Marker Residue Research Articles

The effect of breed on ivermectin residues in the edible tissues of cattle and the estimated withdrawal period

This study analyzed the residue depletion kinetics of ivermectin (IVM) in Nelore and crossbred (Nelore x Angus) cattle aiming to compare the profiles between the breeds and evaluate the residue levels at the injection site. IVM 1%, at a dose of 0.2 mg/kg, was administered via the subcutaneous route, and tissue samples were collected on different days post administration for analysis by LC–MS/MS. The results revealed that the detection of the marker residue in conventional matrices such as the liver, perirenal fat, and trapezius muscle (injection site) had relatively high residue concentrations. The maximum residue limit (MRL) was exceeded at the injection site at 21- and 35-days post administration in crossbred and Nelore animals, respectively, with significant variations between animals. This study highlighted significant challenges in accurately determining the pharmacokinetic profile and withdrawal periods of IVM in cattle due to high variability in tissue residue data, particularly at injection sites. The comparison of IVM concentrations between cattle breeds was hindered by high standard errors, emphasizing the need for more rigorous sampling protocols. The results suggest that current guidelines may not adequately account for the erratic depletion kinetics of injectable formulations like IVM, especially at injection sites. Therefore, improving sampling techniques and revising guidelines are essential for accurate residue monitoring and withdrawal period determination.

Residue Depletion of Nitrofurazone Metabolites, Semicarbazide and 5-Nitro-2-Furaldehyde, in Broiler Chickens After Oral Administration.

Nitrofurazone (NFZ) antibiotic is banned in food-producing animals, and its metabolite, semicarbazide (SEM), is used as a marker residue for nitrofurazone abuse. However, SEM can also be generated during food processing without veterinary treatment. Therefore, SEM cannot be considered an unequivocal marker of NFZ. This study investigates the use of 5-nitro-2-furaldehyde (5-NF) as an additional marker for nitrofurazone in broiler chickens. After oral administration of NFZ and 5-NF at 25 mg·kg-1 BW for 10 days, tissues (muscle and liver) and plasma samples were analyzed by liquid chromatography-tandem mass spectrometry. In NFZ-treated chickens, 5-NF was detected within 1 h in plasma at a peak concentration of 1.4 ± 0.25 μg·kg-1, while in 5-NF-treated ones, the maximum concentration was 0.85 ± 0.06 μg·kg-1 after 2 h. 5-NF was not detected in muscle and liver for both treated groups from 0 to 21 days. However, SEM persisted for up to 3 weeks in muscle (0.3 ± 0.018 μg·kg-1), 2 weeks in liver (0.16 ± 0.008 μg·kg-1), and 1 week in plasma (0.4 ± 0.05 μg·kg-1) with a faster elimination rate in liver tissues (half-life of 4.6 days) compared to muscle tissues (half-life of 6.5 days). These findings suggest that SEM remains a better marker for detecting nitrofurazone abuse in chickens compared to 5-NF.

Estimation of withdrawal interval recommendations following administration of fenbendazole medicated feed to ring-necked pheasants (Phasianus colchicus).

Prescribing fenbendazole medicated feed for pheasants in the USA is considered extra-label drug use under CPG Sec 615.115, and a safe estimated withdrawal interval (WDI) must be applied following administration to this minor food-producing species. This study sought to determine the pharmacokinetic and residue depletion profile for fenbendazole and its major metabolites to estimate a WDI for pheasants following fenbendazole administration as an oral medicated feed. Pheasants (n = 32) were administered fenbendazole as an oral medicated feed (100 ppm) for 7 days. Fenbendazole, fenbendazole sulfoxide, and fenbendazole sulfone (FBZ-SO2) in liver and muscle samples were analyzed using HPLC-UV. Tissue WDIs were estimated using FDA, European Medicines Agency (EMA), and half-life multiplication methods for US poultry tolerances, EMA maximum residue limits, and the analytical limit of detection (LOD; 0.004 ppm). Terminal tissue elimination half-lives (T1/2) were estimated by non-compartmental analysis using a naïve pooled data approach. The tissue T1/2 was 14.4 h for liver, 13.2 h for thigh muscle, and 14.1 h for pectoral muscle. The maximum estimated withdrawal interval was 153 h (7 days) for FBZ-SO2 in pectoral muscle using the FDA tolerance method (95% confidence interval for the 99th percentile of the population), and the LOD as the residue limit. The results from this study support the use of FBZ-SO2 as the marker residue in the liver of pheasants and the provision of evidence based WDIs following the extra-label administration of fenbendazole medicated feed (100 ppm) for 7 days.

