# Stability extrapolation

Is there any guideline restricting to extrapolate re-test period of API from 36 month on-wards?

I mean, as per ICH we can extend re-test period for the product storing at CRT by using below formula…
Y = 2X or Y = X+12 which is lesser in both.

I have 36 month long term [25°C/60%RH] & 6 months accelerated data [40°C/75%RH] and stability studies are on-going.
Based on this data can I assign 48 months re-test?

Is there any guideline restricting to assign 48 months re-test if i have 36 months data.

You are using the wrong equation! The potency decreases with time (not increases), thus the Arrhenius equation. In addition, you can only submit 36 month data and you have to understand your drug product including the impurity profile. See attached;

You can also use semi-log paper to plot the drug product potency over time.

Hi Boomer,
As per provided US FDA guide line, the same equation is claiming.
Please see the page # 5 first para graph

“The proposed retest period or shelf life can be up to twice as long as, but should not be more than 12 months beyond, the period covered by long-term data”

As a API manufacture i can assign 48 months re-test based on 36 months long term data, if no significant change observed. ICHQ1E also supporting the same.

Please revert by keeping in view of API manufacture…

Perhaps. But the question is are we talking about the API or it’s related substances? The Arrhenius plot applies only to the API. Its related substances (RS) grow over time and your equation (Y = 2X) tells me it is exponential and could be OOS very rapidly. Have you set specifications for your RS(s). Usually, the equation at any time point is;

Decrease in API potency in umoles = Sum of growth in RS(s) in umoles

In short the drug product can rapidly become OOS because of the RS(s) but it doesn’t hurt to apply if you know your drug product.

It also depends on your drug product and where you are registered to sell it. If it is a ‘generic’ (ANDA) then your specifications are constrained to the whatever the originator had. If it is an NDA you are the 1st down this road and may want to plant a few land mines.