Acta Pharm. 50 (2000) 265-271

Original scientific paper  

Accelerated stability test of a new co-trimoxazole (trimethoprim-sulfamethoxazole mixture) injection formulation


1Industrial Pharmacy Research Laboratory Labs., Tehran University of Medical Sciences, Tehran,
P.O. Box 14395-459, Iran
2LACDR, Leiden University, Leiden, The Netherlands
Received January 25, 2000      Accepted October 16, 2000

A new formulation of co-trimoxazole injection has been prepared and its stability has been investigated by reversed-phase high-perfomance liquid chromatography. A commercially available brand of co-trimoxazole ampoule was included in the study for comparison. The new formulation contained trimethoprim (TMP) and sulfamethoxazole (SMX) in the ratio of 1:5 (m/m) in polyethylene glycol 400/ propylene glycol mixture. Sodium formaldehyde sulfoxylate was used as antioxidant and sodium hydroxide was utilized for adjusting the pH. The preparation was sterilized by ultrafiltration and then added into presterilized ampoules. No discernible physical changes of prepared formulations due to crystallization of TMP and SMX have been observed after preparation and storage under normal conditions (25 C). Shelf-life of the proposed as well as brand formulations was determined using the accelerated stability test of Arrhenius. It has been demonstrated that the decomposition of both injectable fluids obeys first-order kinetics. The result of the study suggests that, taking into account the standard error and its effect on calculating the rate constant and expiration date, the room temperature shelf-life of fabricated and brand samples are 822 and 909 days, respectively.

Keywords: co-trimoxazole, trimethoprim, sulfamethoazole, injection, stability