Residue Depletion Study Research Articles

Application potential of albendazole as an aquatic animal drug based on its safety, efficacy, and residue profiles.

The number of available drugs for treating aquatic animals is insufficient, given the occurrence of a variety of parasites and difficulties in developing appropriate treatments, such as vaccines or immunostimulants. Consequently, repurposing livestock drugs for treating aquatic animals is a viable alternative. Several studies have demonstrated that albendazole (ABZ) is a good anthelmintic for humans and animals such as ruminants, poultry, and honeybees. Therefore, we investigated the toxicological studies, metabolic and residue depletion studies, and efficacy trials of ABZ in aquatic animals to identify its application potential as a drug for aquatic animals. ABZ was depleted within 24h in the muscle tissues of hybrid striped bass, rainbow trout, and tilapia. In muscle tissue with adhering skin obtained from tilapia and largemouth bass, a significant quantity of the amino-sulfone metabolite of ABZ (ABZ-SO2NH2) was present, while no ABZ-SO2NH2 was detected in hybrid striped bass, channel catfish, and patinga. Fish exposed only to high doses of ABZ showed reduced red blood cell counts and hemoglobin levels and increased lymphocytes. Such signs of toxicity have also been observed in human patients and animal studies. At a dose of 100mg/L, ABZ showed 100% efficacy in eels. In addition, albendazole sulfoxide (ABZSO) demonstrated efficacies of 96.1% and 100% in pirapatinga and ray-finned fish, respectively, at a dose 500mg/L. ABZ was also highly effective in treating an intracellular parasite E. hepatopenaei in white shrimp. The application of ABZ in aquatic animals under the low-dose and short-term conditions is considered a reasonable solution to manage parasite infections. The types and residual periods of degradation products differed among fish species, suggesting dissimilar metabolic pathways. With a high demand for new alternative veterinary drugs in aquaculture by fish farmers, this review offers important evidence for considering the use of ABZ in Korean farmed fish, taking food safety issues into account.

Pharmacokinetics of long-acting cephapirin and cloxacillin after intramammary administration in dairy goats.

Determining the pharmacokinetics of intramammary antimicrobials in goats can assist in predicting appropriate meat and milk withdrawal intervals for drugs that are effective at treating subclinical mastitis due to non-aureus Staphylococci during the dry period. Twenty-four healthy, lactating does were enrolled in this study. Half were administered 300 mg of cephapirin benzathine (ToMORROW, Boehringer Ingelheim Vetmedica, Duluth, GA) via intramammary infusion into each half of the udder. The remaining does had 500 mg cloxacillin benzathine (Orbenin DC, Merck & Co., Rahway, NJ) administered per half. Plasma was collected before treatment and for 7 days post-treatment followed by analysis via liquid chromatography with tandem mass spectroscopy. Pharmacokinetic parameters were determined using noncompartmental methods via commercial software (MonolixSuite). The mean maximum concentration (Cmax) of cephapirin of 0.073 μg/mL was noted at 7.06 h post-administration (Tmax). The area under the plasma concentration curve based on the final sampling point (AUClast) was 1.06 h × μg/mL. The mean residence time until the final sampling point (MRTlast) was 13.55 h. Mean terminal half-life (T½) of cephapirin was 6.98 h. In CLOX does, Cmax was 0.074 μg/mL with a Tmax of 18 h, AUClast was 5.71 h × μg/mL, T½ was 77.45 h, and MRTlast was 65.36 h. Despite both products being formulated with benzathine salts, marked differences were noted in pharmacokinetic parameters including AUC, T1/2, and MRTlast. This data will be used to plan sampling schedules for milk and tissue residue depletion studies for both products.

The pharmacokinetic and residue depletion study of eugenol in carp (Cyprinus carpio).

