Tissue Residue Depletion Research Articles

Tissue distribution and residue depletion of difloxacin in crucian carp (Carassius carassius) after multiple oral administration

Although difloxacin is not listed by Codex or the US FDA, China and some countries in Asia have approved this drug for use in aquaculture. Additionally, both China and EMA have adopted the same maximum residue limit (MRL) for difloxacin in muscle plus skin at 0.3 μg/g. However, a withdrawal period has not been established for difloxacin in aquaculture. Therefore, the primary goal of this investigation was to evaluate the tissue distribution and residue depletion of difloxacin in crucian carp (Carassius carassius) kept in freshwater at a temperature of 21 ± 1 °C, with the aim of determining an appropriate withdrawal period. This investigation entailed the oral administration of difloxacin via gavage, employing a daily dosage of 20 mg/kg body weight (BW) over a consecutive three-day regimen. Diverse samples, including plasma, bile, skin-on-muscle, liver, kidney, intestine, and gill, were collected at predetermined time intervals after the final administration. The quantification of difloxacin concentrations in all collected samples was carried out utilizing a high-performance liquid chromatography (HPLC) method. Difloxacin exhibited extensive distribution within crucian carp, with detectable presence in all examined tissues. The highest average concentration was notably observed in the bile with a Cmax of 14.359 μg/mL. Remarkably, even on the 15th day (360 h) following the final dosing, traces of difloxacin residues remained detectable in all collected samples. Pharmacokinetic parameters, determined through the noncompartmental model, unveiled diverse elimination half-lives (t1/2λzs) for difloxacin across distinct samples, ranging from rapid to slow: plasma (9.46 days), skin-on muscle (10.15 days), liver (10.36 days), bile (13.05 days), intestine (20.94 days), kidney (22.12 days), and gill (29.56 days). Taking into consideration the MRL, a withdrawal period of 32 days was definitively determined, derived from the upper limit of the one-sided 95% confidence interval. When converted to the unit of °C-day, the withdrawal period was determined to be 660.

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.

In vitro antibacterial activity of danofloxacin against Escherichia coli in Gushi chickens and its residue depletion following multiple oral administration

This study aimed to investigate the in vitro antibacterial activity of danofloxacin against Escherichia coli isolated from Gushi chickens, as well as the tissue distribution and residue depletion of danofloxacin in Gushi chickens following multiple oral administration. A total of 42 clinical E. coli strains were isolated from the cloaca of locally farmed Gushi chickens between August and October 2023. Then the minimum inhibitory concentration (MIC) of danofloxacin against these isolates was determined by broth microdilution method. Additionally, 42 healthy Gushi chickens were randomly divided into 6 groups, and danofloxacin was orally administered at a dose of 5 mg/kg body weight (BW) for 3 consecutive days. Plasma, intestinal content, and tissue samples, including muscle, skin + fat, liver, kidney, lung, and intestine, were collected at 4, 12, 24, 48, 72, and 120 h after the last administration. Danofloxacin concentrations in all samples were determined using a high-performance liquid chromatography (HPLC) method. The average concentration vs. time data were then subjected to noncompartmental analysis using Phoenix software, and withdrawal periods for danofloxacin in Gushi chickens were further determined with WT1.4 software, setting a 95% confidence interval. Results indicated a notable inhibitory effect of danofloxacin on E. coli, with an MIC50 of 0.5 μg/mL. Additionally, danofloxacin exhibited widespread distribution in Gushi chickens, detectable in all collected samples. Among all tissues, the liver exhibited the highest concentration, followed by the intestine. Even on the fifth day postadministration, danofloxacin persisted in skin + fat, liver, and lung. The elimination half-lives (t1/2λzs) of danofloxacin varied across samples: skin + fat (47.87 h), lung (30.61 h), liver (22.07 h), plasma (16.05 h), muscle (12.53 h), intestine (9.83 h), and kidney (6.34 h). Considering residue depletion and the maximum residue limit (MRL) of danofloxacin in poultry set by Chinese regulatory authorities, withdrawal periods for the kidney, muscle, liver, and skin + fat were determined as 1.03, 1.38, 3.34, and 5.85 d, respectively, rounded to a final withdrawal time of 6 d.

