Due to their stiff nature, pastes can be applied accurately to a particular lesion such as chronic eczema and psoriasis, and are therefore useful for the local application of irritating drugs. Spirits Are alcoholic or hydroalcoholic solutions of volatile substances prepared usually by simple solutions or by admixture of the ingredients. Spirits require storage in tight, light-resistant containers to prevent loss by evaporation and to limit oxidative changes. Suspensions Are preparations of finely divided, undissolved drugs dispersed in liquid vehicles. The particulate matter of a suspension may settle slowly from the liquid vehicle in which it is dispersed and therefore suspensions should be shaken well before use to ensure uniform distribution of solid in the vehicle and thereby uniform and proper dosage.
Suspensions require storage in tight containers.
Tinctures Are alcoholic or hydroalcoholic solutions prepared from vegetable materials or from chemical substances. Tinctures require storage in tight, light-resistant containers, away from direct sunlight and excessive heat. Podophyllin tincture and iodine tincture are examples. This may explain the difference in shelf life for the same ointment in areas of different latitude if stored in ambient temperature.