Long-term Stability of a Compounded Suspension of Torsemide (5 mg/mL) for Oral Administration

Torsemide use for congestive heart failure (CHF) has been reported, but prescription frequency is unknown. Commercially available tablet sizes in North America limit dosing precision, indicating a need to evaluate its strength and stability in suspension.

To determine the frequency of torsemide prescriptions and to determine a beyond use date (BUD) of a compounded suspension of torsemide for oral administration stored under 2 temperature conditions for 90 days.

No animals used.

Pharmacy records were retrospectively reviewed for torsemide and furosemide prescriptions from 2008 to 2015 at 2 veterinary referral centers. After preliminary strength testing, compounded torsemide suspension (5 mg/mL) for oral administration was prepared using torsemide tablets suspended in OraPlus:OraSweet 1:1, buffered to a pH of 8.3 and stored at refrigeration (2-8°C) and room temperature (20-25°C) in 2 oz amber plastic bottles. Samples were analyzed by reverse phase high-performance liquid chromatography (RP-HPLC) on days 0, 14, 30, 60, and 90.

Prescriptions for torsemide increased from 2008 to 2015. Analysis of the torsemide 5 mg/mL suspension for oral administration at each time point met United States Pharmacopeia (USP) requirements for torsemide content of 90-110% of label claim. The average strength at 90 days decreased to 92 ± 3% at 2-8°C and 95 ± 2% at 20-25°C. Stability testing did not detect unknown impurities.

Increasing torsemide use warrants availability of a validated and stable compounded formulation. Our results support the assignment of a 90-day BUD for torsemide 5 mg/mL suspension for oral administration compounded in OraPlus:Sweet 1:1 buffered to a pH of 8.3.