Pharmacokinetics, tissue residue depletion, and withdrawal interval estimations of florfenicol in goats following repeated subcutaneous administrations

Florfenicol is a broad-spectrum antibiotic commonly used in the U.S. to treat respiratory and enteric infections in goats in an extra-label manner, which requires scientifically based withdrawal intervals (WDIs) for edible tissues. This study aimed to determine the depletion profiles for florfenicol and florfenicol amine in plasma and tissues samples and to estimate WDIs for goats following subcutaneous injection of 40 mg/kg florfenicol, twice, 96 h apart. The samples were collected up to 50 days after the second dose. Pharmacokinetic parameters were calculated using non-compartmental analysis. Three different pharmacostatistical methods with different operational tolerances were used to calculate WDIs. The plasma half-life was 101.80 h for florfenicol and 207.69 h for florfenicol amine after the second dose. Using the FDA tolerance limit method, WDIs were 202 and 101 days, while the EMA maximum residue limit method estimated 179 and 96 days for the respective tissue concentrations to fall below limits of detection (0.12 μg/g for liver and 0.05 μg/g for kidney). This study characterizes plasma pharmacokinetics and tissue depletion profiles of florfenicol and florfenicol amine in goats following subcutaneous injections and reports estimated WDIs for food safety assessment of florfenicol in goats.

Tissue residue distribution and withdrawal time estimation of trimethoprim and sulfachloropyridazine in Yugan black-bone fowl (Gallus gallus domesticus Brisson)

Black-bone fowl are different from ordinary broilers in appearance and are considered to have rich nutritional properties. However, the metabolism of therapeutic drugs in black-bone fowl remains unclear. This study aimed to determine the tissue residue depletion kinetics of trimethoprim and sulfachloropyridazine in Yugan black-bone fowl, after daily oral administrations for 5 days at 4 mg/kg bw/day trimethoprim and 20 mg/kg bw/day sulfachloropyridazine, and to calculate the withdrawal times. After consecutive oral administrations, the tissues (liver, kidney, muscle and skin/fat) were collected at each of the following time points (0.16, 1, 3, 5, 7, 9, 20, 30 and 40 days). A newly-devised LC-MS/MS method was used to analyse the concentrations of trimethoprim and sulfachlorpyridazine in target tissues. The results showed that sulfachloropyridazine was rapidly metabolised in broilers, and there was no residue in all tissues 3 days post-administration. The concentration of trimethoprim in black-bone fowl skin/fat is the highest, and its metabolism rate is low. After 40 days, the concentration of trimethoprim in skin/fat is still as high as 140.1 ± 58.0 μg/kg, exceeding the maximum residue limit. In order to protect consumers’ health, it is suggested that the withdrawal time of TMP in Yugan black-bone fowl is 69 days.

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.

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.

Pharmacokinetic profile, tissue residue depletion and anthelmintic efficacy of supramolecular fenbendazole

A supramolecular complex of fenbendazole (SFBZ) with polyvinylpyrrolidone (PVP) was created by mechanochemical processing to increase its anthelmintic efficacy and to reduce the dose of applied drugs. The aim of our research was to study the pharmacokinetic profile and tissue residue depletion of fenbendazole (FBZ) and its metabolites: sulfoxide and sulfone in sheep after SFBZ treatment by high-performance liquid chromatography with tandem mass spectrometric detection and to evaluate its efficacy against gastrointestinal strongylatosis of sheep in field trials. The results revealed that FBZ and its metabolites were detected in blood serum in 2 h after SFBZ administration and in 4–6 h after the administration of the basic – FBZ. Pharmacokinetic parameters of SFBZ and its metabolites were characterized by higher rate of absorption, concentration of the drug and longer retention times in the blood serum. The maximum concentration of FBZ and its metabolites was detected on the 3rd day in the organs and tissues of sheep that received SFBZ. Thus, in the liver, the content of FBZ was 4878.0 ng/g, sulfoxide and sulfone − 18682.4 and 2483.6 ng/g respectively while the indicators of the basic FBZ and its metabolites were tenfold lower. FBZ and its metabolites were not detected in the organs and tissues of sheep on the 16th day in animals treated with the basic drug and on the 21st day after SFBZ administration. In field trials SFBZ demonstrated a high anthelmintic activity against nematodosis of sheep. It showed 98.2% efficacy against nematodirosis and 99.0 % against other types of gastrointestinal strongylatosis at a dose of 2 mg/kg of active substance (a.s.). Efficacy of mechanical mixture and efficacy of FBZ substance was in 3.1–3.4 times lower in the same dose.

Temperature-Dependent Residue Depletion Regularities of Tiamulin in Nile Tilapia (Oreochromis niloticus) Following Multiple Oral Administrations.

