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

To 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, 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 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 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.