Physical, chemical, and microbiological stability of extemporaneous furosemide suspensions

Background: Furosemide is a potent diuretic used in treatment of oedematous states associated with cardiac, renal, and hepatic failure and the treatment of hypertension. In Thailand, no liquid formulation of furosemide is commercially available for pediatric administration and for adult who cannot swallow furosemide tablets.

Objective: Prepare extemporaneous furosemide suspensions from commercial furosemide tablets using two compounded suspending vehicles, and determine the physical, chemical, and microbiological stability of these preparations.

Methods: Two formulations of extemporaneous furosemide suspensions were prepared from commercially available furosemide 40-mg tablets using two compounded suspending vehicles. The final concentration of furosemide in each formulation was 2 mg/mL. Three samples of each formulation were stored in glass bottles protected from light, and kept at three controlled temperature, 4±2°C, room temperature (30±2°C), and 45°C. A sample was removed from each bottle immediately after preparation and at 7, 14, 30, 45, and 60 days. The stability-indicating highperformance liquid chromatography was used to analyze for furosemide. The pH was measured. The physical and microbiological properties of these formulations were evaluated after storage for two months. The stability of furosemide suspensions was determined by calculating the percentage of the initial concentration remaining on each test day. Stability was defined as retention of at least 90% of the initial concentration.

Results: At least 93% of the initial furosemide concentration remained in both compounded furosemide suspensions for up to 60 days. There were no substantial changes in the appearance (color and consistency) or odor of both formulations. The pH values of both formulations kept at 4±2°C increased slightly, while the pH values of both formulations kept at 45±2°C decreased significantly compared with the initial pH value of both formulations. Both formulations maintained microbiologic stability for 60 days.

Conclusion: Extemporaneously compounded furosemide suspensions, 2 mg/mL, were stable for at least 60 days when stored in glass bottles protected from light at three controlled temperatures. These compounded furosemide suspensions are better suited for administration to children and adults who cannot swallow furosemide tablets. They may provide an alternative in situations where the marketed suspension is unavailable.