Drug Stability Testing – Simple Explanation:
Drug stability testing is done to find out how long a drug remains safe and effective under different environmental conditions. It helps determine the shelf life, storage conditions, and expiry date of medicines.
Here’s how it is tested step by step:
1. Purpose of Stability Testing
The main goal is to see how factors like temperature, humidity, light, and time affect a drug’s:
- Physical appearance (color, texture)
- Chemical composition (potency and degradation)
- Biological activity (effectiveness)
- Safety (no harmful by-products)
2. Types of Stability Tests
a) Long-Term Testing:
Drugs are stored at normal room conditions (about 25°C and 60% humidity) for 12 to 24 months.
- This shows how stable the drug is during real storage conditions.
b) Accelerated Testing:
Drugs are kept at higher temperatures (around 40°C and 75% humidity) for a few months.
- This helps predict the shelf life faster.
c) Stress Testing:
Samples are exposed to extreme heat, light, pH changes, or moisture to see how the drug breaks down.
- It helps identify possible degradation products.
d) Intermediate Testing:
Used when results from accelerated tests show instability.
- Conducted at moderate conditions (like 30°C and 65% humidity).
3. Parameters Measured
During testing, scientists check:
- Appearance: any change in color, odor, or texture.
- Assay: how much active ingredient remains.
- pH: for liquid formulations.
- Dissolution rate: how well the drug dissolves.
- Degradation products: using techniques like HPLC or mass spectrometry.
- Microbial limits: to ensure no contamination.
4. Analytical Methods Used
To measure stability, chemists use tools such as:
- High-Performance Liquid Chromatography (HPLC) – to detect impurities and degradation.
- Mass Spectrometry (MS) – to identify breakdown products.
- UV/Visible Spectroscopy – to check concentration.
- Thermal Analysis – to study heat sensitivity.
5. Determining Shelf Life
Data from all tests are analyzed to decide how long the drug can stay effective.
- The period during which the drug remains within its specifications is its shelf life.
- The storage conditions (e.g., “Store below 25°C” or “Protect from light”) are also set based on these results.
6. Importance of Stability Testing
- Ensures drug safety and quality over time.
- Helps set the expiry date.
- Prevents use of degraded or harmful medicines.
- Fulfills regulatory requirements from agencies like the FDA or WHO.
In short:
Drug stability testing checks how long a medicine stays safe, effective, and unchanged under different conditions. It involves long-term, accelerated, and stress tests, and uses scientific methods like HPLC and MS to monitor changes and decide the drug’s shelf life and storage conditions.