as per ICH, most common recommended stability conditions include 25/60, 30/65, 40/75 (Temperature/Relative Humidity)
it also provides some alternative conditions(temperature) for specific products, viz., refrigerated, frozen etc.,
now, the question is, can we similarly justify the alternate conditions for Relative humidity as well. for eg., for a glass-ampoul (/hermetically sealed) injectible product, the relevance of relative humidity can be not totally relevant. Hence, can we take exception or alternate conditions of RH (viz., charge the product only at 25-deg or 40-deg etc.,)
can we extend the similar logic to any container which is proven suitabaly to be impermeable to moisture/water vapor et.c,
Yes, guidelines clearly states that for impermeable packaging materials studies can be conducted on any controlled and ambient relative humidity condition. Below are statements extract from WHO stability studies guidelines TRS 953 Annex 2:
2.2.6.2 FPPs packaged in impermeable containers
Parameters required to classify the packaging materials as permeable or impermeable depend on the characteristics of the packaging material,
such as thickness and permeability coefficient. The suitability of the packaging material used for a particular product is determined by its product characteristics. Containers generally considered to be moisture impermeable include glass ampoules.
Sensitivity to moisture or potential for solvent loss is not a concern for FPPs packaged in impermeable containers that provide a permanent barrier to
passage of moisture or solvent. Thus stability studies for products stored in impermeable containers can be conducted under any controlled or ambient relative humidity condition.
Further to above; impermeable containers defined as impermeable containers
Containers that provide a permanent barrier to the passage of gases or solvents, e.g. sealed aluminium tubes for semisolids, sealed glass ampoules for solutions and aluminium/aluminium blisters for solid dosage forms.
Below is link of useful article that provide comparison of different stability studies guidelines;