Extemporaneous Topical Minoxidil Solutions for the Treatment of Alopecia: Stability Studies and Incorporation Tests of Active Ingredients in ALOPLUS FAST Base.

Minoxidil is a vasodilator drug generally employed for the treatment of various forms of alopecia. In this article, the authors propose an alternative to the formulation reported in the British Pharmacopoeia for the realization of topical minoxidil -based solutions using ALOPLUS FAST. This liquid vehicle is an ethanol- and propylene glycol-free base which allows the complete solubilization of minoxidil, thanks to the presence of hydroxypropyl-ß-cyclodextrin. Solubility and chemical stability studies of the active ingredient in the formulation at a concentration of 5% w/w and physical stability studies of this extemporaneous preparation are reported. Incorporation tests of various active pharmaceutical ingredients that can be combined with minoxidil for alopecia synergic treatment have been carried out. Analyses were performed by using a high-pressure liquid chromatography analytical method. The results showed that the intrinsic solubility of the drug in the liquid base was 62.37 mg/mL ± 0.85 mg/mL (5.24 w/w ± 0.07% w/w) at 25°C; minoxidil was chemically stable in ALOPLUS FAST; and the formulation was physically stable for more than six months, under different storage conditions. Incorporation tests of several active pharmaceutical ingredients in 2% to 4% w/w minoxidil formulations were successful as well.