Efficacy of oxyclozanide against adult Paramphistomum leydeni in naturally infected sheep

The aim of the current study was to assess oxyclozanide (OCZ) efficacy against Paramphistomum leydeni in naturally infected adult sheep. OCZ concentrations in blood stream and gastrointestinal fluids collected from treated animals were also measured. Fifteen P. leydeni naturally infected sheep were randomly divided into two groups: untreated control (n=5) and treated (n=10). The treated group was orally drenched with OCZ (20mg/kg, day 0). A second dose was administered 72h later. Faecal samples were taken at days 0, +3 and +5. Five sheep from both groups were slaughtered at day +5. At necropsies, rumen, abomasum and small intestine were examined for adult and immature flukes. All recovered flukes were counted and the treatment efficacy was estimated. Additionally, serum and gastrointestinal fluid content (ruminal, abomasal and small intestine) samples, obtained from five treated animals at day +5, were analyzed by HPLC to measure OCZ concentrations. OCZ showed high efficacy (99%) against mature P. leydeni. The post-treatment egg reduction was also high after the first dose with values ranging from 98.4% (day +3) to 99.5% (day +5). The highest OCZ concentrations were measured in serum (20.7±11.5μg/mL) followed by the small intestinal fluid (6.00±4.50μg/mL). Very low OCZ concentrations (ranging between 0.05 and 0.02μg/mL) were measured in ruminal and abomasal fluids. OCZ administered to sheep twice (20mg/kg) by the oral route was highly efficacious against mature stages of P. leydeni in naturally infected sheep. Despite a high drug concentration at the intestinal fluid, OCZ efficacy against immature stages could not be assessed. OCZ efficacy and assessment of its concentration profiles in different tissues are considered a contribution to the scarce information available on this ruminant fluke.