Combination effect of penetration enhancers and propylene glycol on in vitro transdermal absorption of insulin.

In vitro transdermal absorption of insulin was improved when the penetration enhancers Azone, N-methyl-2-pyrrolidone (NMP) or dimethyl sulfoxide (DMSO) were incorporated in propylene glycol (PG) formulations of the drug. Maximum penetration efficacy depended on optimal concentrations of both the enhancer and PG. Azone and NMP showed maximum efficacy at 0.1% and 12.0% concentration, respectively. In both cases, the optimum concentration of PG was 40.0%. The enhancing ability of DMSO was much lower in comparison with the other two enhancers.