LIPOSOMES AND NIOSOMES AS TOPICAL DRUG CARRIERS - DERMAL AND TRANSDERMAL DRUG-DELIVERY

A critical analysis of (trans)dermal delivery of substances encapsulat ed within liposomes and liposomes is presented. Topical liposomes or n iosomes may serve as solubilization matrix, as a local depot for susta ined release of dermally active compounds, as penetration enhancers, o r as rate-limiting membrane barrier for the modulation of systemic abs orption of drugs. The mechanism(s) of vesicle-skin interaction and dru g delivery are being extensively investigated using radioactive- or fl uorescence-labeled marker molecules and drugs, and various electron an d (laser) light microscopic visualization techniques, and different mo dels describing the interaction with and fate of vesicles in the skin have been proposed. With the current experimental data base on hand, m ost investigators agree that direct contact between vesicles and skin is essential for efficient delivery, although phospholipids per se app arently do not penetrate into deeper skin layers. Investigators have m ostly focused on dermal corticosteroid liposome products. However, loc alized effects of liposome-associated proteins such as superoxide dism utase, tissue growth factors and interferons appear also to be enhance d. The delivery of liposome-encapsulated proteins and enzymes into dee per skin layers has been reported, although the mechanism of delivery remains to be elucidated. An objective assessment of the performance o f topical liposome formulations vs. conventional dosage forms is frequ ently obscured by investigators comparing equal concentrations, rather than equivalent thermodynamic activities of their respective formulat ions. We conclude that liposomes and niosomes may become a useful dosa ge form for a variety of dermally active compounds, specifically due t o their ability to modulate drug transfer and serve as nontoxic penetr ation enhancers.