Are peptides light-sensitive? Photostability and ICH Q1B explained
Some peptides are light-sensitive. Tryptophan, tyrosine, histidine, cysteine and methionine residues can be photo-oxidised, especially in solution. ICH Q1B sets the standard photostability test: exposure to at least 1.2 million lux hours of visible light and 200 watt-hours per square metre of near-UV, compared with a dark control.
What does ICH Q1B require?
| Element | Requirement |
|---|---|
| Visible light | Not less than 1.2 million lux hours |
| Near-UV (320–400 nm) | Not less than 200 W·h/m² |
| Light sources | Option 1: D65/ID65-type lamp; Option 2: cool white plus near-UV lamps |
| Controls | Dark control (wrapped in foil) tested alongside |
| Sequence | Forced degradation, then confirmatory testing of substance and product |
Source: ICH Q1B Photostability testing of new drug substances and products
How has the guideline been criticised?
A 2010 critical assessment argued that parts of Q1B are ambiguous, including light-source specification and exposure monitoring, and proposed refinements. An earlier overview set out practical directions for applying the guideline.
Source: A critical assessment of the ICH guideline on photostability testing (Q1B), J Pharm Sci 2010 (PubMed 20135694); ICH guideline for photostability testing: aspects and directions for use, Pharmazie 2003 (PubMed 14703965)
Which peptides are most at risk?
- Tryptophan-containing sequences: photo-oxidation to N-formylkynurenine and kynurenine.
- Tyrosine: dityrosine cross-links and oxidation.
- Peptides with metal complexes or chromophore modifications.
- Solutions far more than lyophilised solids.
How should light-sensitive stocks be handled?
- Store vials in their carton or in amber or foil-wrapped containers.
- Prepare solutions away from direct sunlight and strong bench lighting.
- Use amber or opaque tubes for aliquots.
- Include a dark control when you run your own stability check.
How does Sable document lots?
There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Frequently asked questions
Are peptides sensitive to light?
Some are, particularly those containing tryptophan or tyrosine, and mainly in solution.
What light exposure does ICH Q1B require?
At least 1.2 million lux hours of visible light and 200 W·h/m² of near-UV energy.
What is a dark control in photostability testing?
An identical sample protected from light, used to separate light effects from thermal effects.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- ICH Q1B: ≥1.2 million lux h visible; ≥200 W·h/m² near-UV
- Light-sensitive residues: Trp, Tyr, His, Cys, Met
- References: ICH Q1B; PubMed 20135694, 14703965
- Updated 2026-10-16