Stability Evaluation of Minoxidil in FOAMIL Foam Base with Bracketing Study Design

Topical minoxidil is a common medication prescribed for treating hair loss-related problems. Currently a wide range of minoxidil concentrations (2% to 15%) have been prescribed for the topical treatment of hair loss, but the majority of minoxidil solutions contain potential skin irritating inactive ingredients such as propylene glycol and high amounts of alcohol that may cause undesirable side effects. In order to minimize these side effects, FOAMIL, a propylene glycol-free and alcohol-reduced foam vehicle, was developed to compound minoxidil solutions of varying dosages. Since long-term use of this drug is necessary to maintain the clinical results, the objective of this study was to conduct a 180-day bracketed validated stability-indicating study of four compounded minoxidil solutions (2%, 5.5%, 6%, 15%) in FOAMIL. The samples were prepared by mixing the minoxidil with an appropriate amount of FOAMIL without any heating or filtration process. The obtained preparations were packaged into 100-mL foamer bottles before sending out for physicochemical analyses at pre-determined time points (days; 0, 30, 60, 90, 120, 150, and 180) and antimicrobial effectiveness testing to thirdparty independent analytical laboratories. Our results showed that the strength of all minoxidil solutions remained within the United States Pharmacopeia specification (90% to 110%) for 180 days. There were no significant changes in pH measurements and physical stability (color, odor, precipitation). Antimicrobial effectiveness of the preservative system also met the United States Pharmacopeia requirements at the end of the 180-day stability study for all concentrations. Based on the U.S. Food and Drug Administration's guidance on bracketed study design, the findings of this study show that any concentration of minoxidil at or between 2% to 5.5% and 6% to 15% in FOAMIL can be considered stable for at least 180 days when stored at ambient condition.