The pharmacokinetic profile and residue depletion of eugenol in carp (Cyprinus carpio) tissues and plasma were performed by a convenient and reliable high-performance liquid chromatography (HPLC) method. The eugenol in carp tissues and plasma was extracted with a mixed solution of acetonitrile and methanol. N-hexane was used to remove lipid impurities. The method was successfully applied to the pharmacokinetic and residue elimination of eugenol in carp after the carp was administered a medicated bath. The average recoveries of eugenol in tissues and plasma fortified with four concentration levels were 69.0-106.6% and 80.0-86.7%, respectively. The relative standard deviations were < 8.9%. The limit of detection (LOD) was 0.01 μg/g in tissue and 0.008 μg/ml in plasma, respectively. The pharmacokinetic parameter of Cmax for eugenol in plasma at the concentrations of 20, 35, and 75 mg/L were 10.86, 17.21, and 37.32 mg/L, respectively. The t1/2 values were 3.68, 4.22, and 9.31 h. After the investigation of the anesthetic effect, 35 mg/L of eugenol was the optimal concentration for anesthesia. The highest accumulation concentration of eugenol in carp is in the liver and the lowest is in the muscle. In addition, the eugenol in tissue was eliminated rapidly and at a lower level than the LOD at 48 h. According to the residue elimination, the withdrawal time of eugenol was suggested at 5.2 days. These results indicate that the developed method had good linearity and accuracy, and is sensitive enough for the monitoring of eugenol residue in carp. The half-life of eugenol decreased with the increase in drug concentration and the eugenol was eliminated rapidly in carp tissues. 35 mg/L eugenol was recommended as an anesthetic in carp due to its favorable anesthetic effect and no mortality. This study will contribute to the establishment of MRL regulation and setting a withdrawal period.

The multicomponent residue depletion of Gelsemium elegans in pig tissues, urine, and plasma.

Gelsemium elegans (G. elegans) as a traditional medicinal plant used in livestock production. The use of G. elegans in veterinary clinics may pose safety risks to human health. The aim of this study was to investigate tissue residue depletion in pigs fed G. elegans powder. A precise quantitation method and a simultaneous semi-quantitation method for multiple components independently of standards in pig tissues were developed for the first time. The two methods were validated in terms of specificity, LODs, LOQs, linearity, accuracy, precision, and matrix effects. They were then applied to a tissue residue depletion study after G. elegans powder at a dose of 2% per kg feed were fed to pigs. Compared with precise quantitation, the method validation results indicated that the semi-quantitation method was reliable and acceptable for multicomponent quantification independent of standards. Many G. elegans alkaloids are widely distributed in most tissues of pigs. Tissue residue depletion studies indicated that 14-hydroxygelsenicine, 11-hydroxygelsenicine, and gelsemoxonine could be used as potential residue markers, and pancreas, small intestine, and lung tissues could be considered as potential residue target tissues of G. elegans. In addition, both urine and plasma could be used to predict 14-hydroxygelsenicine and gelsemoxonine residues in the liver, pancreas, and small intestinal tissues of pigs. The developed semi-quantification method can be applied to monitor the application and residue of G. elegans. The results provide scientific evidence for evaluating the safety of animal-derived food from G. elegans for consumers and will be helpful for its application and future development.

Fipronil and its metabolites in chicken feather: residue analysis, depletion study, and application analysis of pollution sources in laying hens.

A method based on a multi-mechanism impurity adsorption and ultra-performance liquid chromatography-tandem mass spectrometry was established to detect fipronil and four of its metabolites in chicken feathers. This method was successfully applied to the depletion study of fipronil in feathers of laying hens. Fipronil and two metabolites were found in feathers during treatment. Fipronil concentrations in feathers increased during medication and then regularly decreased during withdrawal, and they were still detected on the 14th day after withdrawal. High residue concentrations were also present in feathers on day 23 of the experimental period. Pollution sources of fipronil can be inferred on the basis of the residue ratio of fipronil metabolites from different pollution modes. Result shows that feathers were an effective matrix for residue monitoring and risk analysis of fipronil in animals and the environment.

Professor Susanne Rath, a researcher who has bravely faced challenges since childhood, kindly granted BrJAC an interview

