Expiration Date of Extemporaneous Pyrimethamine Formulations for Treating Congenital Toxoplasmosis: Physicochemical and Microbiological Evaluation.

This study evaluated the stability of extemporaneous pyrimethamine oral suspensions prepared from commercial tablets using 85% sucrose or 70% sorbitol as vehicles. A validated HPLC method was employed to quantify pyrimethamine and assess its chemical stability. Physicochemical parameters including macroscopic appearance, pH, particle size, and drug content were monitored for 90 days at 5 and 25 °C. Both formulations maintained acceptable pH values and pyrimethamine content within pharmacopeial limits. Particle size increased over time, likely due to aggregation, while appearance remained unchanged for up to 45 days. Microbiological assessments showed that microorganisms remained within acceptable limits, with no objectionable microorganisms detected. Overall, both suspensions demonstrated chemical and microbiological stability for up to 45 days (Suspension S) and 60 days (Suspension X) under both storage conditions. These results support the preparation of cost-effective pyrimethamine formulations for treating congenital toxoplasmosis in pediatric patients.