Development of Stable and Simple Finasteride 333-μg/mL Suspensions that Minimize Occupational Exposure

Finasteride is not commercially available in a liquid format, which stimulated the development of a stable and simple finasteride suspension formulation. The objectives of this work were to develop and test a finasteride suspension for 1) simplicity to compound, 2) pharmaceutical acceptability, 3) stability, and 4) potential for occupational exposure. The stability of commercial 5-mg finasteride tablets (50 mg/150 mL) was evaluated in water, Oral Mix, and OralMix SF in amber polyethylene terephthalate bottles at 25°C or 4°C. Additional stability studies were carried out using sugar-free Finasteride Powder USP in amber polyethylene terephthalate bottles and tablets in water in polypropylene oral syringes. On study days 0, 1, 3, 7, 14, 28, 38, 49, 63, and 90, the finasteride concentration was determined using a validated stability-indicating liquid chromatographic method. The potential occupational airborne exposure was evaluated by attempting to measure finasteride in 1000 liters of room air following shaking and nebulization. Finasteride suspension/dispersion formulations were prepared in water, Oral Mix, and Oral Mix SF from tablets and pure powder. All formulations retained more than 94.3% of the initial finasteride concentration, with 95% confidence, when stored for up to 90 days at room temperature or 4°C. Simulations of occupational exposure failed to demonstrate the presence of finasteride in room air following attempts to nebulize finasteride mixtures. We conclude that 333-µg/mL suspension/dispersions of finasteride in water or Oral Mix products will have more than 94.3% of the initial finasteride concentration remaining after 90 days, regardless of the formulation, container, or storage temperature. Although we could not detect finasteride in room air, given the analytical limits of the study, we estimate that exposure would unlikely exceed 3.6-µg/1000 liters of room air. Nevertheless, since current regulations are based on "no safe limit," use of primary engineering controls and personal protective equipment as appropriate is recommended.