Enhancement of bioavailability by lowering of fat content in topical formulations

The cosmetic properties of topical formulations are important parameters for the adherence to treatment, where modern oil-in-water emulsions are considered more acceptable compared with ointments. After application of an emulsion to the skin, the concentration of active ingredients in the formulation residue on the skin will increase, due to evaporation of volatile ingredients. The aim of the present study was to investigate the effect of changes in vehicle fatty content on the skin penetration of two active ingredients: benzyl nicotinate (BN) and betamethasone valerate (BV). Formulations containing 0.5% BN and 0.3% BV in vehicles with different lipid content (10-80%) were applied in a randomized and double-blind manner to the forearm of healthy volunteers. The changes in skin colour (erythema and blanching) were then monitored visually and with a new noninvasive instrument. The BN formulation containing 10% fat induced erythema more rapidly and with higher intensity than the formulations with higher fat content. Increased efficacy was also observed from the low-fat content formulation of BV, which gave more blanching than the formulations with high fat content. The rate of penetration of the active ingredients was inversely related to the lipid content, i.e. simple changes of the cosmetic properties by modifications of the lipid content may affect the efficacy of a formulation.