AUTHOR=Carreño Gútiez Marta , Mercer Melissa A. , Martínez-López Beatriz , Griffith Ronald W. , Wetzlich Scott , Tell Lisa A. 

TITLE=Estimation of withdrawal interval recommendations following administration of fenbendazole medicated feed to ring-necked pheasants (Phasianus colchicus)

JOURNAL=Frontiers in Veterinary Science

VOLUME=Volume 11 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1444009

DOI=10.3389/fvets.2024.1444009

ISSN=2297-1769

ABSTRACT=Prescribing fenbendazole medicated feed for pheasants in the USA is considered extra-label drug use, and the Animal Medicinal Drug Use Clarification Act requires that a safe estimated withdrawal interval (WDI) be applied following administration to this minor food-producing species. This study sought to determine the pharmacokinetic and residue depletion profile for fenbendazole and its major metabolites in pheasants' (n=32) liver and muscle tissue samples in order to estimate a WDI for pheasants following fenbendazole administration as an oral medicated feed at 100 ppm for 7 consecutive days. Fenbendazole, fenbendazole sulfoxide, and fenbendazole sulfone in pheasant liver and muscle samples were analyzed using HPLC-UV. Liver and muscle sample concentrations were used to estimate WDIs using FDA, European Medicines Agency (EMA), and half-life multiplication methods with US poultry tolerances, EMA maximum residue limits, and the analytical limit of detection (LOD; 0.004 ppm) as the residue limits. Terminal elimination half-lives were estimated by noncompartmental analysis using a naïve pooled data approach and were 14.4 h for liver, 13.2 h for thigh muscle, and 14.1 h for pectoral muscle. The maximum estimated withdrawal interval was 153 h (7 days) for fenbendazole sulfone for pectoral muscle using the FDA tolerance method (95 % confidence interval for the 99 th percentile of the population), and the LOD as the residue limit.