Serum pharmacokinetics and tissue and milk residues of oxytetracycline in goats following a single intramuscular injection of a long-acting preparation and milk residues following a single subcutaneous injection

A Preliminary Study on the Concentration of Oxytetracycline and 4-Epi-Oxytetracycline in Sow Milk

Even though modern analytical chemistry has developed a methodology enabling evaluation of the presence of OTC in milk, data regarding its concentration in the material collected from lactating sows are missing. Therefore, this paper was intended to provide new data on the transmission of OTC and its epimer, 4-epi-oxytetracycline (4-epi-OTC), in the milk of lactating sows after a singular intramuscular administration of a long-acting form of the antibiotic. The determination of OTC and 4-epi-OTC was carried out using ultrahigh-performance liquid chromatography with mass spectrometry (UHPLC–MS/MS). The highest average concentration of antibiotic (1132.2 µgL⁻¹) was observed in samples collected 1 day after the administration of the drug. The average OTC level at day 3 was 358 µgL⁻¹. The average concentration of the antibiotic found on the 21st day was 12.3 µgL⁻¹. The highest average concentration of 4-epi-OTC—i.e., 54 µgL⁻¹—was noted 1 day after the administration. Amongst samples collected at day 3, the average level of the substance in question was 26.4 µgL⁻¹. The average value observed at day 21 was 1.5 µgL⁻¹. Our results indicated considerable OTC and 4-epi-OTC transmission into the milk of lactating sows.

Development and Application of an interactive Physiologically Based Pharmacokinetic (iPBPK) Model to Predict Oxytetracycline Tissue Distribution and Withdrawal Intervals in Market-Age Sheep and Goats

Oxytetracycline (OTC) is a widely used antibiotic in food-producing animals. Extralabel use of OTC is common and may lead to violative residues in edible tissues. It is important to have a quantitative tool to predict scientifically-based withdrawal intervals (WDIs) after extralabel use in food animals to ensure human food safety. This study focuses on developing a physiologically based pharmacokinetic (PBPK) model for OTC in sheep and goats. The model included seven compartments: plasma, lung, liver, kidneys, muscle, fat, and rest of the body. The model was calibrated with serum and tissue (liver, muscle, kidney, and fat) concentration data following a single intramuscular (IM, 20 mg/kg) and/or intravenous (IV, 10 mg/kg) administration of a long-acting formulation in sheep and goats. The model was evaluated with independent datasets from Food Animal Residue Avoidance Databank (FARAD). Results showed that the model adequately simulated the calibration datasets with an overall estimated coefficient of determination (R2) of 0.95 and 0.92, respectively, for sheep and goat models and had acceptable accuracy for the validation datasets. Monte Carlo sampling technique was applied to predict the time needed for drug concentrations in edible tissues to fall below tolerances for the 99th percentiles of the population. The model was converted to a web-based interactive PBPK (iPBPK) interface to facilitate model applications. This iPBPK model provides a useful tool to estimate WDIs for OTC after extralabel use in small ruminants to ensure food safety and serves as a basis for extrapolation to other tetracycline drugs and other food animals.

Pharmacokinetics of Conventional and Long-Acting Oxytetracycline Preparations in Kilis Goat

The pharmacokinetics of conventional and long-acting (LA) oxytetracycline (OTC), widely used broad-spectrum antibacterial drugs in veterinary medicine, were evaluated in Kilis goats at single dosage of 20 mg/kg body weight (bw). A total of 21 goats were divided into three groups: intravenous (Group I) and intramuscular (IM) (Group II) administration of the conventional formulation and IM administration of the LA formulation (Group III). Blood samples were taken at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, 60, 72, and 96 h; and OTC analysis was performed by HPLC. For Group III and Group II, time to reach maximal plasma drug concentration (T_max) was 0.6 ± 0.28 and 0.46 ± 0.09 h and maximal plasma drug concentrations (C_max) were 8.72 ± 2.47 μg/ml and 13.57 ± 5.83 μg/ml, respectively. In Group I, C₀ concentration was found to be 63.51 ± 11.59 μg/ml. The elimination times (T_1/2) were 10.84 ± 3.20, 27.96 ± 11.66, and 10.47 ± 1.30 h; and AUC were 115 ± 29.12, 96.44 ± 9.49, and 80.86 ± 12.76 μg/ml/h for Group I; Group II, and Group III, respectively. Bioavailability by IM administration were 69.71% for the conventional OTC and 83.15% for the LA OTC.

