Stability of dithranol in creams

The stability of the anthrachinone derivative dithranol in creams was studied during storage at temperatures of 4 degrees C and 20 degrees C. Aluminum-coated tubes with 0.1, 0.3 and 0.5% dithranol were stored and samples were analysed immediately and after 3, 6 and 12 months of storage. The 0.3% dithranol cream was also stored in polypropylene tubes. Drug concentration was analysed by high-performance liquid chromatography. All concentrations tested were stable for 12 months of storage at 4 degrees C in aluminum-coated tubes. This means that these low concentrations are sufficiently stable to be prepared in advance for at least 12 months if prepared as described and kept refrigerated. Polypropylene tubes should not be used.