Susanne Rath is an associate professor in the Institute of Chemistry at the University of Campinas (Unicamp), where she coordinates the “Laboratório de Bioanalítica Paracelsus”. She graduated with a Bachelor's degree in Chemistry (1983) from the University of Brasília (UnB), a Master’s degree in Chemistry (1986) from Unicamp, and a Ph.D in Pharmaceutical Chemistry (1990) from the Johann Wolfgang Goethe Universität Frankfurt am Main, Germany. So far, she has published 110 articles and seven book chapters, had four patents granted, and she has presented over 230 papers at scientific conferences. She supervised 17 master's students, 20 doctorate students and 10 post-docs. In addition, she coordinated 23 research projects supported by Brazilian funding agencies. Prof. Dr. Rath’s primary research is focused on toxic compounds in food, residue depletion studies of veterinary drugs in food-producing animals, development and validation of analytical methods, application of bidimensional chromatography and mass spectrometry, environmental impact assessment of veterinary drugs, antimicrobial resistance and N-nitrosamines in food, cosmetics and drugs. Since 2007, Prof. Rath has been a member of the Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO). Since 2011, Prof. Rath has been a member of the Technical Group on Maximum Residue Limits for Veterinary Drugs in Food of the National Health Surveillance Agency (Anvisa) of the Ministry of Health of Brazil.

Excretion, Metabolism, and Tissue Distribution of Gelsemium elegans (Gardn. & Champ.) Benth in Pigs.

Gelsemium elegans (Gardn. & Champ.) Benth is a toxic flowering plant in the family Loganiaceae used to treat skin diseases, neuralgia and acute pain. The high toxicity of G. elegans restricts its development and clinical applications, but in veterinary applications, G. elegans has been fed to pigs as a feed additive without poisoning. However, until now, the in vivo processes of the multiple components of G. elegans have not been studied. This study investigates the excretion, metabolism and tissue distribution of the multiple components of G. elegans after feeding it to pigs in medicated feed. Pigs were fed 2% G. elegans powder in feed for 45 days. The plasma, urine, bile, feces and tissues (heart, liver, lung, spleen, brain, spinal cord, adrenal gland, testis, thigh muscle, abdominal muscle and back muscle) were collected 6 h after the last feeding and analyzed using high-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. Five natural products in plasma, twelve natural products and five metabolites in urine, and three natural products in feces were characterized, suggesting that multiple components from G. elegans were excreted in the urine. However, ten natural products and four metabolites were detected in bile samples, which suggested that G. elegans is involved in enterohepatic circulation in pigs. A total of seven of these metabolites were characterized, and four metabolites were glucuronidated metabolites. Ten natural products and six metabolites were detected in the tissues, which indicates that G. elegans is widely distributed in tissues and can cross the blood-brain barrier. Among the characterized compounds, a highly toxic gelsedine-type alkaloid from G. elegans was the main compound detected in all biological samples. This is the first study of the excretion, metabolism and tissue distribution of multiple components from G. elegans in pigs. These data can provide an important reference to explain the efficacy and toxicity of G. elegans. Additionally, the results of the tissue distribution of G. elegans are of great value for further residue depletion studies and safety evaluations of products of animals fed G. elegans.

Determination and Identification of Nicarbazin, Measured as 4,4'-Dinitrocarbanilide (DNC), in Chicken Tissues by Liquid Chromatography With Tandem Mass Spectrometry: Final Action 2013.07.

BackgroundAOAC Method 2013.07 was adopted as First Action in 2013. Since then, the method has been used in numerous residue depletion studies with favorable comments from analysts.ObjectiveTo analyze data from residue depletion studies to support Final Action status.MethodTen residue depletion studies were conducted during May 2014 through May 2019. For each study, harvested incurred tissues were analyzed for nicarbazin using AOAC Method 2013.07 in 1 of 4 laboratories. Each analytical run included one or more fortified quality control test portions. The data from these known fortified matrix test portions were analyzed for reproducibility and repeatability.ResultsFor muscle tissues, relative recovery was 90.4% (95% CI 83.8 to 97.5); RSDr was 5.4% (95% CI 3.8 to 9.2); and RSDR was 7.9%. In the liver, values were 94.5% (95% CI 91.1 to 98.0), 5.8% (95% CI 4.1 to 9.9), and 6.8%, respectively. In the kidney, values were 91.5% (95% CI 85.3 to 98.1), 5.2% (95% CI 3.7 to 8.8), and 9.0%, respectively. In skin with adhering fat, values were 94.5% (95% CI 89.2 to 100.1), 8.9% (95% CI 6.3 to 15.1), and 8.9%, respectively. In all cases, repeatability and reproducibility were within acceptable limits.ConclusionsThe data and positive feedback support the transition of AOAC Method 2013.07 from First Action to Final Action.HighlightsFinal action status is supported by data collected during routine use of the method rather than a traditional multi-laboratory collaborative study. Data were subjected to statistical analysis using the pC-metamer, and then transformed back to the traditional C-metamer.

