hazard, but little is known about the introduction and accumulation of antimicrobials in integrated fish-pig aquaculture. This study, conducted in 2013, aimed to determine the residues of 11 types of antimicrobials by UPLC-MS/MS analysis in fish feed (n=37), pig feed (n=9), pig manure (n=9), pond sediment (n=20), fish skin (n=20) and muscle tissue (n=20) sampled from integrated tilapia-pig farms, non-integrated tilapia farms and fish feed supply shops. There was a higher occurrence of antimicrobial residues in fish skin from both integrated and non-integrated farms, and in pig manure. Enrofloxacin (3.9-129.3μg/kg) and sulfadiazine (0.7-7.8μg/kg) were commonly detected in fish skin and muscle, pig manure and pond sediment from integrated farms, with different types of antimicrobials found in pig manure and tilapia samples. In non-integrated farms, sulfadiazine (2.5-89.9μg/kg) was the predominant antimicrobial detected in fish skin and muscle, fish feed and pond sediment. In general, antimicrobials seemed not to be commonly transmitted from pig to fish in tilapia-pig integrated farms, and fish feed, pig feed and pond sediment did not seem as important sources of the antimicrobials found in fish from both systems. The frequent findings of antimicrobial residues in fish skin compared with fish muscle was probably due to different pharmacokinetics in different tissue types, which have practical food safety implications since antimicrobial residues monitoring is usually performed analyzing mixed skin and fish muscle samples.

Pharmacokinetics of enrofloxacin after oral, intramuscular and bath administration in crucian carp (Carassius auratus gibelio)

The pharmacokinetics of enrofloxacin (ENR) was studied in crucian carp (Carassius auratus gibelio) after single administration by intramuscular (IM) injection and oral gavage (PO) at a dose of 10 mg/kg body weight and by 5 mg/L bath for 5 hr at 25°C. The plasma concentrations of ENR and ciprofloxacin (CIP) were determined by HPLC. Pharmacokinetic parameters were calculated based on mean ENR or CIP concentrations using WinNonlin 6.1 software. After IM, PO and bath administration, the maximum plasma concentration (C_max ) of 2.29, 3.24 and 0.36 μg/ml was obtained at 4.08, 0.68 and 0 hr, respectively; the elimination half-life (T_1/2β ) was 80.95, 62.17 and 61.15 hr, respectively; the area under the concentration-time curve (AUC) values were 223.46, 162.72 and 14.91 μg hr/ml, respectively. CIP, an active metabolite of enrofloxacin, was detected and measured after all methods of drug administration except bath. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in the crucian carp using IM, PO and bath immersion administration.

Investigation and management of an outbreak of multispecies mycobacteriosis in Australian lungfish (Neoceratodus fosteri) including the use of triple antibiotic treatment

Disease due to non-tuberculous mycobacteria (NTM) is common in fish. Current recommendations focus on outbreak management by depopulating entire fish stocks and disinfecting tanks. Treatment is not advocated. Treatment may be appropriate, however, where individual, valuable fish are concerned. ZSL London Zoo managed an outbreak of mycobacteriosis in a valuable group of imported F1 captive-bred Australian lungfish (Neoceratodus fosteri) by depopulation, isolation, extensive testing and daily oral antibiotic treatment. Four species of Mycobacterium (M. marinum, M. fortuitum, M. chelonae and M. peregrinum) were involved in this outbreak, each with unique antibiotic sensitivities. Triple therapy with rifampicin, doxycycline and enrofloxacin for 8 months was the most effective antibiotic combination, resulting in full disease resolution. No side effects were noted and, more than 18 months post-treatment, no recurrence had occurred. This is the first report of mycobacterial disease in lungfish and the first report of a polymycobacterial outbreak in fish involving these four species of Mycobacterium. This report demonstrates the value of extensive isolation and identification. Also, as therapies currently advised in standard texts did not reflect the antibiotic sensitivity of the NTM found in the fish reported here, we recommend that antibiotic treatment should always be based on sensitivity testing.