Enhancing effect of terpenes on the in vitro percutaneous absorption of diclofenac sodium.

The enhancing effect of naturally occurring terpenes on the in vitro percutaneous absorption of diclofenac sodium (DFS) from carbopol gels containing propylene glycol was investigated. Permeation experiments were performed on excised abdominal rat skin. Terpenes varied in their activities: the alcohol terpenes were effective accelerants for the drug whereas the ketones were much less efficient, providing only a 2-to-3-fold increase in DFS diffusion; limonene showed mild accelerant activity and 1,8-cineole was a poor accelerant. Acyclic alcohols were found to be the best enhancers for DFS, being geraniol, with an almost 20-fold increase, the most outstanding penetration enhancer. However, although the addition of terpenes increased DFS flux, diffusional lag times were longer than for the control gel.