Cimetidine increases serum mebendazole concentrations. Implications for treatment of hepatic hydatid cysts.

In eight patients (five with peptic ulcer disease and three with hydatid cysts), the [14C]-aminopyrine breath test (ABT) and maximum serum concentration of mebendazole following a dose of 1.5 g of mebendazole three times daily were determined before and after treatment with cimetidine (400 mg three times daily for 30 days). Serum mebendazole concentrations were measured in blood samples taken 2 h after each drug intake. Cimetidine lowered the 14CO2 specific activity (SA) at 1 h (P less than 0.01) and increased the maximum serum concentration of mebendazole (P less than 0.01). A significant correlation was found between SA at 1 h and the highest concentration of mebendazole before (r = -0.71, P less than 0.05) and after (r = -0.82, P less than 0.05) cimetidine ingestion. Combined administration of cimetidine and mebendazole resulted in the complete resolution of previously unresponsive hydatid cysts.