Determination of zilpaterol in a residue depletion study using LC-MS/MS in cattle plasma, muscle, liver and kidney

Zilpaterol is a β-agonist compound which promotes fat loss and muscle gain in cattle, providing economic benefits. However, zilpaterol residues in the animal might introduce a significant risk to humans after consumption. In the present manuscript, a highly specific, sensitive method using Selected Reaction Monitoring (SRM) in positive electrospray ionization (ESI +) mode by liquid chromatography coupled to triple quadrupole mass spectrometry (LC-MS/MS) for plasma, muscle, liver and kidney is presented. For method development, composition of the aqueous mobile phase, precipitation agent, and solid phase extraction (SPE) conditions were optimized. The method was fully validated showing a good linearity and recovery average greater than or equal to 97 % for all matrices. The method was applied to residue depletion studies in cattle after withdrawal of zilpaterol supplementation at 3, 4, 5 and 6 days showing that tissues can be consumed by humans after 4th day of zilpaterol withdrawal.

Depletion of oxytetracycline plus epi-oxytetracycline residues in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) under field conditions in Chile

The objective of this research study was to estimate the withdrawal time (WT) for oxytetracycline (OTC), administered intraperitoneally to two species of salmonids, rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). This was done in salmonid farms during the fattening phase in seawater, under field conditions. Seven cages from different marine farms were included, each as an experimental unit, treated with an intraperitoneal dose of OTC (in a range from 20 to 35 mg kg−1). From each sea cage, 10 fishes were randomly selected for laboratory analysis at each sampling point after treatment, which were variable according to the harvest of each cage. All selected fish were treated with a single dose of two different commercial OTC formulations; Formulation A (OTC 30%) and Formulation B (OTC 20%), both extra label. Study was performed according to VICH GL 57 guideline. Samples were kept cold until laboratory analysis. Homogenized samples were analyzed using a mass triple quadrupole spectrometer (Waters®, Xevo TQ-S micro). The analytical method was optimized for use in the laboratory and an internal validation procedure was performed following European Commission Decision 2002/657/EC for linearity, recovery and precision. The detection range, including the limit of detection (LOD) and limit of quantification (LOQ), were calculated according to VICH GL49 guidance.According to the degree days obtained from the residue depletion study and those observed in the last sampling, most of the sampled cages had concentrations that allow the veterinary drug to be suitable for a market with a maximum residue limit (MRL) value of 200 μg kg−1, but not for a market with an MRL of 10 μg kg−1, as might be expected, regardless of the dose and commercial veterinary drug used. Depending on the considered MRL, withdrawal times ranged from 5390 to 1676- and 4061–1641-degree days, for rainbow trout and Atlantic salmon, respectively. These estimates, obtained from field samples, can provide references regarding the WTs that must be considered in order to avoid the presence of OTC + 4-epi-OTC residues in Atlantic salmon and rainbow trout fillets, and thus protect the consumer health. Further studies are needed to assess the impact of other factors on WT under field conditions in different salmonid species.

Determination of veterinary antibiotics in cow milk using rotating-disk sorptive extraction and liquid chromatography

A novel application of rotating disk sorptive extraction (RDSE), using a styrene-divinylbenzene (S-DVB) sorbent for the extraction of antibiotic residues in milk was developed. The analytes studied were oxytetracycline and its 4-epimer, enrofloxacin, ciprofloxacin, sulfadoxine and trimethoprim. After RDSE, the analytes were determined by performing both high-performance liquid chromatography coupled to diode array detection (HPLC-DAD) and ultrahigh-performance liquid chromatography coupled to ultraspray-electrospray-time of flight-mass spectrometry (UPLC-TOF/MS).By using HPLC-DAD, the absolute recoveries were between 85.5% and 106.4% with relative standard deviations between 3.7% and 9.9%. The obtained limits of quantification (LOQs) were lower than the respective maximum residue levels (MRLs) reported for each analyte, demonstrating that the methodology was applicable for residue depletion studies. UPLC-TOF/MS showed absolute recoveries from 88.5% to 114.1%, with RSDs between 4.3% and 15.4%. The LOQs obtained using UPLC-TOF/MS were also lower than the MRLs for each respective analyte.Compared with other analytical methods previously reported for some of the analytes, the present method is simpler and less expensive and utilizes green chemistry, all while providing comparable figures of merit.

