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Simple Summary: The use of veterinary drugs in fish farms is required to maintain animal health, minimize economic losses, and increase productivity. This study investigated the residue depletion profile of sulfadimethoxine (SDM) and ormetoprim (OMP) in Nile tilapia (Oreochromis sp.) after oral administration aiming to estimate a minimum withdrawal. The medicated feed used was prepared and analyzed to ensure suitability for animal treatment and prevent environmental contamination. After treatment, fish were euthanized at different times, their fillets were collected, and the drug residues were determined. Two analytical methods were developed to quantify SDM and OMP in feed and fillet samples. Meanwhile, a withdrawal period of 252 °C days was estimated. Sulfadimethoxine (SDM) and ormetoprim (OMP) are antimicrobials used in combination to treat bacterial infections in fish farming. The use of this drug combination is not yet regulated in some countries, such as Brazil. Due to the lack of regulated drugs for aquaculture in Brazil, this study investigated the residue depletion profile of SDM and OMP in Nile tilapia (Oreochromis sp.) after oral administration. Fish were treated with medicated feed containing a 5:1 ratio of SDM:OMP at the dose of 50 mg kg BW−1 for five consecutive days with an average water temperature of 28 °C. The drugs were incorporated into the feed by using a gelatin coating process which promoted homogeneity in drug concentration and prevented the drug leaching into the water during medication. The SDM and OMP determination in fish fillets (muscle plus skin in natural proportions) was performed using the QuEChERS approach followed by LC-MS/MS quantification. The analytical method was validated according to Brazilian and selected international guidelines. A withdrawal period of 9 days (or 252 °C days) was estimated for the sum of SDM and OMP residues at concentration levels below the maximum residue level of 100 µg kg−1. [ABSTRACT FROM AUTHOR]

Thiamphenicol (TAP) and florfenicol (FFC) combination has in vitro and in vivo synergistic activity against fish bacterial pathogens. However, a lack of information on its pharmacokinetics (PK) and pharmacodynamics (PD) in fish limits its further application. Therefore, this study aimed to develop and validate analytical methods for simultaneous detection and quantification of TAP and FFC in tilapia plasma and muscle plus skin samples and to determine the PK in freshwater tilapia at 30 ± 0.32 °C after a single oral dose of 5 mg kg−1 TAP +3.75 mg kg−1 FFC. Antimicrobial concentrations were analyzed by HPLC-MS. The PK characteristics were estimated by a non-compartmental model (linear up/log down). Precise, and sensitive methods were developed using ethyl acetate (plasma) and a modified QuEChERS (muscle plus skin) for extraction. Both methods were successfully applied to analyze the plasma and muscle plus skin samples in the PK study. The highest concentrations of TAP and FFC were detected at 0.5 h (6.34 and 3.34 μg mL−1) and 16 h (8.20 and 11.37 μg mL−1) post-administration in plasma and muscle, respectively. There was no significant difference between the peak concentration and apparent volume of distribution during the terminal phase of each antimicrobial in different tissues. However, the peak time, the area under the concentration-time curve, and mean residence time were higher in the muscle, for both antimicrobials (P < 0.05). The calculated PK parameters and the curve obtained for both antimicrobials emphasize their fast absorption and distribution even when used in combination. The results from this study could help establish antimicrobial susceptibility testing interpretative categories and design rational dosing regimens for TAP and FFC combination. • Plasma and muscle plus skin pharmacokinetics of TAP and FFC in tilapia after single oral administration of TAP + FFC combination were determined for the first time. • The developed and validated HPLC-MS/MS method is precise and sensitive for the simultaneous determination of TAP and FFC in fish plasma and muscle plus skin. • TAP and FFC had fast absorption and distribution in freshwater tilapia reared at 30 ± 0.32 °C. • Peak concentrations in both tissues were 2–22 times higher than the reported MIC values of the antimicrobials against several sensitive fish pathogens. [ABSTRACT FROM AUTHOR]

ABSTRACT Water temperature is a critical environmental parameter that significantly influences fish metabolism. This study assessed the metabolism of florfenicol (FF) in tilapia (Oreochromis niloticus) at water temperatures typical of tropical and subtropical regions. Fish were treated with FF by oral administration of a dose of 10 mg kg−1 bw for 10 consecutive days. Fish fillet, liver, and kidney were sampled during the treatment phase (1, 5, and 10 days) and posttreatment (1, 2, 3, and 5 days after the last FF administration). FF, florfenicol amine (FFA), monochloro florfenicol (FFCl), and florfenicol alcohol (FFOH) were determined in the sampled tissues using a validated LC–LC–MS/MS method. The highest FF, FFA, and FFOH concentrations were determined on day 5 during the treatment phase. For FF, the concentration order is kidney > liver > fillet, while for the metabolites FFOH and FFA, the order is liver > kidney > fillet. In fillet and liver, the concentrations of FFOH were higher than the FFA concentrations, indicating that FFOH was the primary metabolite in these tissues. FFCl was only quantified at concentrations lower than 90 μg kg−1 in all tissues. The results indicated that FF can be readily absorbed and rapidly eliminated in tilapia cultivated in warm water environments. This study revealed FFOH as the primary and most persistent metabolite in tilapia farmed in warm water, followed by FFA. [ABSTRACT FROM AUTHOR]

• An original bioanalytical method for erythromycin residues analysis in fish was developed, optimized, and validated. • The combination of two modern extraction techniques promoted high detectability. • The method was successfully applied in real samples to evaluate residual depletion of erythromycin in fish. An analytical method for the determination of erythromycin A (ERY) residues in fish fillet was developed, optimized, and validated employing a modified QuEChERS procedure associated to DLLME technique as a preconcentration step. The obtained LOD and the LOQ were 0.1 µg kg−1 and 1 µg kg−1, respectively. The validated method provides linearity in the range of 1 to 20 µg kg−1, precision (CV < 6.3 %) and accuracy (recovery ranging from 103 to 110 %). The procedure was applied in an experimental study to evaluate the residual depletion profile of ERY in fish (Piaractus mesopotamicus) after oral administration. The treatment was carried out at a daily dose of 100 mg (kg BW)-1 of ERY, for 7 consecutive days and with an average water temperature of 30 °C. A withdrawal time of 240°-day was estimated for eliminating ERY residues at concentration levels below the maximum residue limit considered (MRL 100 µg kg−1). [ABSTRACT FROM AUTHOR]