Topical delivery of doxepin using liposome containing cream: An emerging approach in enhancing skin retention

Conventional formulation of topical doxepin has similar antihistaminic effects as oral doxepin; however, its efficacy is limited due to poor localized effects on the skin. This study was designed to compare the ex vivo permeation and retention of two topical doxepin formulations; liposomal cream and plain cream. Doxepin-containing liposomes were prepared with the thin-film hydration method and assessed for size, size distribution, morphology, entrapment efficiency (EE%) and stability Using rat skin specimens in a Franz diffusion cell. Doxepin concentration in skin and receptor fluid was quantified by a validated HPLC method. The optimized liposomal formulation represented a uniform shape with narrow size distribution and an average diameter of 208.7±5.6nm. EE% of doxepin was 79±1.3 and the liposomes were stable at least for six weeks at 4^°C. Ex vivo studies showed that while a significantly higher amount of doxepin has passed through the skin and entered the receptor compartment from conventional dosage form (47.06±2.5µg/cm2vs 11.20±0.6µg/cm2 for liposomal formulation), liposomal doxepin favoured accumulation in dermis and epidermis. These results suggest that the liposomal doxepin cream is an effective and easy-to-use formulation and may improve the cutaneous retention of doxepin, thus decreasing its systemic side effects.