What Is Photostability Testing Of New Drug Substances: Learn in 5 minutes

Photostability Testing plays a crucial role in ensuring the quality, safety, and efficacy of new drug substances and their pharmaceutical products. Many pharmaceuticals are highly sensitive to UV and visible light, and exposure can lead to degradation or the formation of harmful impurities. Photostability studies help identify these light-induced changes, enabling better control over product formulation, packaging, and shelf life.

In this article, you will learn:

1. What photostability is
2. The standard procedures for conducting photostability testing
3. The key advantages of photostability studies
4. Real-world case studies
5. Frequently asked questions (FAQs) related to photostability

Photostability Testing

In photostability studies, the intrinsic photostability characteristics of active pharmaceutical ingredients (APIs) or dosage forms are established by UV light exposure.
Photostability testing is performed on a single registration batch of drug substance and drug product.

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The Standard Procedures for Conducting Photostability Testing

Three samples (Let us say A, B and C) are withdrawn from the same lot of the representative API (sample packed in the official packing).

• Sample A is tested immediately as per the method of the API monograph (this represents the Control sample)
• Sample B is transferred to a transparent glass dish and spread such that a 2 to 3 mm layer is formed (this represents the unprotected stressed sample).
• Sample C is transferred to a transparent glass dish and spread such that a 2 to 3 mm layer is formed. It is covered with Aluminum foil. (this represents the protected stressed sample).
• The above two stressed Sample B (unprotected stressed sample) and Sample C (protected stressed sample) are exposed to irradiation of controlled intensity 750W/m² for 7.1 hours. The received dose of the irradiation for this period is about 463 hours in the near UV range (more than twice the required minimum dose and 1200 klux hours in the visible range),
• At the end of the exposure, both Sample B (unprotected stressed sample) and Sample C (protected stressed sample) are analysed by the stability indicating method.

Result evaluation

• If the colour of sample B (unprotected stressed sample) and sample C (protected stressed sample) should be compared. If the color of sample B matches the color of sample C that indicates the API is not UV-light sensitive.
• If the color of sample B (unprotected stressed sample) and sample C (protected stressed sample) should be compared. If the color of sample B does not match the color of sample C it indicates that the API is UV-light sensitive.
• Sample B (unprotected stressed sample) and sample C (protected stressed sample) should also be analysed for assay and related substances test and results should be compared.

Photostability Acceptance criteria

The sample is examined for description, clarity, the colour of the solution, related substances, chiral purity test (if applicable) and assay test as per monograph. The sample must comply with all these tests.

How to Identify Photostability Impurities?

The following approaches should be applied to identify the Photostability Impurities:

• Review of ROS(Route of synthesis) with reagents and chemicals: ROS of SM, KSM, and purchasing material gives insight into potential impurities. These potential impurities can be synthesized and used to actual degradation impurities identification.
• Literature/Reported impurities (from the published literature): The literature reported impurity is very helpful in identifying actual degradation impurities based on retention time
• Spike study: In the spiked study, a sample containing the probable impurities is spiked with the actual probable impurity standard to confirm the probable impurities.
• Isolation and characterisation: This is a complex and costly activity and it takes along time.

Why is the stability chamber used for UV light exposure?

Visible light falls between the ultraviolet and infrared regions of the electromagnetic spectrum. Ultraviolet light has a shorter wavelength and is more energetic. Ultraviolet light can cause greater harm to our pharmaceuticals or products.
In addition to visible light, sunlight also contains ultraviolet light. This ultraviolet light is usually filtered by the time sunlight reaches our pharmaceuticals or pharmaceutical products. This filtering effect is provided by the Earth’s atmosphere. Even ordinary glass, such as window glass, can remove some UV light. That is why a stability chamber is used for UV light exposure on the sample.

Case Study: Pharmaceuticals that are Sensitive to Ultraviolet Light

The APIs like Rosuvastatin and atorvastatin are highly sensitive to UV light. That is why special precautions are taken while handling these APIs.

Advantages

• To see the impact of UV light on the stability of pharmaceuticals
• Help in the development of stability indicating method
• Help in defining storage condition
• Help in defining packaging condition

Conclusion

hotostability testing is a critical component in the development and quality control of pharmaceutical products. By identifying how drug substances respond to light exposure, these studies help prevent degradation, ensure consistent efficacy, and support regulatory compliance. Understanding and applying photostability principles not only protects patient safety but also enhances the stability and marketability of drug products. As regulatory expectations evolve, integrating robust photostability testing into the development process remains essential for successful product lifecycle management.

I hope this article has helped you understand the Photostability study and its importance in pharmaceutical development. Now you can independently perform Photostability study and testing during routine analysis.

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FAQS on Photostability Study

How do you test for photostability?

Three samples are taken from one representative API lot. One sample is analysed immediately and the result is reported. The second sample is exposed to irradiation of controlled intensity 750W/m² for 7.1 hours in unprotected conditions. The third sample is exposed to irradiation of controlled intensity 750W/m² for 7.1 hours in protected conditions. Then the second samples and third samples are analysed by stability indicating validated method for description, solubility, impurity profile and assay tests and results are compared.

Which instrument is used to perform photostability?

A Photostability chamber is used to perform photostability

What is the purpose of photostability study?

The purpose of the photostability studies evaluate the intrinsic photostability characteristics of active pharmaceutical ingredients (APIs) or dosage forms.

How many samples are taken for the Photostability study?

One production sample is taken for the Photostability study

References

• https://database.ich.org/sites/default/files/Q2%28R1%29%20Guideline.pdf

Abbreviations

• AMV: Analytical method validation