Patchouli oil microemulsion-in-gel system for topical treatment of psoriasis

Psoriasis is a common chronic recurrent inflammatory skin disease that can hardly be cured by current treatments. Patchouli oil (PAO) is an essential oil with anti-inflammatory activity, with the potential for treatment of psoriasis. However, due to its unstable and oily properties, the development of PAO formulations remains challenging. In this work, a microemulsion-in-gel (MEG) of PAO was developed to enhance transcutaneous delivery and treat psoriasis. The formulation was characterized by the dual functions of PAO serving as both the active pharmaceutical ingredient and the oil phase. The thus-prepared microemulsion (ME) benefited from high PAO content (up to 10%, w/w) and the elimination of the use of external carrier oils. This optimized ME was subsequently incorporated into a hydrogel matrix to formulate the MEG. In vitro results showed that PAO MEG effectively improved the stability of PAO, and enhanced the transcutaneous retention of patchouli alcohol and pogostone. In vivo studies using an imiquimod (IMQ)-induced psoriasis mouse model demonstrated that PAO-MEG effectively ameliorated skin lesions, reduced PASI scores, mitigated body weight loss, decreased spleen index, and attenuated epidermal thickness, indicating substantial therapeutic efficacy. This developed PAO microemulsion-in-gel represents a promising topical delivery system that enhances both the stability and transcutaneous efficiency of PAO, offering a novel therapeutic strategy for psoriasis management.