Safety and efficacy of a feed additive consisting of salinomycin sodium (Sacox®) for rabbits for fattening (Huvepharma N.V.).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of the coccidiostat salinomycin sodium (Sacox®) for rabbits for fattening. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concluded that the use of salinomycin sodium (SAL-Na) from Sacox® does not raise safety concerns for the target species, consumers, users and the environment with regard to the production strain. In the absence of adequate tolerance studies, the FEEDAP Panel could not conclude on the safety of SAL-Na from Sacox® for rabbits for fattening. The FEEDAP Panel concluded that the additive is safe for the consumer when it is used at the proposed maximum level of 25 mg SAL-Na/kg complete feed for rabbits and a withdrawal period of 1 day is respected. The following maximum residue limits (MRL) are proposed for the marker residue compound salinomycin (SAL): 0.2 and 0.03 mg SAL/kg for liver and kidney, respectively. The additive is not irritant to skin and eyes but should be considered a potential dermal and respiratory sensitiser. A risk for inhalation toxicity could not be excluded. The use of the SAL-Na from Sacox® in feed for rabbits for fattening up to the highest proposed level will not pose a risk for the terrestrial and aquatic compartment and ground water. The risk of secondary poisoning can be excluded for worm-eating birds and mammals, while it cannot be excluded for fish-eating birds and mammals. The FEEDAP Panel concludes that SAL-Na from Sacox® at the minimum concentration of 20 mg SAL-Na/kg complete feed has the potential to control coccidiosis in rabbits for fattening. Development of resistance to SAL-Na of field Eimeria spp. strains isolated from rabbits for fattening should be monitored.

Concurrent use of two dual-combination drenches containing monepantel/abamectin and oxfendazole/levamisole in sheep: effect on marker residues 21 and 28 days after administration

ABSTRACT Aims To determine the concentration, in comparison with the maximum residue limit (MRL), of anthelmintic marker residues in the target tissues (liver and fat) of sheep treated concurrently with two oral drenches, one containing monepantel and abamectin and the other oxfendazole and levamisole. Methods On day 0 of the study, 12 sheep (six male and six female; 8–9-months old) were dosed according to individual body weight determined the day prior. Zolvix Plus (dual-active oral drench containing 25 g/L monepantel and 2 g/L abamectin) was administered to all animals prior to administration of Scanda (dual-active oral drench containing 80 g/L levamisole hydrochloride and 45.3 g/L oxfendazole). Six sheep (three male and three female) were slaughtered 21 and 28 days after treatment and renal fat and liver samples were collected. Using validated methods, analyses for monepantel sulfone, abamectin, levamisole and oxfendazole (expressed as total fenbendazole sulfone following conversion of the combined concentrations of oxfendazole, fenbendazole and fenbendazole sulfone) were performed on liver samples while renal fat specimens were analysed for monepantel sulfone and abamectin residues only. Detected concentrations were compared to the established MRL in sheep for each analyte determined by the Ministry for Primary Industries. Results All residues detected in samples of liver and fat collected 21 and 28 days after treatment were below the MRL for each analyte. All liver samples collected on day 21 had detectable monepantel sulfone (mean 232 (min 110, max 388) μg/kg) and oxfendazole (mean 98.7 (min 51.3, max 165) μg/kg) residues below the MRL (5,000 and 500 μg/kg, respectively). Monepantel sulfone (mean 644 (min 242, max 1,119) μg/kg; MRL 7,000 μg/kg) residues were detected in 6/6 renal fat samples. Levamisole residues were detected in 3/6 livers (mean 40.0 (min 14.3, max 78.3) μg/kg; MRL 100 μg/kg), and abamectin residues in 1/6 livers (0.795 μg/kg; MRL 25 μg/kg) and 2/6 fat samples, (mean 0.987 (min 0.514, max 1.46) μg/kg; MRL 50 μg/kg) 21 days after treatment. Conclusion and clinical relevance These results suggest that concurrent administration of Zolvix Plus and Scanda to sheep is unlikely to result in an extended residue profile for any of the active ingredients, with all analytes measured being under the approved New Zealand MRL 21 days after treatment. This work was not completed in line with guidance for establishing official residue profiles, nor is it sufficient to propose a new withholding period.

