As a guide to good pharmaceutical practice it is suggested that mixtures recommended to be 'freshly prepared' should be prepared not more than 24 hours before issue to the patient. Mixtures recommended to be 'recently prepared' should be stored in unopened bottles in the dispensary for not more than 3 months. Should there be any doubt, the pharmacist should be consulted. An increase in temperature usually increases the rate of chemical reaction. Refrigeration may prolong shelf-life of a medicament that is unstable in room temperature but solid particles may grow and precipitate in a suspension.
Many drugs show slow oxidation in the presence of atmospheric oxygen.
If the rate of degradation is significant, the addition of an anti oxidant may be needed. This can be reduced by the use of light-resistant containers, or more effectively, by storage in the dark. High humidity brings about the deterioration of effervescent tablets and solid preparations that contain hygroscopic materials. The adverse effects of humidity can be avoided by the use of moisture-proof containers. The basic requirement for a container is that it should not interact with the formulation.