•Guidance for in-use preservative t

•Guidance for in-use preservative testing is described in an EC guideline (EMEA/CV/MP/127/95 1 which specificaIIy states that additionaI testing may be applicable to multi-dose or topical dosage forms if a specific problem (in terms of stability of the product) has been identified after the product has been opened. For example, this situation would apply to a product with an active ingredient that is subject to oxidative degradation and has been packed in a completely filled oxygen-impermeable container (e.g. a pharmacy bulk pack). Its gIass package provides a barrier to oxygen so that oxidative stress would not be seen during the normal stability program. The situation would be exacerbated if the active ingredient, the antimicrobial preservative or any other critical formulation component exists in a reduced form. A real concern would exist about the potentiaI for oxidative degradation of the formulated product upon repeated exposure to oxygen during use.