Top 10 interview questions about Stability studies.
1. What are stability studies and why are they important?
Stability studies determine how the quality of a drug substance or product varies over time under the influence of environmental factors (e.g., temperature, humidity, light). They are essential for setting shelf life, storage conditions, and retest periods.
2. What are the different types of stability studies?
There are several types:
- Long-term stability (e.g., 25°C/60% RH)
- Accelerated stability (e.g., 40°C/75% RH)
- Intermediate stability
Stress testing (e.g., heat, humidity, oxidation, light, acid/base) These help understand degradation mechanisms and shelf life.
3. What guidelines are followed for conducting stability studies?
International Conference on Harmonization (ICH) guidelines, particularly ICH Q1A to Q1F, are the primary references. They define study design, storage conditions, time points, and data evaluation criteria.
4. What is a stability-indicating method?
A stability-indicating method is an analytical procedure that accurately and precisely measures active ingredients without interference from degradation products, impurities, or excipients. It ensures the method can detect changes due to degradation.
5. What are typical conditions for long-term and accelerated stability studies?
- Long-term: 25°C ± 2°C / 60% RH ± 5% for 12-60 months
- Accelerated: 40°C ± 2°C / 75% RH ± 5% for 6 months
These simulate real-world and stress conditions to estimate product stability.
6. What is the purpose of intermediate stability testing?
Intermediate testing (e.g., 30°C/65% RH) is used when a product fails accelerated conditions but performs well under long-term storage. It helps to understand how moderate stress impacts product stability.
7. What are significant changes in stability testing?
A significant change refers to any change that affects the quality or safety of a product, such as:
- Assay below 90% of label claim
- Appearance changes
- Failure in dissolution or pH specs
- Formation of unacceptable levels of degradation products
8. How are stability study samples stored and monitored?
Samples are stored in stability chambers with controlled temperature and humidity. These are continuously monitored with alarms and data loggers. Periodic sampling is done at predefined intervals (e.g., 0, 3, 6, 9, 12 months).
9. How is shelf life determined from stability data?
Shelf life is estimated by analyzing degradation trends (often using regression analysis) to determine the time when the product falls below specification limits. It must be supported by statistical and analytical data.
10. What is the difference between real-time and accelerated stability?
- Real-time stability uses actual market storage conditions over time to confirm shelf life.
- Accelerated stability uses higher-than-normal stress conditions to predict long-term stability in a shorter time.
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