Effect of some formulation adjuncts on the stability of benzoyl peroxide.

The stability of benzoyl peroxide in polyethylene glycol ointment base and some liquid vehicles (acetone, ethanol, propylene glycol, and their mixtures) was studied. Some solutions also contained an additional ingredient (acetanilide, benzoic acid, chlorhydroxyquinoline, and hydroxyquinoline) as a possible stabilizer. Benzoyl peroxide decomposed very fast (first-order K value 0.028 day-1 at 24 degrees) in polyethylene glycol ointment base. At 50 degrees, the potency of benzoyl peroxide in polyethylene glycol ointment base decreased to less than 1% in 5 days. Decomposition in solutions is complex. Considering acetone as a standard vehicle, ethanol improved the stability of benzoyl peroxide and propylene glycol had an adverse effect on the stability. Of the stabilizers studied, only chlorhydroxyquinoline improved the stability.