Pharmacokinetics of danofloxacin in rainbow trout after different routes of administration

The pharmacokinetics of danofloxacin was studied in rainbow trout (Oncorhynchus mykiss) after single administration by intravenous (IV), intramuscular (IM) and oral (OR) gavage at a dose of 10 mg/kg and by 10 mg/L bath for 2 h at 11.7 ± 0.8 °C. Furthermore, minimal inhibitory concentrations (MICs) of danofloxacin against a pathogenic strain of Yersinia ruckeri, Pseudomonas spp., and Aeromonas hydrophila were determined. Plasma concentrations of danofloxacin were determined using high-performance liquid chromatograph - UV and further subjected to noncompartmental analysis. Elimination half-lives for IV, IM, OR and bath administration were 25.97 h, 42.43 h, 41.04 h and 40.41 h, respectively. Peak plasma concentrations (Cmax) for IM, OR and bath administration were 3.64 ± 0.12, 2.93 ± 0.23, and 0.36 ± 0.02 μg/mL, respectively. Bioavailability was 105.87% (IM), 96.92% (OR) and 10.09% (bath). MIC values were 0.02 μg/mL for Y. ruckeri, 3.2 μg/mL for Pseudomonas spp., and 8 μg/mL for A. hydrophila at 12 °C. Danofloxacin provides the desired AUC0–24/MIC (≥125) and Cmax/MIC (≥10) values for Y. ruckeri following administration at a dose of 10 mg/kg (L) from all routes administration, whereas inadequate for Pseudomonas spp. and A. hydrophila. This information may help in the use of danofloxacin in rainbow trout, but increasing doses pharmacokinetics with the residue depletion study and clinical studies in infected fish are needed.

A reliable, simple and cost-efficient TLC-HPLC method for simultaneously determining florfenicol and florfenicol amine in porcine urine: application to residue surveillance

ABSTRACT Violative residues of florfenicol (FF) in porcine edible tissues pose a potential risk for human health. In this study, urine was selected as target matrix for routine residue monitoring of FF in pig, and a thin layer chromatography (TLC)-high-performance liquid chromatography (HPLC) method was developed for simultaneously determining FF and florfenicol amine (FFA) in porcine urine. The urine samples were extracted with ethyl acetate under alkaline environment. The extracts were enriched through evaporation, purified by TLC and analysed by HPLC at 225 nm. A Waters Symmetry C18 column was used for the separation of the two analytes. The mobile phase was acetonitrile-phosphate buffer mixtures (33.3: 66.7, v/v), and was pumped at 0.6 mL/min. The TLC-HPLC method was well validated and successfully applied to residue depletion study. Good analytical specificity was confirmed by the lack of interfering peaks at the retention times of FF and FFA. The standard curves showed good linearity (FF: y = 143064x – 1045.3, r= 0.9999; FFA: y = 275826x + 1888.8, r= 0.9999) over the range of 0.0625–8 μg/mL. The precision ranged from 0.83% to 11.66% and 2.19% to 8.75% for intraday and interday determination, respectively. The corresponding accuracy ranged from −13.38% to 10.78% and −12.15% to 7.14%, respectively. The limits of quantification (LOQs) for FF and FFA were 0.125 μg/mL. The residue depletion study showed that the concentrations of FF and FFA in urine were higher than those in edible tissues at three time points. This method was reliable, simple and cost efficient, and could be used to monitor FF residues in porcine edible tissue without slaughtering animals. TLC showed excellent purification efficiency and is expected to solve matrix interferences in veterinary drug residue analysis.

