Draw or import a structure, then simulate hydrolytic, oxidative, photolytic, and thermal stress to map theoretical degradation pathways.
Forced degradation deliberately stresses a molecule beyond normal storage to reveal its intrinsic instabilities. Under ICH Q1A and Q1B it serves three purposes: mapping likely degradation pathways, developing stability-indicating methods, and supporting mass-balance for the impurity profile.
| Stress | Typical condition | Chemistry probed |
|---|---|---|
| Hydrolytic | Acid / base, aqueous, heat | Esters, amides, lactams, carbamates cleave |
| Oxidative | Hydrogen peroxide, radical initiators | Thioethers, amines, activated positions oxidise |
| Photolytic | ICH Q1B light exposure | Chromophores, alkenes, N-oxides rearrange |
| Thermal / humidity | Elevated temperature ± humidity | Rearrangement, decarboxylation, solid-state change |
Susceptibility is governed by which functional groups are present, so the likely degradants can be reasoned from structure before a single vial is stressed.
Aspirin (acetylsalicylic acid) under hydrolytic stress has a classic, well-documented pathway: the acetyl ester hydrolyses to give acetic acid and salicylic acid — the reason aged aspirin smells of vinegar.
Reference: ICH Q1A(R2) and Q1B; Baertschi et al., Pharmaceutical Stress Testing, 2nd ed.
Commonly around 5–20% loss of the parent — enough to generate the primary degradants and challenge the analytical method, but not so much that secondary/tertiary products dominate and obscure the real pathway.
No. It is a worst-case probe to find possible degradants and prove the method can see them; actual shelf life comes from real-time and accelerated stability studies (ICH Q1A/Q1E).
If the loss of parent is not accounted for by the sum of detected degradants, a degradant may be missed (e.g. UV-invisible or volatile) — a signal the method is not yet fully stability-indicating.