Glyceryl monocaprylate/caprate as a moderate skin penetration enhancer

Eleven widely used lipophilic formulation excipients have been screened for their skin penetration enhancing effects. The excipients tested were glyceryl tricaprylate/caprate, isopropyl myristate, glyceryl monocaprylate/caprate, decyl oleate, polyethylene glycol-6 glyceryl dicaprylate/caprate, isopropyl isostearate, isostearyl isostearate, glyceryl monoisostearate, polyglyceryl-3 diisostearate, vegetable squalane and isostearyl alcohol. Excipient effects were evaluated by measuring skin permeability coefficients towards a model hydrophilic drug, 5-fluorouracil (5-FU), before and after a 6-h treatment with neat excipient. The skin penetration enhancing mixture, 10% (w/w) Azone(R) in propylene glycol, was used as a positive control. Only one excipient, glyceryl monocaprylate/caprate, had enhancement effects significantly above the buffer control (p<0.05). This excipient increased 5-FU penetration 10-fold. log P-octanol/water and hydrophilic-lipophilic balance values were calculated for each of the excipients. It was concluded that, of the excipients screened, glyceryl monocaprylate/caprate is the only penetration enhancer because (1) it is the least lipophilic, (2) it has surfactant properties, and (3) it has the optimum alkyl chain length for surfactant-type skin penetration enhancers. Since glyceryl monocaprylate/caprate has only moderate enhancement effects, it should be useful as a mild, well-tolerated skin penetration enhancer. (C) 1998 Elsevier Science B.V. All rights reserved.