The aim of this study was to investigate the effect of different water temperatures (19, 25, and 30°C) on tissue residue depletion of tiamulin in Nile tilapia (Oreochromis niloticus) after five consecutive days of oral administration at the dose of 20 mg/kg body weight and to calculate the corresponding elimination half-life (T1/2) and withdrawal times (WTs). After oral administration at scheduled 11 time points (1, 2, 3, 5, 7, 9, 12, 15, 20, 25, and 30 days), samples of plasma and tissues (muscle plus skin, liver, kidney, and gill) were collected. Tiamulin concentration in samples were determined by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). T1/2 was calculated by the equation: T1/2 = ln2/k. WT 1.4 software was used to calculate WT. The results showed that tiamulin was widely distributed in all tissue samples with the highest concentration in liver. At three different water temperatures, the T1/2 were calculated as 2.76, 2.13, and 1.64 days in plasma, 2.71, 1.85, and 1.31 days in muscle plus skin, 2.27, 1.70, and 1.50 days in liver, 2.84, 2.32, and 1.94 day in kidney, and 3.16, 2.42, and 1.74 days in gill, respectively. At 19°C, the order of WT is kidney (11.88 days) > liver (10.41 days) > gill (10.77 days) > plasma (8.83 days) > muscle plus skin (7.14 days). The WT for tiamulin at 25°C was in the following order: kidney (8.40 days) > liver (8.21 days) > gill (8.07 days) > plasma (7.24 days) > muscle plus skin (4.05 days). At 30°C, the WT dropped and shown as follows: gill (6.99 days) > kidney (6.51 days) > liver (6.29 days) > plasma (3.27 days) > muscle plus skin (2.92 days). The present investigations indicated that increasing the temperature from 19 to 30°C shortened T1/2 and WT of tiamulin in tilapia. To ensure the safety of fish consumption, the longest WT of tissues is suggested for tiamulin in Nile tilapia at the corresponding water temperature; i.e., WTs were 12 days at 19°C, 9 days at 25°C, and 7 days at 30°C, respectively. Overall, we intended to provide a theoretical basis for tissue residue depletion kinetics of tiamulin in fish and improve our understanding of the influence of the temperature on tissue residue depletion kinetics of tiamulin in fish.

A study to assess the correlation between plasma, oral fluid and urine concentrations of flunixin meglumine with the tissue residue depletion profile in finishing-age swine

BackgroundFlunixin meglumine (FM) was investigated for the effectiveness of plasma, oral fluid, and urine concentrations to predict tissue residue depletion profiles in finishing-age swine, along with the potential for untreated pigs to acquire tissue residues following commingled housing with FM-treated pigs. Twenty pigs were housed in groups of three treated and one untreated control. Treated pigs received one 2.2 mg/kg dose of FM intramuscularly. Before treatment and at 1, 3, 6, 12, 24, 36, and 48 h (h) after treatment, plasma samples were taken. At 1, 4, 8, 12 and 16 days (d) post-treatment, necropsy and collection of plasma, urine, oral fluid, muscle, liver, kidney, and injection site samples took place. Analysis of flunixin concentrations using liquid chromatography/tandem mass spectrometry was done. A published physiologically based pharmacokinetic (PBPK) model for flunixin in cattle was extrapolated to swine to simulate the measured data.ResultsPlasma concentrations of flunixin were the highest at 1 h post-treatment, ranging from 1534 to 7040 ng/mL, and were less than limit of quantification (LOQ) of 5 ng/mL in all samples on Day 4. Flunixin was detected in the liver and kidney only on Day 1, but was not found 4–16 d post-treatment. Flunixin was either not seen or found less than LOQ in the muscle, with the exception of one sample on Day 16 at a level close to LOQ. Flunixin was found in the urine of untreated pigs after commingled housing with FM-treated pigs. The PBPK model adequately correlated plasma, oral fluid and urine concentrations of flunixin with residue depletion profiles in liver, kidney, and muscle of finishing-age pigs, especially within 24 h after dosing.ConclusionsResults indicate untreated pigs can be exposed to flunixin by shared housing with FM-treated pigs due to environmental contamination. Plasma and urine samples may serve as less invasive and more easily accessible biological matrices to predict tissue residue statuses of flunixin in pigs at earlier time points (≤24 h) by using a PBPK model.

Pharmacokinetics and bioavailability of oral firocoxib in adult, mixed-breed goats.

