Quote from Chief Pharmacist on October 30, 2024, 4:25 pm

It's not mandatory for stability study as it is confirmed by Assay test.

Quote from ariyan on November 1, 2024, 2:45 am

What is the significant change in stability study?

Quote from Chief Pharmacist on November 13, 2024, 9:34 am

In general, “significant change” for a drug product is defined as:

1. A 5% change in assay from its initial value; or failure to meet the acceptance criteria for potency when using biological or immunological procedures;
2. Any degradation product’s exceeding its acceptance criterion;
3. Failure to meet the acceptance criteria for appearance, physical attributes, and functionality test (e.g., color, phase separation, resuspendibility, caking, hardness, dose delivery per actuation); however, some changes in physical attributes (e.g., softening of suppositories, melting of creams) may be expected under accelerated conditions; and, as appropriate for the dosage form:
4. Failure to meet the acceptance criterion for pH; or
5. Failure to meet the acceptance criteria for dissolution for 12 dosage units.

Quote from ard on January 31, 2026, 3:56 pm

Why a photostable drug substance degrading during photostability testing?

Quote from Chief Pharmacist on January 31, 2026, 4:05 pm

We typically expect photodegradation only for molecules that absorb light directly at or above 320 nm. However, this is just one of the two photodegradation mechanisms.

A molecule that doesn’t absorb light itself can still degrade through photosensitization.

This happens when other formulation components absorb light. Then that energy is transferred within the system to degrade the drug substance, often via oxidation pathways. This explains why some API are photostable in one formulation but not in another.

Let this be a reminder that photostability is not just about light sensitivity.

It’s about understanding the mechanism underpinning the degradation due to light exposure.

And that's what turns data into understanding.