Long-term stability of trimix: a three-drug injection used to treat erectile dysfunction

A three-drug injection mixture of alprostadil 12.5 microgram/mL, papaverine hydrochloride 4.5 mg/mL and phentolamine mesylate 0.125 mg/mL in bacteriostatic 0.9% sodium chloride injection was evaluated for stability at 23 deg C, 4 deg C, -20 deg C and -70 deg C. The injection remained clear and colorless in all samples throughout the study. Chemical stability testing was performed using stability-indicating high-performance liquid chromatographic analysis. Alprostadil was the least stable of the drug components at room temperature and under refrigeration. About 8% alprostadil loss occurred in five days at room temperature; under refrigeration losses of about 6% and 11% occurred after 1 and 2 months, respectively. Frozen at -20 deg C and -70 deg C, less than 5% loss of any of the drug componenets occurred in 6 months. A beyond-use date of 6 months when stored frozen at -20 deg C and 1 month when stored refrigerated at 4 deg C is appropriate for batches of the injection that have passed sterility testing. Room temperature exposure should be limited, and the vial should be returned to refrigeration as soon as possible.