Depletion kinetics of semicarbazide in giant river prawn (Macrobrachium rosenbergii) following nitrofurazone oral administration and its occurrence in an aquaculture farm

Semicarbazide (SEM), a marker residue used to monitor the use of prohibited drug nitrofurazone (NFZ), is commonly found in wild crustaceans, implying the natural origin. However, the difference between endogenous and exogenous SEM has rarely been investigated. So, tissue-bound SEM was determined in samples collected from giant river prawns cultured in an aquaculture farm and in samples from an experiment where giant river prawns were fed twice a day with NFZ at 30 mg/kg for 5 days. At day 10 of drug withdrawal, muscle SEM of the NFZ-fed prawn was 17.78 ng/g and depleted to 1.18 ng/g at day 90 (half-life 20.31 days) which was significantly higher than the control prawn (usually ≤ 0.1 ng/g). In contrast, the average SEM in the shell was independent of NFZ treatment. SEM was not found in the aquaculture farm samples, implying that the SEM in cultured prawn did not originate from SEM contamination.

Determination of marker residues of quinoxaline-1,4-di-N-oxides and its prototype identification by liquid chromatography tandem mass spectrometry

Quinoxaline-1,4-di-N-oxides (QdNOs), such as carbadox, olaquindox, mequindox, quinocetone, etc. are a class of antibacterial drugs. Prototype drugs residues can not be detected due to their rapid metabolism in animals. Quinoxaline-2-carboxylic acid (QCA) and 3-methyl-QCA (MQCA) are their common marker residues, so it has been always a challenge to trace the specific QdNOs drug used in food animal production. Herein, a liquid chromatography tandem mass spectrometry method was developed to determine QCA and MQCA, and meanwhile, the prototype drugs were identified by analyzing bis-desoxy QdNOs metabolites in single ion-pair monitoring mode. The method indicated that the average recoveries for QCA and MQCA were from 90 % to 105 % with relative standard deviations below 10 %, and the limits of quantification were 1.0 μg/kg. The limits of detection of five bis-desoxy QdNOs (qualitative markers) reached 0.5 μg/kg. This new analytical strategy can effectively solve the identification problem of QdNOs drugs in animal-derived food.

Safety and efficacy of a feed additive consisting of phenylcapsaicin (aXiphen) for chickens for fattening (aXichem AB).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of phenylcapsaicin (aXiphen®) as a zootechnical additive (functional group: physiological condition stabilisers) in feed for chickens for fattening. The additive under assessment, phenylcapsaicin, is safe for chickens for fattening up to the maximum proposed use level of 15 mg/kg complete feed. A margin of safety could not be established. Phenylcapsaicin is not genotoxic. The reference point for phenylcapsaicin derived from a 90-day repeated dose oral toxicity study in rats is 37.2 mg/kg body weight (bw) per day, the lowest of the model averaged BMDL20 values for alanine aminotransferase increase in plasma. The metabolic similarity in the laboratory animals and the target species was not demonstrated and the identity of the marker residue could not be established. In the absence of such data, the safety for the consumers could not be evaluated. The inhalation exposure of phenylcapsaicin (as liquid) for the user was considered unlikely. The FEEDAP Panel considered the additive irritant to the eyes but not to the skin and it is not a dermal sensitiser. In the absence of appropriate data, the environmental risk assessment for phenylcapsaicin could not be performed. It is unlikely that phenylcapsaicin bioaccumulates in the environment and the risk of secondary poisoning is considered low. The FEEDAP Panel could not conclude on the efficacy of the additive in chickens for fattening at the proposed conditions of use.

