Stability of Compounded Digoxin Solution 0.05 mg/mL for Injection

Background: In 2015, commercial pediatric digoxin injection 0.05 mg/mL was discontinued, leaving only one adult concentration (0.25 mg/mL) for injection on the Canadian market. No published studies have documented the chemical stability over a long period of time of a diluted solution of digoxin for injection. Objective: The aim of this study was to assess the chemical stability of 2 digoxin injection formulations 0.05 mg/mL diluted in 2 vehicles stored at 5°C or a 25°C. Methods: The compounded solution of digoxin 0.05 mg/mL for injection was prepared with digoxin 0.25 mg/mL after dilution in 2 different vehicles, normal saline, and a compounding of the commercial vehicle. Half of the compounding products were stored in 2 mL transparent glass vials at 25°C and the other half at 5°C. Chemical stability was evaluated by HPLC-UV analysis on days 0, 14, 30, 60, 90, 120, 150, 180 for each temperature conditions. In addition, samples were tested for organoleptic change, presence of particular matter as well as sterility. Results: For all tested preparations, the concentration of digoxin remained above 90.0% of the initial concentration throughout the 180-day study. Furthermore, no organoleptic change was observed; particulate matter assessment was in acceptable range; and sterility specifications were met. Conclusions: Digoxin 0.05 mg/mL obtained with a dilution of digoxin 0.25 mg/mL by normal saline or a copy of the commercial vehicle remained stable for at least 180 days at 5°C and 25°C.