Biochemical effects of fenbensazole on Hymenolepis diminuta in vivo

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An investigation of the chemotherapeutic and biochemical effects of a new broad-spectrum anthelmintic, fenbendazole, (FBZ, methyl 5-[phenylthio]-benzimadazole-2-carbamate), on Hymenolepis diminuta in experimentally infected rats is reported. FBZ proved to be highly active against H. diminuta; a single oral dose of 12.5, 25 and 50 mg/kg body wt. on day 15 of infection eliminated 77, 100 and 88% of the tapeworms respectively as determined at necropsy 24 h after treatment. The chemotherapeutic actions of FBZ on H. diminuta in vivo were accompanied by marked changes in worm wt. and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of FBZ 18 h earlier were significantly smaller and contained much less glycogen (as a percent of the fresh wt.) than worms from unmedicated controls. Protein concentrations rose in FBZ-treated worms, but more slowly than the rate of decline in glycogen concentration. Glycogen/protein ratios in FBZ-treated worms were considerably lower than the corresponding control values. Differences in the absolute amounts of glycogen and protein between control and drug-treated worms were even more profound. Administration of a single oral dose of FBZ (14 mg/kg) to the rat produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm wt. and chemical composition. In vitro studies, carried out 16 h after treatment, revealed that FBZ-treated worms absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability to the worm to accumulate glucose against a concentration difference was significantly depressed.