Formulation design and evaluation of a transdermal drug delivery system containing a novel eptazocine salt with the Eudragit® E adhesive

Abstract

We aimed to select an appropriate permeation enhancer for the percutaneous absorption of eptazocine (EPZ) and develop a prolonged-release EPZ transdermal patch using Franz diffusion cells fitted with hairless mouse skin. We tested several enhancers and found that the effect on the skin permeation of EPZ of an isopropyl myristate (IPM) solution system was improved by adding glyceryl monocaprylate (GEFA-C8). The patches had a film former (Eudragit® E) as the matrix backbone, with 10% free EPZ, 10% IPM, and 5% GEFA-C8. The addition of 5% citric acid to the Eudragit E matrix led to a three-fold increase in the flux of EPZ (31.4 μg/cm2/h). Changing the form of EPZ loaded onto the patch from the free form to a salt form (hydroxybromide [HBr], hydrochloride, lactate, oxalate, citrate, and tartrate), with concentrations of 20% EPZ, led to drug retention in the matrix without crystallization. The patches with 20% EPZ HBr salt, 10% IPM, and 5% GEFA-C8 exhibited the highest permeation flux (48.3 μg/cm2/h). These results indicate that EPZ HBr salt in a Eudragit® E matrix could be used as a novel analgesic transdermal drug delivery system.