The presence of semicarbazide in crustaceans collected from natural habitats in Thailand

Semicarbazide (SEM) has been used as a marker residue of the banned veterinary drug nitrofurazone (NFZ). Although evidence indicates that SEM can be found in some natural crustaceans that have never been exposed to NFZ, such information is limited to a few species. The present study aimed to investigate the natural occurrence of SEM in wild crustaceans in Thailand. A total of 14 species, all economically important food animals, were captured from different regions of Thailand. Tissue-bound SEM and its parent drug NFZ were determined by the UPLC-MS/MS and LC-MS methods, respectively. The results showed that while NFZ was not detected in any samples, the tissue-bound SEM could be found in every natural crustacean species investigated. However, the prevalence and concentration varied greatly. The occurrence of SEM in the freshwater palaemonid Macrobrachium prawns is generally much higher than in the marine penaeid shrimps/prawns. SEM was found in 33% and 80% of the giant river prawn (Macrobrachium rosenbergii) muscles (<0.10–0.46 ng/g) and shells (3.68–13.22 ng/g), respectively. In contrast, SEM was not detected in the muscles of penaeid shrimps/prawns (with few exceptions), but it was occasionally found in the shells at low levels (usually <1 ng/g). The shells of saltwater crabs also contained higher levels of SEM than the muscles. For instance, the highest SEM levels detected in the mud crab (Scylla sp.) muscles and shells were 0.40 and 22.75 ng/g, respectively. However, the situation was reversed for the rice-field crab (Sayamia sp. and Esanthelphusa sp.), in which SEM was not detected in all shells but detected in the muscles (up to 1.46 ng/g). The fact that SEM is often found in wild crustaceans implies a natural origin of this substance. Consequently, using SEM as a marker residue of NFZ is controversial and should be reconsidered.

Exposure Assessment of Nitrofuran Metabolites in Fish and Honey Produced in Armenia: A Pilot Investigation.

In Armenia, the presence of nitrofuran residues in food products is unacceptable for both domestic sales and export. However, food may contain nitrofuran metabolites (NMs) due to the illegal use of these drugs in the agrofarming practice. This study aimed to identify NMs as the marker residues for nitrofurans in fish and honey produced in Armenia and assess the potential health risks associated with consuming these foods. The commodities studied were natural honey and three species of farmed fish produced by various regions nationwide. Concentrations of the marker metabolites (3-amino-2-oxazolidinone (AOZ), 3-amino-5-methylmorpholino-2-oxazolidinone (AMOZ), 1-aminohydantoin (AHD), and semicarbazide (SEM)) were determined through an enzyme-linked immunosorbent assay (ELISA) and verified using liquid chromatography-mass spectrometry (LC-MS/MS). Consumer groups were identified based on their average daily intake of foods. Health risk was assessed by calculating the margin of exposure (MOE). Reference values for health risk assessment were obtained from the European Food Safety Authority (EFSA). Results showed that 33.3% of fish samples and 44.4% of honey samples contained NMs, the mean concentrations ranging from 0.05 μg/kg to 0.52 μg/kg. All MOE values obtained were over 10,000, indicating that the detected concentrations of NMs in fish and honey produced in Armenia pose no health risk to consumers. However, these results highlight the illicit use of highly toxic substances and the need for improved control of farming practices.

