In vivo and in vitro sensitivity of Fasciola hepatica to combinations of triclabendazole and artesunate, artemether or OZ78

Triclabendazole resistance is continually documented from livestock and hence new treatment strategies for F. hepatica infections are needed. We investigated the effect of combinations with triclabendazole and artesunate, artemether or OZ78 compared to monotherapy against adult and juvenile F. hepatica in rats. In vitro experiments with triclabendazole and its sulfoxide and sulfone metabolites, each in combination with the peroxides complemented our study. F. hepatica infected rats were subjected to single drugs or drug combinations 3-4 weeks (juvenile flukes) and <8 weeks (adult flukes) post infection. Negative binomial regressions of worm and egg counts were used to analyze dose-response relationships and whether effects of drug combinations were synergistic or antagonistic. The in vitro assays were evaluated by means of viability scales based on fluke motility. ED50 values of 113, 78, 23 and 2.7 mg/kg were calculated for monotherapy with artesunate, artemether, OZ78 and triclabendazole, respectively against adult F. hepatica. Likelihood ratio tests revealed synergistic interactions (p>0.05) of combinations of triclabendazole (2.5 mg/kg) plus artesunate or artemether on adult worm burden. Antagonistic effects on the adult burden and egg output were observed when a lower triclabendazole dose (1.25 mg/kg) was combined with the artemisinins. No significant interactions (p=0.07) were observed for OZ78 and triclabendazole combinations and between the triclabendazole effect and the effects of the other partner drugs on juvenile worms. Our in vitro studies of adult worms agreed with the in vivo results, while in vitro analysis of juvenile worms revealed greater interactions than observed in vivo. In conclusion, single agent triclabendazole demonstrated a more potent in vivo and in vitro fasciocidal activity than the experimental drugs artesunate, artemether and OZ78. When combined, synergistic but also antagonistic effects depending on the doses administered were observed, which should be elucidated in more detail in future studies