Pharmacokinetic (PK) studies of oral firocoxib in large animal species have been limited to horses, preruminating calves, and adult camels. The aim of this study was to describe pharmacokinetics and bioavailability of firocoxib in adult goats. Ten healthy adult goats were administered 0.5mg/kg firocoxib intravenously (i.v.) and per os (p.o.) in a randomized, crossover study. Plasma firocoxib concentrations were measured over a 96-hr period for each treatment using HPLC and mass spectrometry, and PK analysis was performed. The p.o. formulation reached mean peak plasma concentration of 139ng/ml (range: 87-196ng/ml) in 0.77hr (0.25-2.00hr), and half-life was 21.51hr (10.21-48.32hr). Mean bioavailability was 71% (51%-82%), indicative of adequate gastrointestinal absorption of firocoxib. There were no negative effects observed in any animal, and all blood work values remained within or very near reference range at the study's conclusion. Results indicate that oral firocoxib is well-absorbed and rapidly reaches peak plasma concentrations, although the concentration also decreased quickly prior to the terminal phase. The prolonged half-life may suggest tissue accumulation and higher plasma concentrations over time, depending on dosing schedule. Further studies to determine tissue residue depletion, pharmacodynamics, and therapeutic concentrations of firocoxib in goats are necessary.

Tissue residue depletion and estimation of extralabel meat withdrawal intervals for tulathromycin in calves after pneumatic dart administration.

The objectives of this study were to evaluate the injection site pathology and determine tissue residue depletion of tulathromycin in calves following pneumatic dart administration and to calculate the associated extralabel withdrawal interval (WDI). Castrated male Holstein calves were injected with ~2.6 mg/kg tulathromycin via pneumatic dart administration. At 1 (n = 2), 6, 12, 18, and 24 d after drug injection (n = 3/time point), calves were euthanized, and muscle, liver, kidney, fat, and injection site samples were harvested and analyzed for tulathromycin concentrations using a LC-MS/MS method. Gross pathology and histopathology evaluations on the injection site samples were also performed. Pneumatic dart administration of tulathromycin caused severe localized lesions of hemorrhage and edema on days 1 and 6, as well as severe pathological reactions in the subcutaneous muscle on days 1, 6, and 12. Slight to moderate reactions were still observed in the majority of the skin or subcutaneous/muscle samples on day 24. Measured tulathromycin concentrations were converted to calculate the concentrations of the marker residue CP-60,300 by dividing a conversion factor of 1.4. The data were used to calculate extralabel WDIs based on the guidelines from U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). The results showed that tulathromycin concentrations were the highest in the liver (4,877.84 ± 65.33 µg/kg), kidney (5,819.52 ± 1,087.00 µg/kg), muscle (1,717.04 ± 140.35 µg/kg), injection site (51,884.05 ± 7,529.34 µg/kg), and fat (161.69 ± 36.48 µg/kg) at 6, 1, 1, 1, and 1 d, respectively, after treatment. Tulathromycin concentrations remained above the limit of quantification of 5 µg/kg in all tissues at 24 d. The calculated WDIs based on kidney data were 26 d using EMA method, 36 d using FDA method based on CP-60,300 data, and 45 d using FDA method based on tulathromycin data. These results suggest that pneumatic dart administration of tulathromycin causes injection site reactions in calves and an extended WDI is needed. One limitation of this study was the small sample size of 3 that did not meet FDA guideline requirement. Therefore, the calculated WDIs should be considered as preliminary and additional studies that use a larger number of animals and directly measure the concentrations of the marker residue CP-60,300 are needed to make a more conclusive recommendation on the extralabel WDI.

Tissue residue depletion kinetics and withdrawal time estimation of doxycycline in grass carp, Ctenopharyngodon idella, following multiple oral administrations

This study aimed to determine the plasma and tissue residue depletion kinetics of doxycycline (DC) in grass carp (Ctenopharyngodon idella) after daily oral administrations at 20 mg/kg for 3 days, and to calculate the corresponding withdrawal times. Following drug administrations, samples of plasma, liver, kidney, gill and muscle + skin were collected at predetermined time points (0.25, 0.5, 1, 3, 5, 7, 14, 21, 28, 35, 42, 49 and 56 days) and analyzed for concentrations of DC using a LC-MS/MS method. The results showed that liver had the highest concentrations and the slowest depletion compared to other tissues, with detectable DC up to 49 days (58.9 ± 12.8 μg/kg). The WT 1.4 software and “reschem” package were used to calculate withdrawal times, and the results were similar. The results suggest a withdrawal time of 41 days for Europe and China and 50 days for Japan is needed for DC in grass carp after 3 daily oral administrations at 20 mg/kg. Overall, this study improves our understanding of the tissue residue depletion kinetics of DC in fish, and the results may help regulatory agencies to determine proper withdrawal periods based on different regulatory standards in different countries to ensure safety of aquatic food products.

