Time-course and accumulation of triclabendazole and its metabolites in bile, liver tissues and flukes collected from treated sheep

• Only the TCBZ sulpho-metabolites were recovered in plasma from TCBZ treated sheep.
• These metabolites were also the main analytes accumulated within adult flukes.
• TCBZ was the main compound accumulated in liver tissue from TCBZ treated sheep.
• The hydroxy-metabolite was recovered in bile from treated sheep.
• Oral ingestion seems to be the main route of drug entry into the flukes.

The flukicidal compound triclabendazole (TCBZ) has a complex metabolic pattern that includes the systemic presence of its sulphoxide (TCBZ.SO) and sulphone (TCBZ.SO2) metabolites, usually recovered from the bile of treated animals. The aim of the current work was to evaluate the time-course and pattern of in vivo accumulation of TCBZ/metabolites into adult Fasciola hepatica specimens recovered from infected sheep. Twelve (12) healthy Corriedale sheep were orally infected with one hundred (100) metacercariae of the TCBZ-susceptible Cullomptom isolate of F. hepatica. Sixteen weeks after infection, animals were intraruminally treated with TCBZ (10 mg/kg). At 3, 24, 48 and 60 h post-treatment (pt), animals were sacrificed (n = 3/time period) and samples of blood, bile, liver tissue and adult F. hepatica specimens were collected. The concentrations of TCBZ/metabolites were measured by HPLC. TCBZ.SO and TCBZ.SO2 were the only molecules recovered in the bloodstream, with peak plasma concentrations of 10.8 μg/mL (TCBZ.SO) and 12.6 μg/mL (TCBZ.SO2). The same metabolites were also the main analytes accumulated within the adult flukes, reaching peak concentrations between 6.35 μg/g (TCBZ.SO) and 13.9 μg/g (TCBZ.SO2) at 24 h pt, which was coincident with the time when the maximum plasma concentration was attained. Low levels of TCBZ parent drug (0.14 μg/g at 24 h pt) were measured within collected flukes. TCBZ parent drug and its sulpho- and hydroxy-derivatives were recovered in bile collected from treated sheep between 3 and 60 h pt. Although relatively high concentrations of hydroxy-TCBZ (ranging from 0.86 to 10.1 μg/mL) were measured in bile, this metabolite was not recovered within the flukes at any time pt. Finally, TCBZ parent drug was the main compound accumulated in liver tissue over the 60 h pt period. The time-course and drug concentration patterns within the adult liver fluke after TCBZ treatment followed a similar trend to those observed in plasma. Overall, the data reported here confirm that oral ingestion is a main route of drug entry into the trematode in vivo exposed to TCBZ/metabolites. However, the presence of TCBZ within the adult fluke (despite being absent in the systemic circulation) may be related to some degree of trans-tegumental diffusion from bile or by a direct oral ingestion from portal blood.

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