Development of an oral formulation of azetirelin, a new thyrotropin-releasing hormone (TRH) analogue, using n-lauryl-beta-D-maltopyranoside as an absorption enhancer.

Abstract

The effects of formulation factors on the enhancement of colonic absorption of azetirelin by n-lauryl-beta-maltopyranoside (LM) were studied in rats. Coadministration of LM with a small volume of azetirelin solution to the proximal colon increased the AUC of the drug by 8.7-fold. There were no significant differences in the LM-induced absorption profiles of azetirelin between unligated and ligated colon. The addition of a viscous polymer to the drug solution, which delayed the in vitro release of both azetirelin and LM, reduced the promoting effects of LM. These results suggest that the action of LM is not affected by sample spreading in the colonic lumen, whereas a rapid release of both azetirelin and LM from the formulation is necessary to maximize the efficacy of LM. Utilizing the balloon sonde method, the effects of LM were also confirmed in the colonic loop of dogs. Based on these results, an enteric capsule formulation of azetirelin containing LM and citric acid (CA), a potential inhibitor of the bacterial degradation of azetirelin in the distal intestine, was prepared and its performance was evaluated in fasted dogs. The bioavailability of azetirelin after the oral administration of this enteric capsule with LM and CA was 43.5% compared with a bioavailability of 14.9% in capsules without LM and CA. Therefore, the delivery of azetirelin and LM to the lower intestine, together with a rapid release of capsule contents, are feasible for the improved peroral bioavailability of azetirelin.