Tissue residue depletion of moxidectin in lambs (Ovis aries) following subcutaneous administration

ABSTRACTTo date, a tissue depletion study of moxidectin (MOX) in lambs is not available. Thus, considering that lamb meat is of great commercial interest in the world, the aim of the present study was to determine the residue levels of MOX in lamb target-tissues (muscle, liver, kidney and fat) and subsequently calculate the MOX withdrawal period. For this purpose, the target-tissues were analysed by ultra-high-performance liquid chromatography-tandem mass spectrometry. Method validation was performed based on Commission Decision 2002/657/EC and VICH GL49. To quantify the analyte, matrix-matched analytical curves were constructed with spiked blank tissues. The limits of detection and quantitation were 1.5 and 5 ng g−1, respectively, for all matrices. The linearity, decision limit, detection capability accuracy and inter- and intra-day precision of the method are reported. The lambs were treated with a single subcutaneous dose of 0.2 mg MOX kg−1 body weight and were slaughtered in accordance with accepted animal care protocols. Samples of target-tissues were collected on 2, 4, 7, 14, 28 and 42 days after MOX administration. During the whole study, the highest drug residue level occurred in the fat. For the other target-tissues (muscle, liver and kidney), MOX concentrations were below the maximum residue limit (MRL). Considering the MRL value of 500 µg kg−1 for MOX residues in sheep fat, our results in lambs allowed the estimation of a MOX withdrawal period of 31 days. This indicates that the withdrawal period established for MOX in adult sheep (28 days) does not apply for lambs.

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.

Pharmacokinetics of tulathromycin in edible tissues of healthy and experimentally infected pigs with Actinobacillus pleuropneumoniae

The aim of this study was the comparison of the tissue pharmacokinetics of tulathromycin in healthy pigs and pigs experimentally infected with Actinobacillus pleuropneumoniae (App). Tulathromycin was given to 24 healthy and 24 infected pigs by intramuscular injection at a single dosage of 2.5 mg kg−1 body weight (b.w.). Pigs were euthanised at each group and then samples of liver, kidney, muscle, injection site and skin with fat were taken at scheduled time points. Drug concentrations were determined by LC-MS/MS. In this study, higher values of the area under the concentration–time curves (AUC) were calculated in all tissue samples taken from infected than healthy pigs. In pigs with App the AUCs of liver, kidney, muscle, skin with fat and injection site were 1111, 1973, 235, 181 and 2931 mg kg−1 h, while in pigs without inflammation they were 509, 1295, 151, 111 and 1587 mg kg−1 h, respectively. Maximum drug tissue concentrations (Cmax) in infected animals were 2370, 6650, 2016, 666 and 83 870 µg kg−1, while in healthy pigs they were 1483, 6677, 1733, 509 and 55 006 µg kg−1, respectively. The eliminations half-times (T1/2) were respectively longer in all tissue samples taken from infected animals (from 157.3 to 187.3 h) than in healthy ones (from 138.6 to 161.2 h). The tulathromycin tissue concentrations were significantly higher (p < 0.05) in all tissue samples of the infected pigs compared with the healthy animals at 360 h (from 0.0014 to 0.0280) and at 792 h (from 0.0007 to 0.0242) after drug administration. The results suggest that the tissue pharmacokinetic properties and residue depletion of tulathromycin can be influenced by the disease state of animals.

