Toltrazuril sulfone (Ponazuril) residue depletion in pig tissues and estimated withdrawal intervals

Ponazuril (Marquis®) is a triazine based antiprotozoal medication labeled to treat equine protozoal myeloencephalitis in the United States. Ponazuril is often used in an extra-label manner to treat coccidiosis in piglets, but tissue residue data is limited. In this study, piglets were given a single oral dose of 5 mg/kg ponazuril. Piglets (n = 5) were euthanized at eleven timepoints (0, 15, 28, 43, 57, 71, 85, 99, 113, 127, and 141 days) with tissue sample collection and chromatographic analysis. The maximum residue limit (MRL) values established by the European Medicines Agency (EMA) and our laboratory limits of detection (LOD) were used as the safe levels to estimate withdrawal intervals (WDIs). Based on MRL values, the WDIs for liver, kidney, muscle and fat were approximately 72 days, 176 days, 90 days and 81 days, respectively. As this is extra-label use, any residue detected will be a violation. If the LOD was used instead of the MRL values, the WDIs would extend to as much as 130 days (liver), 270 days (kidney), 105 days (muscle), and 101 days (fat).