Stability of Extemporaneously Compounded Suspensions of Trimethoprim and Sulfamethoxazole in Amber Plastic Bottles and Amber Plastic Syringes.

Abstract

Trimethoprim (TMP) and sulfamethoxazole (SMX) are widely used, in combination, to treat or prevent various infections. Unfortunately, no liquid oral formulation is currently available in Canada for patients who are unable to swallow tablets. To evaluate the stability of suspensions of TMP and SMX (8 and 40 mg/mL, respectively) prepared in Oral Mix or Oral Mix SF vehicle (Medisca Pharmaceutique Inc) and stored for up to 90 days in amber plastic bottles or amber plastic syringes at 5°C or 25°C. Suspensions were prepared from bulk powder and from tablets in Oral Mix and Oral Mix SF vehicles, then transferred to amber plastic (polyethylene terephthalate glycol) bottles and plastic oral syringes and stored at 5°C and 25°C. Samples were collected on predetermined study days (0, 7, 14, 23, 45, 60, 75, and 90 days) and analyzed using a validated high-performance liquid chromatography - ultraviolet detection method. A suspension was considered stable if it maintained at least 90% of its initial concentration with 95% confidence. Observations of organoleptic characteristics such as colour and odour, as well as pH, were used to assess physical stability. Suspensions prepared from bulk powder maintained concentrations of TMP and SMX of at least 97% of the initial concentration over the 90-day study period. No obvious changes in colour, odour, or pH were observed. However, acceptable suspensions could not be prepared from the commercial tablets. A persistent foam that developed at the surface of all suspensions prepared from tablets could result in inconsistent dosing. Extemporaneously compounded oral suspensions of TMP and SMX (8 and 40 mg/mL, respectively) prepared from bulk powder in Oral Mix and Oral Mix SF vehicles and stored in amber plastic bottles or syringes at 5°C or 25°C remained stable for at least 90 days. Suspensions made from tablets produced unacceptable formulations.