Metformin stability and shelf life
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Metformin Stability and Shelf Life: Key Factors
Shelf Life of Metformin Formulations
Studies show that the shelf life of metformin products can vary depending on the formulation and brand. For example, a novel pulsatile delivery system of metformin hydrochloride demonstrated a shelf life of approximately 1.94 years under stability testing conditions, indicating good stability for this specific formulation . In a comparison of local brands in Pakistan, some metformin tablet brands achieved a shelf life of up to 3 years, while others did not meet this standard, highlighting variability among products .
Impact of Storage Temperature on Metformin Stability
Temperature plays a significant role in the stability and shelf life of metformin. Bile acid-based microcapsules containing metformin showed that higher storage temperatures (above 25°C) can alter the physical properties and drug release profiles, potentially reducing shelf life and stability. In contrast, storage at lower temperatures (below 0°C) had negligible effects on the capsules' morphology and drug content . This suggests that metformin formulations are best stored at controlled, cooler temperatures to maintain stability.
In-Use Stability and NDMA Impurity Concerns
Recent research has raised concerns about the formation of N-nitrosodimethylamine (NDMA), a carcinogenic impurity, in metformin products during storage and use. Studies found that both immediate-release and extended-release metformin products can develop NDMA levels above the acceptable daily intake (ADI) limit, especially after being stored at 30°C/75% relative humidity for several weeks. The NDMA content increased significantly during in-use stability testing, indicating that storage conditions can directly impact the safety and shelf life of metformin products 46. This issue has led to recalls of several metformin products and highlights the importance of monitoring impurity levels during storage.
Stability in Biological Samples for Therapeutic Drug Monitoring
For therapeutic drug monitoring, metformin hydrochloride in plasma is stable for up to 6 hours at room temperature (25°C) and up to 30 days at 4°C. However, in plasma samples, stability at room temperature is limited to 6 hours, and at -20°C, stability is maintained for only 1 day. These findings are important for ensuring accurate measurement of metformin levels in clinical settings .
Conclusion
Metformin's stability and shelf life depend on formulation type, storage temperature, and exposure to environmental conditions. While some formulations can remain stable for up to three years, improper storage—especially at higher temperatures—can reduce shelf life and increase the risk of harmful impurities like NDMA. Regular quality checks and proper storage are essential to ensure the safety and effectiveness of metformin products 123456.
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