The shelf life of a drug preparation is the amount of time that the product can be stored before it becomes unfit for use, through either chemical decomposition or physical deterioration.
- Storage temperature affects shelf life. It is generally understood to be ambient temperature unless special storage conditions are specified.
- In general, a preparation is considered fit for use if it varies from the nominal concentration or dose by no more than 10%, provided that the decomposition products are not more toxic or harmful than the original material.
Shelf life testing aids in determining the standard shelf life of a formulation.
Samples are stored at accelerated, long term and at room temperature. The samples are then analyzed at various intervals to determine the rate of decomposition. Shelf life is calculated from this rate.
Because storage time at these temperatures can result in an extended testing time, accelerated testing is conducted as well, with a range of higher temperatures. The rate constants obtained from these samples are used to predict shelf life at ambient or refrigeration temperatures.
Accelerated stability testing is not useful if temperature changes are accompanied by changes in the reaction mechanism or by physical changes in the system (e.g., change from the solid to the liquid phase).
Stability at room temperature can be predicted by Arrhenius equation -
On the other hand ''Decision Tree for Data Evaluation for Retest Period or Shelf Life Estimation for Drug Substances or Products (excluding Frozen Products)'' also available as per ICH Q1E (EVALUATION FOR STABILITY DATA) guideline.