A Comparable icELISA and Lateral Flow Immunoassay for the Sensitive and Rapid Detection of 4,4'-Dinitrocarbanilide in Chicken.

4,4'-dinitrocarbanilide (DNC) is a key component and marker residue of nicarbazin, which forms residues in edible tissue and then causes nephrotoxicity and hepatotoxicity in humans if used excessively. To simplify sample preparation and monitor the DNC rapidly and accurately, a comparable icELISA and lateral flow immunoassay (LFIA) was developed in this study. Briefly, the reaction parameters were explored for improving the sensitivity of icELISA and LFIA. Under the optimal conditions, methanol was selected as the extracting solvent for DNC in chicken, and 20- and 10-fold dilutions of sample extraction eliminated the matrix effect for icELISA and LFIA, separately. After sample pretreatment, the analysis properties of icELISA and LFIA were compared. The limit of detection of icELISA for DNC was 0.8 μg/kg, and the visual and quantitative limits of detection of LFIA were 8 and 2.5 μg/kg. Compared with icELISA, LFIA showed lower sensitivity but obvious advantages in terms of matrix tolerance and detection time (within 15 min). The sensitivity, specificity, and accuracy of the developed assays satisfied the detection requirement even if using simple sample pretreatment. This comparable icELISA and LFIA provided mutual verifiability methods for the accurate detection of DNC in chicken.

Residue depletion of toltrazuril and its metabolites in egg after an authorised application in hens

Toltrazuril is effective against all coccidial parasites in most animal species. Pharmacological studies showed that toltrazuril was well absorbed in the gastrointestinal tract and rapidly metabolised to toltrazuril sulfoxide and toltrazuril sulfone (ponazuril), the latter being considered as marker residue for toltrazuril residues. The maximum residue limits (MRLs) for toltrazuril sulfone in edible tissues from poultry range from 100 μg/kg in muscle to 600 μg/kg in liver. The substance is currently not allowed for use in poultry producing eggs for human consumption. However, several veterinary medicinal products containing the active substance are authorised in the European Union for use in pullets. According to product literature, withdrawal periods for edible tissues from chickens of 12 up to 18 days as well as restrictions for use before the onset of laying must be observed. Depending on the chicken breed, the start of the laying activity can vary between the 17th and 20th week of age. In monitoring programs, certain cases of residues in eggs were detected although zero tolerance was applicable at that time. The objective of the presented study was to evaluate the residue depletion profiles of toltrazuril and its major metabolites after the treatment of 15-week-old laying hens with an authorised toltrazuril-containing veterinary medicinal product. The pullets were treated on two consecutive days with TOLTRA-K (25 mg/ml) oral solution via drinking water at a dosage of 7 mg of toltrazuril per kg of body weight per day according to the recommended posology. Individual egg samples were collected after the beginning of the laying activity and were analysed in duplicate by LC-MS/MS to determine residues of toltrazuril and its metabolites. Residues of toltrazuril sulfone in egg samples were detected for several weeks and a statistical model was established to determine the time span needed to meet the zero tolerance.

Analysis of Transfer of Tiamulin to Animal Tissue after Oral Administration: An Important Factor for Ensuring Food Safety and Environmental Protection.

The administration of veterinary medicinal products containing tiamulin hydrogen fumarate (THF) leads to the appearance of the following residues in animal tissues: THF and metabolites that can be hydrolyzed to 8-α-hydroxymutilin. The marker residue for tiamulin, according to Regulation EEC 2377/90, is the sum of the metabolites that can be hydrolyzed to 8-α-hydroxymutilin. The main aim of this study was to analyze the depletion of tiamulin residues and metabolites that can be hydrolyzed to 8-α-hydroxymulinin by liquid chromatography with tandem mass spectrometry (LC-MS/MS) in pig, rabbit and bird tissues after tiamulin administration and to determine minimum withdrawal times for products of animal origin intended for human consumption. Tiamulin was administered orally as follows: 12,000 µg/kg body weight/day for 7 days to pigs and rabbits and 20,000 µg tiamulin/kg body weight/day for 7 days to broiler chickens and turkeys. The values found for tiamulin marker residues were 3 times higher in liver than in muscle in pigs, 6 times in rabbits and 8-10 times in birds. The content of tiamulin residues in eggs from laying hens was below 1000 µg/kg at all times of analysis. The minimum withdrawal times for animal products intended for human consumption, resulting from this study, are 5 days for pigs, rabbits and turkeys, 3 days for broiler chickens and 0 days for eggs.