Determination of cephalexin residual level using ultra-high-performance liquid chromatography-tandem mass spectrometry: Residue depletion study in swine

An ultra-high-performance liquid chromatography-tandem mass spectrometry method was developed to analyze cephalexin in swine tissues, urine, and feces. Samples were extracted with 1% sulfuric acid, followed by purification using MCX cartridges. Mean recoveries were 95.4%–100.7% with inter-day relative standard deviations of <8.6%. The quantitation limit was 5 μg/kg for fat and urine, and 10 μg/kg for muscle, liver, kidney, and feces. Cephalexin residue depletion was determined using 32 healthy pigs, randomly divided into eight (seven treated and one control) groups. Treated groups were intramuscularly administered 10 mg/kg b.w. five times at 24-h intervals and euthanized 6 h and 1, 2, 3, 5, 7, and 10 days after the last injection. Cephalexin was eliminated rapidly in swine muscle, liver, fat, and feces. The highest concentrations among edible organs were detected in the kidney. Moreover, the longest elimination period of cephalexin in swine was determined in urine. These results indicated that kidney and urine were likely target matrices for cephalexin residue detection in swine.

Assessing Global Human Exposure to T-2 Toxin via Poultry Meat Consumption Using a Lifetime Physiologically Based Pharmacokinetic Model.

Residue depletion of T-2 toxin in chickens after oral gavage at 2.0 mg/kg twice daily for 2 days was determined in this study. A flow-limited physiologically based pharmacokinetic (PBPK) model was developed for lifetime exposure assessment in chickens. The model was calibrated with data from the residue depletion study and then validated with independent data. A local sensitivity analysis was performed, and 16 sensitive parameters were subjected to Monte Carlo analysis. The population PBPK model was applied to estimate daily intake values of T-2 toxin in different countries based on reported consumption factors and the guidance value of 0.25 mg/kg in feed for chickens by the European Food Safety Authority (EFSA). The predicted daily intakes in different countries were all lower than the EFSA's total daily intake, suggesting that the EFSA's guidance value has minimal risk. This model provides a foundation for scaling to other mycotoxins and other food animal species.

A Convenient and Sensitive LC-MS/MS Method for Simultaneous Determination of Carbadox- and Olaquindox-Related Residues in Swine Muscle and Liver Tissues

This paper presents a convenient and sensitive LC-MS/MS method for the simultaneous determination of carbadox and olaquindox residues, including desoxyolaquindox (DOLQ), desoxycarbadox (DCBX), quinoxaline-2-carboxylic acid (QCA), 3-methyl-quinoxaline-2-carboxylic acid (MQCA), and the glycine conjugates of QCA and MQCA (namely, QCA-glycine and MQCA-glycine, resp.) in swine muscle and liver tissues. Tissue samples were extracted with 2% metaphosphoric acid in 20% methanol and cleaned up by solid-phase extraction (SPE) on a mixed-mode anion-exchange column (Oasis MAX). Analysis was performed on a C18 column by detection with mass spectrometry in the multiple reaction monitoring (MRM) mode. The limits of detection (LODs) of the six analytes were determined to be 0.01 μg·kg−1 to 0.25 μg·kg−1, and the limits of quantification (LOQs) were 0.02 μg·kg−1 to 0.5 μg·kg−1. The total recoveries of the six analytes in all tissues were higher than 79.1% with the RSD% less than 9.2%. The developed method can determine the real residue level of QCA and MQCA, whether they are present in free form or as glycine conjugates in tissues, together with the carcinogenic desoxy metabolites DCBX and DOLQ with high recovery. Therefore, this method was suitable for routine analysis of residue control programmes and the residue depletion study of CBX and OLQ on swine.

Multiresidue Method for Quantification of Sulfonamides and Trimethoprim in Tilapia Fillet by Liquid Chromatography Coupled to Quadrupole Time-of-Flight Mass Spectrometry Using QuEChERS for Sample Preparation

A multiresidue method for detecting and quantifying sulfonamides (sulfapyridine, sulfamerazine, sulfathiazole, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfamethoxypyridazine) and trimethoprim in tilapia fillet (Oreochromis niloticus) using liquid chromatography coupled to mass spectrometry was developed and validated. The sample preparation was optimized using the QuEChERS approach. The chromatographic separation was performed using a C18 column and 0.1% formic acid in water and acetonitrile as the mobile phase in the isocratic elution mode. Method validation was performed based on the Commission Decision 2002/657/EC and Brazilian guideline. The validation parameters evaluated were linearity (r ≥ 0.99); limits of detection (LOD) and quantification (LOQ), 1 ng·g−1 and 5 ng·g−1, respectively; intraday and interdays precision (CV lower than 19.4%). The decision limit (CCα 102.6–120.0 ng·g−1 and 70 ng·g−1 for sulfonamides and trimethoprim, respectively) and detection capability (CCβ 111.7–140.1 ng·g−1 and 89.9 ng·g−1 for sulfonamides and trimethoprim, respectively) were determined. Analyses of tilapia fillet samples from fish exposed to sulfamethazine through feed (incurred samples) were conducted in order to evaluate the method. This new method was demonstrated to be fast, sensitive, and suitable for monitoring sulfonamides and trimethoprim in tilapia fillet in health surveillance programs, as well as to be used in pharmacokinetics and residue depletion studies.

