This is a common and very practical question faced during pharmaceutical development and stability risk assessment.
The question often asked is:
If a product is exposed openly at 40°C / 75% RH for 7 days, how many months of accelerated stability data does this represent?
Here is the scientific and regulatory perspective.
There is no fixed or universal correlation between open exposure studies and ICH accelerated stability studies.
Open exposure and accelerated stability are fundamentally different in their purpose and mechanism.
Open exposure studies are primarily stress or risk-profiling studies.
They are performed to understand moisture sensitivity, oxidation risk, physical instability, hygroscopic behavior, and handling vulnerability of the product.
Accelerated stability studies at 40°C / 75% RH are performed under controlled conditions, typically in the intended market pack, to predict long-term stability behavior.
In open exposure studies, the product is subjected to continuous air contact, unrestricted moisture ingress, and higher oxygen availability.
In accelerated stability, moisture and oxygen entry are governed by packaging barrier properties.
Because of this fundamental difference, degradation kinetics are not comparable on a time-equivalence basis.
For moisture- or oxygen-sensitive products, 7 days of open exposure at 40/75 may sometimes appear more severe than 1 month of accelerated stability.
However, for chemically time-dependent degradation, accelerated stability may show more change than open exposure.
Therefore, statements such as “7 days open exposure equals 1 month or 3 months accelerated stability” are scientifically incorrect unless supported by product-specific data.
The correct way to establish correlation is to generate parallel data.
This involves performing open exposure studies and accelerated stability studies simultaneously and comparing the same stability markers such as assay, impurities, moisture content, dissolution, viscosity, or appearance.
Correlation can only be concluded when the same stability parameter reaches a comparable level under both conditions.
Even then, such correlation is valid only for that specific product, dosage form, and packaging system.
Regulatory agencies consider open exposure studies as supportive or investigative studies, not as a replacement for ICH stability requirements.
The real value of open exposure studies lies in early risk identification, formulation optimization, packaging selection, and handling guidance — not in replacing accelerated stability timelines.
Open exposure studies help us understand how sensitive a product is, while accelerated stability studies tell us how long a product remains stable. Both serve different but complementary purposes in pharmaceutical development.
Read also: Extrapolation and Regression Study in Stability Analysis
Resource Person: Moinuddin Syed. Ph.D, PMP®