Using simulations to explore the potential effect of disease and inflammation on the frequency of violative flunixin residues in cattle.

The US Food and Drug Administration (FDA) assigns a tolerance and withdrawal period when evaluating new drugs for use in food-producing species. Because withdrawal periods are determined from data generated in normal, healthy animals, questions have been raised regarding whether disease and inflammation can be a factor associated with some residue violations. We explored this question using flunixin liver concentrations as a model situation. Using data contained in the flunixin FOI Summary (NADA 101-479) and Monte Carlo simulation, we generated sets of residue depletion data. Our mathematical model was simple linear regression containing the terms alpha (the marker residue back-extrapolated to time zero, which equals ) and beta (the elimination rate constant which equals ). By modifying alpha and beta means and variances, we determined the smallest change in these parameters that would result in the presence of violative residues above the statistically determined expected frequency of 1%. The results of this in silico study indicated that the magnitude of change in alpha and beta needed to generate violative residues exceeds that likely to occur due to disease or inflammation when flunixin is used in accordance with the approved product label.

Metabolic Disposition and Elimination of Tritum-Labeled Sulfamethoxazole in Pigs, Chickens and Rats.

Sulfamethoxazole (SMZ), as a sulfa antibiotic, is often used in the treatment of various infectious diseases in animal husbandry. At present, SMZ still has many unresolved problems in the material balance, metabolic pathways, and residual target tissues in food animals. Therefore, in order to solve these problems, the metabolism, distribution, and elimination of SMZ is investigated in pigs, chickens, and rats by radioactive tracing methods, and the residue marker and target tissue of SMZ in food animals were determined, providing a reliable basis for food safety. After a single administration of [3H]-SMZ (rats and pigs by intramuscular injection and chickens by oral gavage), the total radioactivity was rapidly excreted, with more than 93% of the dose excreted within 14 days in the three species. Pigs and rats had more than 75% of the administered volume recovered by urine. After 7 days of continuous administration, within the first 6 h, radioactivity was found in almost all tissues. The highest radioactivity and longest persistence in pigs was in the liver, while in chickens it was in the liver and kidneys, most of which was removed within 14 days. A total of six, three and three metabolites were found in chickens, rats and pigs, respectively. N4-acetyl-sulfamethoxazole (S1) was the main metabolite of SMZ in rats, pigs and chickens. The radioactive substance with the longest elimination half-life is sulfamethoxazole (S0), so S0 was suggested to be the marker residue in pigs and chickens.

Effects of temperature on the pharmacokinetics, optimal dosage, tissue residue, and withdrawal time of florfenicol in asian seabass (lates calcarifer)

