Safety studies evaluating the effect of mebendazole on liver function in dogs

The effect of repeated and exaggerated mebendazole administration was evaluated in dogs with and without experimentally induced altered liver function. Irish Setters and Toy Poodles were dosed at 1, 3, and 5 times the therapeutic dose (22 mg/kg) of mebendazole for 17 days, without any effect on the liver. Mixed breed dogs that received increasing doses of mebendazole at 11 to 110 times the therapeutic dose for 2 months did not show adverse effects and remained in good health throughout the experiment. There was not substantial evidence that carbon tetrachloride-induced liver changes were exacerbated by subsequent repeated treatments with mebendazole at 15 times the therapeutic dose. Additionally, in dogs whose liver function was compromised experimentally by glutathione depletion and microsomal enzyme induction, administration of mebendazole at this same dosage for 30 days did not result in any hepatotoxic effect. When mebendazole was given at 15 times the therapeutic dose prior to an hypoxic episode in dogs pretreated with a barbiturate and high protein diet, there was no evidence of any adverse effect on liver function. These metabolic manipulations, in conjunction with mebendazole administration, failed to reveal any mechanism of hepatic dysfunction associated with mebendazole treatment. Unrecognized factors appear to be involved with the rare cases of hepatic dysfunction that have been reported after mebendazole administration. Only careful documentation of field cases and further laboratory research can identify these factors.