Effect of combinations of marketed human anthelmintic drugs against Trichuris muris in vitro and in vivo

BACKGROUND: Soil-transmitted helminth (STH) infections are responsible for a huge public health burden, however treatment options are limited. The discovery and development of novel efficacious drugs or drug combinations for the treatment of STH infections therefore has a high research priority. METHODS: We studied drug combination effects using the main standard anthelmintics, albendazole, mebendazole, levamisole, pyrantel pamoate and ivermectin in the Trichuris muris model. Drug combinations were first tested in vitro and additive and synergistic combinations investigated further in vivo in female mice using ratios based on the ED(50) of the respective drugs. RESULTS: In vitro all 10 combinations of the standard anthelmintics tested against T. muris revealed synergistic behavior. We identified three drug combinations in vivo as strongly synergistic, namely mebendazole-ivermectin (Combination index (CI)=0.16), mebendazole-levamisole (CI=0.17) and albendazole-mebendazole (CI=0.23). For albendazole-ivermectin, moderate synergism was observed (CI=0.81) and for albendazole-levamisole a nearly additive effect was documented (CI=0.93) in vivo. Five combinations (albendazole-pyrantel pamoate, mebendazole-pyrantel pamoate, levamisole-pyrantel pamoate, levamisole-ivermectin and pyrantel pamoate-ivermectin) were antagonistic in vivo. CONCLUSION: Our results strengthen the evidence that combination chemotherapy might play a role in the treatment of Trichuris infections. Albendazole-mebendazole should be studied in greater detail in preclinical studies.