Effect of dose increase or cimetidine co-administration on albendazole bioavailability

The low bioavailability of albendazole affects the therapeutic response in patients with echinococcosis. Cimetidine co-administration is reported to improve bioavailability. To analyze the assumed dose-dependent bioavailability of albendazole, we administered 5 to 30 mg/kg albendazole to 6 male volunteers in a randomized cross-over study. To assess the effect of cimetidine (10 mg/kg twice daily), the drug was given with albendazole (20 mg/kg). A dose-dependent bioavailability was not observed. This was due to inter-individual variability of the maximal concentration (Cmax 38%-72%) of albendazole sulphoxide (ABZSX), the active metabolite of albendazole. Cmax was 0.21+/-0.14 mg/L after 5 mg/kg and 0.39+/-0.19 mg/L after 30 mg/kg albendazole (P = 0.217). Cimetidine tended to decrease Cmax by 52% (P = 0.109) and significantly inhibited ABZSX breakdown as indicated by the prolongation of ABZSX elimination half-life from 7.4+/-3.3 hr to 19.0+/-11.7 hr (P = 0.028). Remarkably, the inter-individual variability of Cmax was significantly lower during cimetidine co-administration: 14% versus 72%.