ICH Q1B - Photostability Testing of New Drug Substances and Products

What it says

ICH Q1B describes a stepwise approach to photostability testing of new drug substances and products. Studies begin with forced degradation work to understand light sensitivity, followed by confirmatory testing on a batch with a defined minimum exposure: not less than 1.2 million lux hours of visible light and not less than 200 watt hours per square metre of near ultraviolet energy. Testing starts with the drug substance, then the product outside its pack, then in the immediate pack and, if needed, in the marketing pack, always with dark controls for comparison.

Paraphrased for plain-language clarity. Always verify against the current published regulation text.

What it means in practice

• Photostability results drive packaging choices and storage statements such as protect from light, so the study conclusions feed directly into the product label and the container closure system.
• The light dose has to be measured, not assumed. Light sources, lux meters, radiometers or actinometry need to be controlled and calibrated so that the minimum exposure is demonstrated.
• A dark control, protected from light but kept under the same temperature conditions, separates the effect of light from the effect of heat, which is why it is a standard part of the design.

What inspectors look for

• Whether photostability studies followed the guideline or documented a scientific justification for any departure from it.
• Whether light exposure was measured and the equipment calibrated, and whether dark controls were included.
• Whether the packaging and storage statements are supported by the photostability data.

Related regulations