Stability Evaluation of Minoxidil in Foam Base with Bracketing Study Design

Three years ago, a study was conducted to evaluate the stability of four different concentrations of minoxidil (2%, 5.5%, 6%, 15%) in FOAMIL, a propylene glycol-free and alcohol-reduced foam vehicle, over a period of 180 days. The minoxidil solutions were prepared by mixing the drug with FOAMIL and packaged into 100-mL foamer bottles. Physicochemical analyses and antimicrobial effectiveness testing were performed at predetermined time points. The results showed that all minoxidil solutions remained within the United States Pharmacopeia specification (90% to 110%) for 180 days, with no significant changes in pH measurements and physical stability. The antimicrobial effectiveness of the preservative system also met the United States Pharmacopeia requirements at the end of the study. Therefore, any concentration of minoxidil 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.