Penetration enhancing effects of selected natural oils utilized in topical dosage forms

Context: Various natural products, including oils, have been utilized as penetration enhancers due to their "safety profiles". These oils contain fatty acids promoting skin permeability through lipid fluidization within the stratum corneum; and might therefore be able to effectively enhance transdermal drug delivery. Objective: We investigated possible penetration enhancing properties of selected oils, utilizing flurbiprofen as marker compound in emulgel formulations. The formulations were compared to a liquid paraffin emulgel and a hydrogel to establish any significant penetration enhancing effects. Methods: Gas chromatographic analysis of the natural oils was performed at ambient temperature to determine the fatty acid composition in each selected natural oils. Franz cell diffusion studies and tape stripping methods were employed to study delivery of the marker into, and through the skin. Results: The following rank order for the emulgel flux-values was obtained: Hydrogel >>> olive oil >> liquid paraffin >> coconut oil > grape seed oil >> Avocado oil ≥ Crocodile oil >> Emu oil. Discussion: Results suggested that oils containing predominantly mono-unsaturated oleic acid, on average increased the flux of the marker to a larger extent than oils containing an almost even mixture of both mono- and poly-unsaturated fatty acids. Oils comprising saturated fatty acids (SFAs) with alkyl chains between C 12 and C 14 , increased the marker flux to a higher extent than oils containing C 16 -C 18 SFAs. Effects observed for branched fatty acids, however, did not vary significantly from effects for unbranched fatty acids with the same carbon chain length. Conclusion: Natural oils possess penetration enhancing effects.