Albendazole-praziquantel interaction in healthy volunteers: kinetic disposition, metabolism and enantioselectivity

center dot Pharmacokinetic interactions between albendazole and praziquantel are based on plasma concentrations of the enantiomeric mixture of both drugs with contradictory data, although the antiparasitic activity arises from (-)-(R)-praziquantel and (+)-albendazole sulfoxide. WHAT THIS STUDY ADDS center dot The pharmacokinetic interaction between albendazole and praziquantel is enantioselective. Praziquantel increased the plasma concentrations of (+)-albendazole sulfoxide more than those of (-)-albendazole sulfoxide and the administration of albendazole did not change the kinetic disposition of (+)-(S)-praziquantel, but increased the plasma concentration of (-)-(R)-praziquantel. AIM This study investigated the kinetic disposition, metabolism and enantioselectivity of albendazole (ABZ) and praziquantel (PZQ) administered alone and in combination to healthy volunteers. METHODS A randomized crossover study was carried out in three phases (n = 9), in which some volunteers started in phase 1 (400 mg ABZ), others in phase 2 (1500 mg PZQ), and the remaining volunteers in phase 3 (400 mg ABZ + 1500 mg PZQ). Serial blood samples were collected from 0-48 h after drug administration. Pharmacokinetic parameters were calculated using a monocompartmental model with lag time and were analyzed using the Wilcoxon test; P < 0.05. RESULTS The administration of PZQ increased the plasma concentrations of (+)-ASOX (albendazole sulphoxide) by 264% (AUC 0.99 vs. 2.59 mu g ml-1 h), (-)-ASOX by 358% (0.14 vs. 0.50 mu g ml-1 h) and albendazole sulfone (ASON) by 187% (0.17 vs. 0.32 mu g ml-1 h). The administration of ABZ did not change the kinetic disposition of (+)-(S)-PZQ (-)-(R)-4-OHPZQ or (+)-(S)-4-OHPZQ, but increased the plasma concentration of (-)-(R)-PZQ by 64.77% (AUC 0.52 vs. 0.86 mu g ml-1 h). CONCLUSIONS The pharmacokinetic interaction between ABZ and PZQ in healthy volunteers was demonstrated by the observation of increased plasma concentrations of ASON, both ASOX enantiomers and (-)-(R)-PZQ. Clinically, the combination of ABZ and PZQ may improve the therapeutic efficacy as a consequence of higher concentration of both active drugs. On the other hand, the magnitude of this elevation may represent an increased risk of side effects, requiring, certainly, reduction of the dosage. However, further studies are necessary to evaluate the efficacy and safety of this combination.