Photo Stability Test Chamber Dec 15, 2021
Sunlight is a powerful force. The sun emits radiation in most of the electromagnetic spectrum, including a large amount of ultraviolet radiation. Although part of the solar radiation is absorbed by the earth’s atmosphere, there is still a considerable amount of radiation reaching the earth’s surface (as shown in the picture on the right). Ultraviolet rays can break the molecular bonds in the objects they strike. Most people are familiar with this effect on old paper products and other items. When they are exposed to sunlight, the chemical bonds are broken down, causing the color to fade. This discoloration effect is called photo degradation.

However, the color of the object is not the only thing affected. The chemical properties of objects are affected, so these effects are extremely important to the pharmaceutical, cosmeceutical, and nutraceutical industries. There is a need to avoid chemical breakdown in drugs or vitamins, so it is important to ensure that drugs and nutrients remain stable during the expected shelf life of exposure to light. This is done by testing the light stability of the product. Light stability affects product shelf life, handling and packaging. This test is an important part of the drug development process. Light stability studies are usually conducted in a continuous manner, first testing drugs/supplements. Then, the product is tested first in its direct packaging, by the final marketing packaging that will be placed on the retailer's shelf. These tests can be repeated repeatedly until they prove that the drug can be sufficiently protected from light.

Pharmaceutical manufacturers must establish the stability of their drugs to light. But what makes drug molecules or preparations unstable to light, and how to give them proper protection?
Why do drug molecules degrade under light?
First, drug molecules can directly absorb light. For this reason, the spectrum of the light source must overlap with the absorption spectrum of the molecule to some extent. Therefore, molecules that can absorb light of 320 nm or higher are at risk of photostability.
The second way light causes photodegradation is through a process called photosensitization. This is where another component of the formulation absorbs light energy and then transfers it to the drug molecule, leading to degradation. To illustrate this effect, Figure 4 shows the structure and UV absorption spectrum of Losartan. We do not want losartan to have a photodegradation risk, and it has been proven to be photostable in most formulations. However, in liquid oral preparations containing cherry flavoring, losartan is sensitive to light [2]. Of course, cherry flavoring is colored and can absorb light. In addition, in the presence of oxygen, degradation occurs faster. The photodegradation reaction usually proceeds through the oxidation pathway.

All companies that develop or manufacture drugs require a robust light stability testing process to ensure product quality and regulatory compliance. Inadequate testing can lead to costly delays and lost revenue.

The 1996 guideline CPMP/ICH/279/95 Q1B describes the process of light stability testing of new active substances and pharmaceutical products.
The output of cool white fluorescent lamps is similar to the output specified in ISO 10977 (1993).
The spectral distribution of UVA fluorescent lamps is 320 nm to 400 nm, and the maximum energy emission is between 350 nm and 370 nm. Most waves must be in the range of 320 nm to 360 nm and 360 nm to 400 nm.
The sample should be exposed to at least 1.2 million lux-hours under visible light (VIS) and at least 200 watt-hours per square meter under UVA.

For more information, please refer to thchamber Photo Stability Test Chamber product page.

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