Drug behavior in the bodies of fish is largely influenced by the water temperature. Antimicrobial drugs are needed for the control of bacterial outbreaks in farmed fish including Asian seabass (Lates calcarifer). However, little is known about the temperature effect on appropriate drug uses in this species. The purpose of this study was to investigate the differences in pharmacokinetics (PK), optimal dosages, tissue depletion, and withdrawal time (WDT) of florfenicol (FF) in Asian seabass reared at 25 and 30 °C. In the PK study, the fish were administered with a single oral dose of 10 mg/kg FF. The optimal dosing regimen was determined by the pharmacokinetic-pharmacodynamic (PK-PD) approach. In the tissue depletion and WDT study, FF was administered at the optimal dosages once daily for 5 days and the WDT was determined by linear regression analysis based on the sum of FF and its metabolite florfenicol amine (FFA) in the muscle/skin. When the temperature was increased from 25 to 30 °C, the elimination half-life of FF was significantly decreased from 11.0 to 7.2 h. While the other PK parameters were not changed significantly, the calculated optimal dosages for the target minimum inhibitory concentration (MIC) of 2 µg/mL were 10.9 and 22.0 mg/kg/day, respectively for 25 and 30 °C. The sum of FF + FFA is a preferable marker residue for WDT determination because differential FF metabolism was observed at different temperatures. The depletion half-life of the muscle/skin was shortened from 41.1 to 32.4 h by the 5 °C temperature increase. Despite different absolute amounts of FF given between the two temperature levels, the WDTs were very similar at 6-7 days. Thus, it appears that a single temperature-independent WDT can potentially be assigned when the drug was applied at the optimal dosage.

Extended coverage of veterinary drug residues in food by LC-HRMS to ensure food compliance and prevent the spread of antimicrobial resistance

This study investigated the feasibility to monitor ca. 400 veterinary drug residues in various foodstuffs by a single method. For this, a generic QuEChERS-based approach was applied for sample preparation while liquid chromatography-high resolution mass spectrometry (LC-HRMS) was considered as detection technique. The LC-HRMS based method was eventually found suitable to screen for 353 parent compounds and marker residues in raw materials of animal sources (dairy-, meat-, fish-, egg-, and animal by-products), but also in related processed ingredients and end commercialized items. The screening approach was fully validated according to the European Guidelines in 70 samples, ending with false positive- and false negative rates below 5 %. Simultaneously, quantitative method performances were found acceptable in terms of recovery (70–120 % range) and precision (<20 %) for 184 out of the 353 compounds. A set of 114 samples originating from Europe, Asia, USA, Brazil, New Zealand and Australia, were subsequently analyzed to collect occurrence and quantitative data. The survey highlighted a high incidence of Antiparasitics (Benzimidazoles in eggs and Coccidiostats in poultry samples), though only one poultry sample for monensin (22 µg kg−1) exceeded the Maximum Residue Level set at 10 µg kg−1 by the European Union. The presented LC-HRMS approach was complemented with a dedicated LC-MS/MS method to improve quantitative measurements of such recurringly found Coccidiostats but also to achieve enhanced sensitivity for Macrocylic lactones.

Determination of temperature-dependent optimal oral doses of florfenicol and corresponding withdrawal times in Nile tilapia (Oreochromis niloticus) reared at 25 and 30°C

Antimicrobials are important tools for controlling bacterial outbreaks in aquaculture, but their misuse can bring more harms than benefits. For prudent use of antimicrobials, an optimal dosing regimen that is adjustable by rearing temperature and antimicrobial sensitivity are preferred over a universal dosage. The main objective of the present study was to investigate the advantage of using temperature-dependent optimal dosages of florfenicol (FF) on withdrawal time (WDT) reduction compared to a conventional recommended dosage in Nile tilapia. First, the pharmacokinetic (PK) parameters of FF at 25 and 30 °C were determined after a single oral administration of 10 mg/kg FF. Then, the optimal dosing regimens, calculated by the pharmacokinetic-pharmacodynamic (PK-PD) approach with a target minimum inhibitory concentration (MIC) of 3 μg/mL were used to evaluate tissue depletion and WDT. The optimal doses as determined by PK study were 4.46 and 12.60 mg/kg/day for 25 and 30 °C, respectively. Subsequently, the fish were orally administered with FF at the round-up optimal dosages (5 mg/kg/day at 25 °C and 13 mg/kg/day at 30 °C) or a general dosage (10 mg/kg/day at 25 °C) once daily for 5 days for tissue depletion and WDT study. The serum concentrations at 24 h after the last optimal dose were 3.26 (for the 5 mg/kg/day 25 °C) and 3.72 μg/mL (for the 13 mg/kg/day 30 °C), respectively, which were comparable to the target MIC of 3 μg/mL; whereas, the corresponding concentration of the general dosage at 25 °C was 8.06 μg/mL. Using the sum of FF and its major metabolite florfenicol amine (FFA) as the marker residue in the muscle/skin and the maximum residue limit (MRL) of 1 μg/g, the WDT for general dosage was 10 days, whereas those of the optimal dosages were 7–8 days. The current study revealed that overdosing may occur at lower while under-dosing could happen at higher rearing temperature if single general dosage was employed. With the established optimal dosing regimen, serum concentrations could be maintained above the target MIC and the WDT be shortened, a single WDT might be possible using the optimal dosages strategy regardless of water temperature.

