Stability testing is a process that provides evidence on how the quality of a pharmaceutical product varies over a given period. This process shows how a drug will vary in quality under the influence of environmental changes, including temperature, light, or moisture.
Stability testing is designed to include testing of attributes that are susceptible to change during storage, which is likely to influence the quality, efficiency, and safety of the drug. Testing majorly covers physical, chemical, and microbiological characteristics such as:
- Physical: Appearance, melting point, clarity, and colour of the solution, water content, pH levels, dissolution characteristics, viscosity, and crystal modification of the drug.
- Chemical: Assay, degradation, related substances, and the residual solvents found.
- Microbial: Growth in microorganisms and efficiency of the preservative contents like antioxidants are checked.
Frequency of Testing:
The frequency of testing for long-term studies should ideally be sufficient to establish the stability profile of a drug for a speculated period. For substances with proposed retest periods of 12 months, the frequency of testing at storage conditions is usually conducted every three months in the first year and every six months for the second year. After that, annual tests are conducted.
It is recommended that test frequency for intermediate storage conditions is a minimum of four time points, and can exceed for a 12-month study. For conditions like accelerated storage, a frequency of a minimum of three points for a six month study period is recommended.
For every different formulation type, manufacturers determine the quality of the drug that needs to be examined. From there, testing at varied temperature and humidity conditions are carried out. Test parameters are evaluated and tested according to a company’s internal procedures. The evaluations need to allow the deduction of the stability of the product, both predicted and real stability.
Manufacturers must take certain considerations into account, especially with products that do not have any official guidelines for stability testing. These include:
- The conditions that could potentially accelerate or predict the effects of stress on product consistency.
- Changes to a product’s aesthetic properties, including colour, fragrance, or texture.
- Variations in the manufacturing process could cause changes in the product.
- Packaging and the effect it could have on the formula.
Steps For Stability Testing
A basic format most companies use for this process includes seven basic steps:
- Batch Production: Calculation of how much of a substance needs to be produced based on the number of samples that are used for testing.
- Product Container Filling: The product needs to be filled in proper packaging, and it is best to test both the container used during testing and the final packaging of the product.
- Initial Test (TimePoint Zero): When samples are filled into suitable containers, all the physical, chemical, and microbiological characteristics are put into the initial testing phase.
- Product Storage: The testing process requires different physical conditions to note changes. Optimum temperature and humidity conditions to store a product are noted.
- Evaluation: During long-term studies for a pharmaceutical product, the frequency of testing is set to be sufficient to establish a clear product stability profile. Evaluations need to be carried out at frequent intervals depending on the kind of process invoked.
- Stability determination: After the study period has defined basic characteristics and variation of the product to different environments, there needs to be a clear idea of whether the formula is stable or not. Until this is established with certainty, testing needs to be carried out. If the results are indefinitely unsatisfactory, the product won’t make it to the market.
- Conclusion report: When the testing is completed, a thorough conclusion report needs to be compiled. This report must include all the testing methods and findings of the results. The report generally includes:
- Identification of the lab conducting the testing (if any third-party contractor is hired);
- Identifying the product;
- The samples of all primary packaging material used in the testing process;
- Description of the different methodology used to determine the product’s minimum durability, the study conditions employed, and results of the study;
- The signature of the person who was responsible for the undertaking of the study is a must.
It is beneficial for pharmaceutical manufacturers to have routine stability testing protocols in the lifecycle of the products. The products must respond positively, and the results are up to the standard of the official regulatory body guidelines to pass into the market.
Stability testing also allows the consumers to be aware of the conditions on when they should store their products in and when they should chuck them out. This avoids any medical issues that could potentially cause a threat to the consumer’s health.