Formulation of Erythromycin and Tretinoin in a topical gel base

Acne vulgaris is a chronic and prevalent usually self-limited disorder. Topical medication is the main route for acne therapy. In this disorder the most widely used topical preparations are antibiotics such as Erythromycin and keratolytic agents such as Tretinoin. Excellent results with minimal side effects may be achieved by a fixed combination of Tretinoin and Erythromycin. This combination therapy increases efficacy and a faster response in the treatment of acne may be achieved. The purpose of this work was to assess a suitable formulation of Erythromycin and Tretinoin in a topical gel base. UV spectrophotometer analysis was chosen for Erythromycin and Tretinoin assay. This method was adapted to assay Erythromycin and Tretinoin in their combination. The proposed method for Erythromycin was the formation of a complex with O-nitrobenzaldehyde, in glacial acetic acid and in the presence of hydrochloric acid, which manifested maximum absorbance at 486 nm. For the measurement of Tretinoin, the absorption peak at 355 nm in acidic ethanol-water-isopropyl alcohol (IPA) mixture was suitable. In order to formulate the Erythromycin and Tretinoin in a gel base, gelling agents, plasticizers, solvents, cosolvents such as carbopol, HPC, HPMC, ethanol, propylene glycol (PG), isopropyl alcohol (IPA) and water have been used. By using tertiary diagrams, the most proportionate percentage of gel constituents have been determined. The formulations have been controlled for rheological, organoleptic properties and physical and chemical stability under several conditions (4, 25, 40°C). The release of drugs from the gels was studied using Franz diffusion cell and the best formulations were chosen. Drug release rates followed Higuchi’s law. The results indicated that Erythromycin and Tretinoin could be formulated in a gel base with a suitable release profile and presented to pharmaceutical market.