Effects of transdermal penetration enhancers on the permeability of shed snakeskin

Chemical penetration enhancers: a patent review

BACKGROUND

Ever since transdermal drug delivery came into existence, it has offered great promises, although most of them are yet to be fulfilled owing to some intrinsic restrictions of the transdermal route. On the positive side, transdermal drug delivery systems present advantages including non-invasiveness, prolonged therapeutic effect, reduced side effects, improved bioavailability, better patient compliance and easy termination of drug therapy. The greatest hindrance in the percutaneous delivery is the obstruction property of the stratum corneum, the outermost layer of the skin, in addition to usual problems such as skin binding, skin metabolism, cutaneous toxicity and prolonged lag times.

OBJECTIVE

This paper reviews investigations on the feasibility and application of penetration enhancers as described in recent patents, which help in the selection of a suitable sorption promoter(s) for enhanced delivery of medicaments through the skin.

METHOD

The patents granted under various categories of penetration enhancers have been discussed including fatty acids, terpenes, fatty alcohol, pyrrolidone, sulfoxides, laurocapram, surface active agents, amides, amines, lecithin, polyols, quaternary ammonium compounds, silicones, alkanoates and so on.

CONCLUSION

Scores of promising chemicals have been harnessed for their skin permeation promoting capacity as mentioned earlier. In future, many more chemicals and putative enhancers are likely be documented and patented.

Effects of ionization and penetration enhancers on the transdermal delivery of 5-fluorouracil through excised human stratum corneum

The purpose of this study was to determine the effects of ionization and penetration enhancers on the transdermal delivery of 5-fluorouracil (5-FU) through excised human stratum corneum. The in vitro transport of 5-FU was determined at three physiologically relevant pH values of 5.0, 7.4 and 8.0, and in the presence of suitable penetration enhancers, namely Azone (AZ), lauryl alcohol (LA), and isopropyl myristate (IPM). The results showed that passive permeation of 5-FU is dependent upon the pH of the donor solution, although did not fully conform to the pH-partition hypothesis. A further analysis of data suggested an inverse relationship (i.e., negative correlation) between steady-state flux and aqueous solubility of 5-FU at these pH values (correlation coefficient = -0.4205), although correlation was not statistically significant (p = 0.7237). In the absence of a penetration enhancer, the in vitro permeability of 5-FU was quite low (0.82+/-0.06 x 10(4) cm/h). This delivery rate was enhanced by approximately by 3, 4 and 24-fold, respectively, when IPM, LA, and AZ were incorporated into the donor solution. All these enhancements were statistically significant (p < 0.05) compared to control, and occurred regardless of the polarity (solubility parameters) of these enhancers. Out of three examined enhancers, AZ appears to be a suitable enhancer for enhancing transport of 5-FU, which merits in vivo investigation in a suitable animal model. Possible mechanisms of enhancement by these penetration enhancers are also discussed.

Effect of bilayer distruption on transdermal transport of low-molecular weight hydrophobic solutes

PURPOSE

Applications of transdermal drug delivery are limited by low skin permeability. Several chemicals have been used to enhance transdermal drug transport, many of which enhance skin permeability by disordering lipid bilayers. The objective of this study was to develop a mathematical model to describe the effect of bilayer disrupting agents on skin permeability to low molecular weight hydrophobic drugs.

METHODS

I predicted solute partition and diffusion coefficients in the lipid bilayers of the stratum corneum using scaled particle theory, which calculates these coefficients based on the work required to create a cavity to incorporate the solute in the lipid bilayer.

RESULTS

Model equations predicted that no significant permeability enhancement would be observed for small solutes (MW < 100). Thereafter, the enhancement, E, increases with solute cross-sectional area. The resulting equation to predict the enhancement of skin permeability is given by E = exp[alpha(r2 - 8.7)], where r is solute molecular radius in angstroms and alpha is the degree of bilayer disorder. Predictions of the model were compared with the experimental data collected from several studies.

CONCLUSIONS

The model predictions compare well with the experimental data.

Permeation enhancers for transdermal drug delivery

The transdermal route has been recognized as one of the highly potential routes of systemic drug delivery and provides the advantage of avoidance of the first-pass effect, ease of use and withdrawal (in case of side effects), and better patient compliance. However, the major limitation of this route is the difficulty of permeation of drug through the skin. Studies have been carried out to find safe and suitable permeation enhancers to promote the percutaneous absorption of a number of drugs. The present review includes the classification of permeation enhancers and their mechanism of action; thus, it will help in the selection of a suitable enhancer(s) for improving the transdermal permeation of poorly absorbed drugs.