Applicability of Screening Tests for Oxytetracycline in the Milk of Three Breeds of Goats

Antibiotics are widely used in animal husbandry, and the presence of antibiotic residues in milk is a health hazard. The objectives of this study were to determine residual amounts of oxytetracycline in the milk of three breeds of goats using high-pressure liquid chromatography (HPLC) analysis and screening tests. It was also essential to explore the safe withdrawal period of oxytetracycline in lactating goats and examine the applicability of Charm ROSA and SNAP screening tests. The qualitative results of these tests were compared with the quantitative results of the HPLC method. Fifteen milking does, five each from the Alpine, LaMancha, and Nubian breeds, were selected from the herd at Prairie View A&M University. Milk samples containing antibiotic residues were deproteinized by HCl and acetonitrile, and then oxytetracycline was extracted from the supernatant. The residues of oxytetracycline in goat's milk up to 110 h after injection were qualitatively detected using the Charm ROSA test. Similarly, the SNAP test detected the antibiotic residues in milk up to 110 h after treatment. The HPLC results indicated that oxytetracycline residues in milk from Alpine goats were below the tolerance level (300 ng/ml) 82 h after drug treatment (72 h for LaManchas, 58 h for Nubians); however, the results of the screening tests would indicate longer withdrawal periods for milk from the breeds of goats studied, which would result in economic losses to goat's milk producers. The results of this study also indicated that oxytetracycline was not stable in raw goat's milk at refrigeration temperature or during pasteurization and that the concentrations decreased significantly. Commercial goat's milk is usually exposed to several hours of refrigeration and then to pasteurization. The results of this study indicated that, if oxytetracycline was present in raw goat's milk, the concentration would decrease significantly before it was marketed.

Validation of an Analytical Methodology for Determination of Oxytetracycline Residue in Milk by HPLC with UV Detection

ABSTRACT Oxytetracycline (OTC) is used for the prophylaxis and treatment of a great number of diseases since this antibiotic possesses broad-spectrum activity against many pathogenic organisms. The use of OTC has become a serious problem because of the possible existence of its residues in milk, which can be directly toxic or cause allergic reactions in some hypersensitive individuals. Even low-level doses of antibiotic in milk consumed for long periods can lead to problems regarding the spread of drug-resistant microorganisms. The purpose of the present study was to investigate residual OTC in consuming milk in Tehran using high-performance liquid chromatography (HPLC) with UV detector. OTC residues in extracts obtained from a preliminary cleanup procedure and recoveries from spiked OTC in desire concentrations were between 80% and 97% with appropriate coefficients of variation. The limit of detection (LOD) and limit of determination (LOQ) were 50 and 68.5 ng/mL, respectively. This result shows that this method would be useful for routine monitoring of oxytetracycline residues in bovine dairy milk.

Determination of oxytetracycline levels in rainbow trout serum on a biphenyl column using high-performance liquid chromatography

We developed a simple and sensitive high-performance liquid chromatography method on a biphenyl column to determine oxytetracycline (OTC) levels in rainbow trout serum. The assay used deproteination, filtration, and subsequent separation on a reverse-phase biphenyl column, with UV detection at 355 nm. OTC (7.8-7.9 min) was completely resolved from structurally similar riboflavin (10.4-10.5 min), a common feed supplement. Estimated limits of detection and quantitation of OTC were 0.01 and 0.04 microg/mL, respectively. The average recovery for OTC was 102% with a R.S.D. of 8.34%. Calibration standards were linear from 0.01 to 10 microg/mL.

Volumes of distribution

Volumes of distribution are proportionality constants between total amount of drug in the body and plasma concentrations. As snapshot plasma drug concentrations may be measured in different conditions (at equilibrium, under pseudo-equilibrium condition,...), several volumes of distribution have been defined. The two most relevant are the volume of distribution at equilibrium (V(ss)), and the volume of distribution during pseudo-equilibrium (V(area)). Volumes of distribution are used to compute a loading dose (V(ss)) or the residual amount of drug in the body knowing plasma concentrations (V(area)). Volume of distribution may be interpreted in terms of drug distribution having recourse to physiological models involving drug binding to plasma and tissues. Volumes of distribution should be determined early in drug development programmes and those having a large volume of distribution may be selected to obtain a long terminal half-life even for drugs having a relatively high clearance.