Influence of nanosized delivery systems with benzyl nicotinate and penetration enhancers on skin oxygenation

Many novel nanosized delivery systems have been designed for topical application of drugs since they can overcome the skin barrier and improve drug bioavailability. The increased absorption is often a consequence of a reversibly disrupted barrier function of the skin by the vehicle itself or by specific ingredients that act as penetration enhancers. This paper reports the effects of two nanosized systems (microemulsion and liposomes), in the presence and absence of penetration enhancers (PE), on the topical delivery of a lipophilic drug in vivo and compares that to classical hydrogel formulation. A vasodilator benzyl nicotinate (BN), which increases the blood flow of the skin, was incorporated into the formulations, and skin oxygenation was followed by electron paramagnetic resonance oximetry. It was found that microemulsions and liposomes (with or without PE) accelerate the rate of BN action when compared to hydrogel. However, incorporation of PE in microemulsion also improves the effectiveness of BN action. To understand why PE enhances the action of BN, its effect on the structure of the stratum corneum was investigated in vitro. The increased fluidity of the stratum corneum lipids provides an explanation for the greater penetration of BN into the skin when the drug and PE are together incorporated into the appropriate formulation.