Preformulation studies of finasteride to design matrix systems for topical delivery

A preformulation study with finasteride (FIN) was conducted to enable the development of a topical matrix system to treat androgenic alopecia. The compatibility of the drug with hidroxypropyl-β-cyclodextrin (HPβCD) and the hydrophilic polymers Klucel EXF (KLU) and Soluplus (SOL) were evaluated according to a simplex centroid mixture design. An extensive analytical arsenal was used to encompass the stability of the drug in the different mixtures. The selected excipients showed to have intense thermal interaction with FIN, which was dependent on the composition of the sample, shifting FIN melting peak to reduced temperatures along with the decrease of its associated enthalpy. The mixture design allowed measuring the interactions between components, showing that KLU enhanced the ability of the drug to form inclusion complexes with HPβCD, while SOL exhibited the opposite effect. The stability of samples was preserved even after a thermal treatment used to simulate pharmaceutical processing. Indeed, no drug content decaying was observed, which corroborates the chemical stability of the systems as indicated by thermogravimetry, chromatographic, morphological and spectroscopic assays. The original crystalline phase of the drug (orthorhombic form I) did not change after the heating treatment of the samples, demonstrating its physical stability. Thus, these series of experiments may guide the development of delivery systems for topical use of FIN, showing which combinations and proportions of components can lead to better results in terms of stability and drug delivery.