Question
Posted on: April 8 2014Stability of Betametasonedipropionate,-valerate in Cremes.
As an ester, betametasonedipropionate is practically insoluble (0, 7mg/L) in water, but soluble in lipophilic solvents. In most corticoid (both in specialities and in Magistralen) the water phase is buffered (pH 4-5) for the sake of stability, while we assume that the cortico esters (betametsaondipropionate, Betametasone valerate) migrate to The fat phase. We suspect that these cortico-esters take place in the interphase in a two-stage system. This could explain the rearrangement of Betametasone-17-valerate to the less-active 21-valerate at ph > 6 (water phase), as well as the ester hydrolysis in creams at ph > 7. This would then apply to both O/W and w/o emulsion types. Is This reasoning correct?
Answer
I would not worry too much about this. After all, the TMF publishes a hydro-alcoholic solution with both constituents. The shelf life is set at two months. Whether the corticosteroids will migrate to the fat phase depends on its composition. I am not convinced that these corticosteroids are to a significant extent soluble in any fat or greasy ingredient. The water phase buffing is definitely recommendable.