Tissue distribution and residue depletion of metronidazole in rainbow trout (Oncorhynchus mykiss)

Tissue distribution and residue depletion of metronidazole (MNZ) was studied in rainbow trout (Oncorhynchus mykiss) following oral administration of MNZ in feed at the average dose of 25 mg kg−1 body weight day−1 for 7 days at 11 ± 2°C. The MNZ concentration in feed was 0.25% while daily feed intake was 1% of body weight. The concentrations of MNZ and its main metabolite, hydroxymetronidazole (MNZOH), in fish tissues were determined by LC-MS/MS. The drug was well distributed in tissues with maximum concentrations on day 1 post-administration. At this time, the mean MNZ concentrations in muscle, skin, kidney, liver and gill were 14 999, 20 269, 15 070, 10 102 and 16 467 µg kg−1 respectively. MNZ was converted into MNZOH with the ratio of MNZOH:MNZ up to 7% in all fish tissues throughout the withdrawal period. This shows that MNZ itself is the main residue in rainbow trout. MNZ was detected at the level close to the decision limit (0.20 µg kg−1) in muscle, skin and muscle with adhering skin up to 42 days, while in kidney, liver and gill it was up to 28 days post-administration. MNZOH was eliminated more rapidly from fish tissues and it was present in muscle alone up to 21 days. The elimination half-lives of MNZ and MNZOH in rainbow trout tissues were 1.83–2.53 and 1.24–2.12 days, respectively. When muscle without skin was analysed, higher MNZ and MNZOH concentrations were detected, and for a longer period of time, than in muscle with adhering skin. Thus muscle alone could be more appropriate for the effective residue control of MNZ in rainbow trout. For the same reason, it is also essential to ensure direct cooling immediately after sampling, since MNZ and its metabolite degrade in fish muscle and skin stored in non-freezing conditions.

Tissue deposition and residue depletion in rainbow trout following continuous voluntary feeding with various levels of melamine or a blend of melamine and cyanuric acid

This study determined the deposition and depletion in rainbow trout after continuous administration of melamine (MEL) alone or a blend of MEL and cyanuric acid (CYA). The plasma, muscles, kidneys, liver and gills were sampled at 0, 3, 7, 13, 21, 28 and 42d. After the final sampling at 42d, fish from the MEL0.05, MEL20 and MCA groups were fed the control diet (MEL0) for the depletion test. Co-administration with cyanuric acid accelerated the deposition time to the Css for melamine; during the withdrawal phrase, the melamine and CYA concentrations in the tissues decreased exponentially. Compared to the t1/2 for single oral administration, the t1/2 for melamine and cyanuric acid after 42d continuous feeding was prolonged. The presence of trace CYA in the plasma and kidneys of trout was detected in the MEL20 group, indicating that MEL can convert into CYA in rainbow trout.

Depletion of penicillin G residues in heavy sows after intramuscular injection. Part I: tissue residue depletion.

Heavy sows (n = 126) were treated with penicillin G procaine at a 5× label dose (33 000 IU/kg) for 3 consecutive days by intramuscular (IM) injection using three patterns of drug administration. Treatments differed by injection pattern and injection volume. Sets of sows were slaughtered 5, 10, 15, 20, 25, 32, and 39 days after the last treatment; skeletal muscle, kidney, serum, and urine were collected for penicillin G analysis by LC-MS/MS. Penicillin G at withdrawal day 5 averaged 23.5 ± 10.5 and 3762 ± 1932 ng/g in muscle and kidney, respectively. After 15 days of withdrawal, muscle penicillin G residues were quantifiable in only one treated hog (3.4 ng/g) but averaged 119 ± 199 ng/g in kidneys. Using a hypothetical tolerance of 50 ng/g and a natural log-linear depletion model, the withdrawal period required for penicillin depletion to 50 ng/g was 11 days for skeletal muscle and 47 days for kidney.

Tissue deposition and residue depletion of melamine in fattening pigs following oral administration

The adulteration of animal feed as well as milk products with melamine has led to concerns about the ability to establish appropriate withdrawal intervals to ensure food safety. Two experiments were conducted in this study. The first was to investigate the deposition and depletion of melamine in blood and tissues of pigs exposed to adulterated feed with high doses of melamine. A total of 500 or 1000 mg kg–1 melamine was added to the diet for fattening pigs (initial BW = ±60.24 kg). Melamine residues were detected in tissues (brain, duodenum, liver, heart, muscle and kidney) by LC-MS/MS. Dose-dependent effects were found between melamine residual concentration and its dose in feed. Five days after the withdrawal of melamine from the diets, the residue concentration in tissues fell below 2.5 mg kg–1. In the second experiment, blood samples were taken at different time points from fattening pigs (BW = 100 kg) fed with adulterated feed with 1000 mg kg–1 of melamine for 42 days. Results from the pharmacokinetics analysis showed that it would take 83 h for the melamine level in plasma depleting to the safe level of 50 ng ml–1 after an expose of 1000 mg kg–1 melamine contaminated feed for 42 days.