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

Abstract

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.

Keywords: calves; extralabel withdrawal interval; pneumatic dart administration; remote drug delivery; tissue residue depletion; tulathromycin.

Figure 1.

Estimated withdrawal intervals (days) for tulathromycin in calves after administering 2.6 mg/kg tulathromycin via pneumatic dart administration based on the EMA (European Medicines Agency) method using WT 1.4 software based on the calculated CP-60,300 concentration data. MRL: maximum residue limits for CP-60,300 expressed as tulathromycin equivalents from the EMA (EMA, 2015a). If the calculated withdrawal interval was a fraction of a day, the estimated withdrawal interval was rounded up to the next day shown in the parenthesis. Note that the calculated withdrawal interval for the injection site showed a value of “-1” in the WT 1.4 interface, suggesting that the value was out of the typical calculation range. The value of >135 (136) was obtained by visual inspection of the produced figure.

Figure 2.

Estimated withdrawal intervals (days) for tulathromycin in calves after administering 2.6 mg/kg tulathromycin via pneumatic dart administration using the U.S. FDA method (coded in the “reschem” R package) based on the calculated CP-60,300 concentration data. The tolerance of 5.5 ppm (5,500 µg/kg) for CP-60,300 in the liver is from 21CFR556.745. FDA does not have tolerance levels for CP-60,300 in kidney, muscle, or fat. Therefore, the maximum residue limits (MRLs) for CP-60,300 in the kidney, muscle, and fat from the EMA (EMA, 2015a) were used in the calculation. If the calculated withdrawal interval was a fraction of a day, the estimated withdrawal interval was rounded up to the next day. The withdrawal interval for the injection site muscle was also calculated by setting the tolerance to be 10-fold of the tolerance for non-injection site muscle (FDA, 2018), but the value was out of the calculation range and the “reschem” program showed an error, so the result is not shown here.

Figure 3.

Estimated withdrawal intervals (days) for tulathromycin in calves after administering 2.6 mg/kg tulathromycin via pneumatic dart administration using the U.S. FDA method (coded in the “reschem” R package) based on the measured tulathromycin concentration data. In the United States, the marker residue of tulathromycin is CP-60,300 and the tolerance is 5.5 ppm (5,500 µg/kg) for CP-60,300 in the liver, but there is no information on the tolerance for tulathromycin in any other edible tissues in the United States. Therefore, the maximum residue limits (MRLs) for CP-60,300 in the kidney, muscle, and fat from the European Medicines Agency (EMA, 2015a) were used in the calculation. If the calculated withdrawal interval was a fraction of a day, the estimated withdrawal interval was rounded up to the next day. The withdrawal interval for the injection site muscle was also calculated by setting the tolerance to be 10-fold of the tolerance for non-injection site muscle (FDA, 2018), but the value was out of the calculation range and the “reschem” program showed an error, so the result is not shown here.