Accumulation and biotransformation of the novel vanillin-derived pesticide, vanisulfane, in laying hens after dietary exposure

Vanisulfane is a novel plant antiviral agent with promising prospects to prevent and control viral crop diseases. However, human health risk assessment after vanisulfane exposure from animal-derived food products remains limited. To gain insight into the accumulation and biotransformation of vanisulfane in livestock, laying hens were dietary exposed to 14C-vanisulfane. Although more than 80 % of the applied dose was observed in the excreta, vanisulfane and its metabolites accumulated in tissues, especially the liver and kidney, and was found to be transferred to eggs. A total of eight metabolites associated with both phase I and phase II metabolism were identified via 14C tracing and LC–QTOF–MS. Phase I metabolism included oxidation, hydroxylation, dechlorination and demethylation, and phase II metabolism was associated with sulfonic acid and glucuronide conjugation. The high percentages of metabolites in laying hens’ tissues and organs, illustrated the active biotransformation of vanisulfane in vivo, which suggests that the marker residues of vanisulfane should consider its major metabolites. A digestive model was also used to determine the digestive fate of vanisulfane. This study improves our understanding of vanisulfane accumulation and biotransformation in laying hens, which will be helpful for risk assessments of foods derived from animals exposed to pesticides.

Temperature-dependent tissue residue depletion and withdrawal time of orally administered tylosin tartrate in starry flounder, Platichthys stellatus

The purpose of this study was to demonstrate the effect of water temperature on residue depletion and withdrawal times (WTs) of tylosin in serum, muscle plus skin, liver, and kidney of the starry flounder, Platichthys stellatus, post oral (PO) administration of tylosin tartrate (TT) at 10 mg/kg dosage for 5 consecutive days. Samples were taken 3, 5, 7, 14, and 21 days post last dose, and tylosin was quantified using liquid chromatography-tandem mass spectrometer (HPLC-MS/MS). The elimination half-life (T1/2) for each tissue was calculated using ln2/k and the WT was calculated using the WT 1.4 software at 99% statistical tolerance limit with 95% confidence. High concentrations of tylosin were detected in liver and kidney samples. A decrease in water temperature from 22 to 13 °C prolonged the T1/2 in all the tissue samples. The T1/2 were 1.82 and 6.19 d in serum, 2.63 and 3.92 d in muscle plus skin, 4.53 and 13.59 d in liver, and 10.83 and 28.88 d in kidney at 22 and 13 °C, respectively. The WTs for tylosin in the kidney, liver, muscle plus skin, and serum samples were in the following order: 111.7 d > 50.7 d > 20.1 d > 0 d at 22 °C and > 120 d > 81.3 d > 27.9 d > 0 d at 13 °C, respectively. Furthermore, WT (with T1/2) and water temperature were negatively correlated, in all the tissue samples. Further, our results suggest a WT of 28 d for TT (marker residue; tylosin A) in the muscle plus skin tissue (target tissue) of P. stellatus for its safe consumption. Overall, our study provides a theoretical basis for the effect of water temperature on the drug residue pattern and elimination kinetics of PO administered TT in P. stellatus, which is important for improving food safety in farmed fish.