The stability of betamethasone-17-valerate in semi-solid bases

The stability of betamethasone-17-valerate in semi-solid bases has been investigated. Emphasis has been placed on the stability problems which could arise upon dilution of proprietary preparations by the use of model systems. Betamethasone-17-valerate has been shown to decompose to betamethasone-21-valerate and betamethasone alcohol. Quantitation of the decomposition was by direct densitometry on thin layer chromatographic plates. The decomposition was found to be an apparent first order process and to depend on the diluent used and its concentration. Attempts were also made to relate the rate of decomposition to the pH of the base used, and to stabilize the products.