Where different pack sizes are available, the in-use stability test should be applied to the presentation which offers the greatest potential challenge to the product (e.g in the case of an oral liquid product which has borderline preservative efficacy, this should be the largest product; for a product in a semi-permeable container with inert gas head-space and a potential for oxidative degradation, this should be the smallest pack as it is likely to offer the greatest potential for gaseous interchange with atmospheric oxygen)