Moxidectin residues in lamb tissues: Development and validation of analytical method by UHPLC-MS/MS.

The development and validation of a throughput method for the quantitation of moxidectin residues in lamb target tissues (muscle, kidney, liver and fat) was conducted using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). To achieve higher recovery of the analyte from the matrices, a modified QuEChERS method was used for sample preparation. The chromatographic separation was achieved using a Zorbax Eclipse Plus C18 RRHD column with a mobile phase comprising 5mM ammonium formate solution +0.1% formic acid (A) and acetonitrile +0.1% formic acid (B) in a linear gradient program. Method validation was performed based on the Commission Decision 2002/657/EC and VICH GL49. To quantify the analyte, matrix-matched analytical curves were constructed with spiked blank tissues, with a limit of quantitation of 5ngg-1 and limit of detection of 1.5ngg-1 for all matrices. The linearity, decision limit, detection capability accuracy, and inter- and intra-day repeatability of the method are reported. The method was successfully applied to incurred lamb tissue samples (muscle, liver, kidney and fat) in a concentration range from 5 to 200μgkg-1, which demonstrated its suitability for monitoring moxidectin residues in lamb tissues in health surveillance programs, as well as for pharmacokinetics and residue depletion studies.

Improving the selectivity and sensitivity for quantifying 8-α-hydroxy-mutilin in rabbit tissues by using basic mobile phases and negative ionization.

Previously reported LC-MS methods for quantifying 8-α-hydroxy-mutilin (a marker residue of tiamulin) in tissues all used a pseudo MRM transition (from protonated molecular ion to protonated molecular ion, m/z 337→337) due to difficulties in finding a product ion, leading to suboptimal selectivity and sensitivity for detection. By using electrospray negative ionization in a basic medium, we, for the first time, found a highly selective and sensitive true MRM transition for 8-α-hydroxy-mutilin, m/z 335→179. With this newly found MRM transition and the use of pleuromutilin as the internal standard, a very sensitive, selective, and robust LC-MS/MS method has been developed and validated for quantifying 8-α-hydroxy-mutilin in rabbit tissues (muscle, liver, kidney, and fat). In comparison with the previously published methods, the selectivity and sensitivity were significantly improved. For the concentration range validated (0.2-10ppm or 0.2-10μg/g), the within-run and between-run accuracies (% bias) ranged from -5.0 to 3.1 and -4.9 to 3.0, respectively. The% CV ranged from 2.2 to 6.6 and 4.7 to 8.3 for within-run and between-run precisions, respectively. The validated method was successfully used to support two GLP tissue residue depletion studies in rabbits.

Disposition and Residue Depletion of Metronidazole in Pigs and Broilers

Metronidazole (MNZ) is used in veterinary medicine for the treatment of anaerobic infections and a variety of protozoal and parasitic diseases. Current study has been conducted to examine the disposition and residue depletion studies of MNZ and its main metabolites in pigs and broilers. After a single oral administration of MNZ, the concentrations of MNZ and its main metabolites in the excreta of pigs and broilers were determined by LC-MS/MS. More than 75% of the drug was recovered within 14 days, of which MNZ accounted for about 40%, MNZ-OH 20–25% and MAA less than 10%. The residue depletion study showed that MNZ was the most predominant residue in all of the tissues and could be detected in liver, kidney and muscle up to the withdrawal time of 14 days. MNZ-OH concentrations were lower than MNZ in all of the tissues, but its elimination half-life was close to MNZ. It is proposed that kidney and muscle are appropriate residue target tissues and both MNZ and its hydroxylated metabolite, MNZ-OH, should be monitored in the routine surveillance of MNZ related residues in food of animal origin.