Pharmacokinetics of tulathromycin in plasma and milk samples after a single subcutaneous injection in lactating goats (Capra hircus )

Pharmacokinetics of Tildipirosin in Plasma, Milk, and Somatic Cells Following Intravenous, Intramuscular, and Subcutaneous Administration in Dairy Goats

Tildipirosin is a macrolide currently authorized for treating respiratory diseases in cattle and swine. The disposition kinetics of tildipirosin in plasma, milk, and somatic cells were investigated in dairy goats. Tildipirosin was administered at a single dose of 2 mg/kg by intravenous (IV) and 4 mg/kg by intramuscular (IM) and subcutaneous (SC) routes. Concentrations of tildipirosin were determined by an HPLC method with UV detection. Pharmacokinetic parameters were estimated by non-compartmental analysis. Muscle damage, cardiotoxicity, and inflammation were evaluated. After IV administration, the apparent volume of distribution in the steady state was 7.2 L/kg and clearance 0.64 L/h/kg. Plasma and milk half-lives were 6.2 and 58.3 h, respectively, indicating nine times longer persistence of tildipirosin in milk than in plasma. Moreover, if somatic cells are considered, persistence and exposure measured by the area under concentration–time curve (AUC) significantly exceeded those obtained in plasma. Similarly, longer half-lives in whole milk and somatic cells compared to plasma were observed after IM and SC administration. No adverse effects were observed. In brief, tildipirosin should be reserved for cases where other suitable antibiotics have been unsuccessful, discarding milk production of treated animals for at least 45 days or treating goats at the dry-off period.

Effects of experimentally induced respiratory disease on the pharmacokinetics and tissue residues of tulathromycin in meat goats

Tulathromycin is a macrolide antibiotic commonly used for the treatment of respiratory disease in food animal species including goats. Recent research in pigs has suggested that the presence of disease could alter the pharmacokinetics of tulathromycin in animals with respiratory disease. The objectives of this study were (a) compare the plasma pharmacokinetics of tulathromycin in healthy goats as well as goats with an induced respiratory disease; and (b) to compare the tissue residue concentrations of tulathromycin marker in both groups. For this trial, disease was induced with Pasteurella multocida. Following disease induction, tulathromycin was administered. Samples of plasma were collected at various time points up to 312 hr posttreatment, when study animals were euthanized and tissue samples were collected. For PK parameters in plasma, V_z (control: 28.7 ± 11.9 ml/kg; experimental: 57.8 ± 26.6 ml/kg) was significantly higher (p = 0.0454) in the experimental group than the control group, and nonsignificant differences were noted in other parameters. Among time points significantly lower plasma concentrations were noted in the experimental group at 168 hr (p = 0.023), 216 hr (p = 0.036), 264 hr (p = 0.0017), 288 hr (p = 0.0433), and 312 hr (p = 0.0486). None of the goats had tissue residues above the US bovine limit of 5 µg/g at the end of the study. No differences were observed between muscle, liver, or fat concentrations. A significantly lower concentration (p = 0.0095) was noted in the kidneys of experimental goats when compared to the control group. These results suggest that the effect of respiratory disease on the pharmacokinetics and tissue residues appear minimal after experimental P. multocida infection, however as evidenced by the disparity in C_max , significant differences in plasma concentrations at terminal time points, as well as the differences in kidney concentrations, there is the potential for alterations in diseased versus clinical animals.

Estimation of tulathromycin depletion in plasma and milk after subcutaneous injection in lactating goats using a nonlinear mixed-effects pharmacokinetic modeling approach

BACKGROUND

Extra-label use of tulathromycin in lactating goats is common and may cause violative residues in milk. The objective of this study was to develop a nonlinear mixed-effects pharmacokinetic (NLME-PK) model to estimate tulathromycin depletion in plasma and milk of lactating goats. Eight lactating goats received two subcutaneous injections of 2.5 mg/kg tulathromycin 7 days apart; blood and milk samples were analyzed for concentrations of tulathromycin and the common fragment of tulathromycin (i.e., the marker residue CP-60,300), respectively, using liquid chromatography mass spectrometry. Based on these new data and related literature data, a NLME-PK compartmental model with first-order absorption and elimination was used to model plasma concentrations and cumulative excreted amount in milk. Monte Carlo simulations with 100 replicates were performed to predict the time when the upper limit of the 95% confidence interval of milk concentrations was below the tolerance.

RESULTS

All animals were healthy throughout the study with normal appetite and milk production levels, and with mild-moderate injection-site reactions that diminished by the end of the study. The measured data showed that milk concentrations of the marker residue of tulathromycin were below the limit of detection (LOD = 1.8 ng/ml) 39 days after the second injection. A 2-compartment model with milk as an excretory compartment best described tulathromycin plasma and CP-60,300 milk pharmacokinetic data. The model-predicted data correlated with the measured data very well. The NLME-PK model estimated that tulathromycin plasma concentrations were below LOD (1.2 ng/ml) 43 days after a single injection, and 62 days after the second injection with a 95% confidence. These estimated times are much longer than the current meat withdrawal time recommendation of 18 days for tulathromycin in non-lactating cattle.

CONCLUSIONS

The results suggest that twice subcutaneous injections of 2.5 mg/kg tulathromycin are a clinically safe extra-label alternative approach for treating pulmonary infections in lactating goats, but a prolonged withdrawal time of at least 39 days after the second injection should be considered to prevent violative residues in milk and any dairy goat being used for meat should have an extended meat withdrawal time.

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.