Assessment of the inhibitory potency of benzydamine on albendazole hepatic metabolism in sheep

Abstract

Albendazole (ABZ), a benzimidazole methylcarbamate anthelmintic compound, is still widely used to control helminth infections in all animal species and man. The hepatic ABZ S-oxidation by both flavin-monooxygenase (FMO) and cytochrome P450 systems (Virkel et al., 2004; Souhaili El Amri et al., 1988), accounts for a considerable reduction on its pharmacologic activity. Thus, interference with the oxidative metabolism may enhance the systemic exposure of active drug/metabolites improving its anthelmintic efficacy. Focussed in the search for new potential pharmacologic strategies to inhibit ABZ metabolism, this research assessed the effects of the FMO substrate benzydamine (BZ) on the hepatic S-oxidation of this anthelmintic in sheep. The effects of BZ were compared to those produced by methimazole (MTZ), a well known FMO inhibitor of ABZ metabolism. MATERIALS AND METHODS Liver microsomes were obtained from adult Corriedale rams (n=4) following the methodology described by Virkel et al. (2004). MTZ S-oxidation (FMO-dependent specific activity) (Dixit & Roche, 1984) was assayed in the absence/presence of BZ (750 μM). ABZ S-oxidation was assessed by the amount of ABZ-sulphoxide (ABZSO) formed. The substrate (100 µM) was incubated (15 min at 37ºC) either in the absence or in the presence of variable concentrations (12.5 to 1000 μM) of either BZ or MTZ. Samples were analyzed by HPLC. Statistical comparisons were performed using the Student t-test. RESULTS In pooled sheep liver microsomal fractions the Clint of the specific FMO-dependent enzyme activity (MTZ S-oxidation) was lower in the presence of BZ (53 vs. 95 µL/min.mg). ABZ was metabolized to its (-) and (+) ABZ-sulphoxide (ABZSO) enantiomers. Both BZ and MTZ inhibited ABZ S-oxidation. The estimated IC50?s for both inhibitors are shown in Table 1. DISCUSSION BZ inhibited the hepatic FMO-dependent specific enzyme activity in sheep. Both BZ and MTZ showed a stronger inhibitory potency over the (+)ABZSO production, which is believed to be catalyzed by FMO in sheep. Although the inhibitory potency of BZ was lower compared to MTZ, a clinically relevant metabolic interaction after the concomitant administration of two different drugs may occur if adequate concentrations are achieved at the site of biotransformation at the same time. Thus, further studies aimed to evaluate this metabolic interaction in vivo are required to determine BZ potential to increase ABZ systemic exposure and efficacy in sheep.