The Stratified Sampling Approach in Process Validation : Pharmaguideline

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The Stratified Sampling Approach in Process Validation

Drug manufacturing is a perfectly systematic process that relies primarily on quality control to produce quality products.
Pharmaceutical manufacturing is a perfectly systematic process that primarily relies on quality control to produce quality products. The goal of quality control is to reduce batch failures and defects during manufacturing by taking steps at every manufacturing stage. Therefore, the sampling of the intermediate and final products is very important. One more considerable approach to validate the manufacturing process is to use stratified sampling.

Importance of Process Validation

process validation

Process validation is useful to ensure that the quality of the finished product meets the product specification and regulatory requirements. The method used for validation depends on the type of production method. But there are three most common methods used experiment, sampling, and statistical analysis. Each method has its specific advantages and disadvantages, so it is important to choose the correct method for specific validation requirements. When the process has low variability, the experimentation method can be used but when the process has high variability then it is required to use sampling or statistical analysis.

Stratified Sampling

The stratified sampling method is used to take samples from a population in which samples are not directly proportional to the size of population. This sampling technique is often used in process validation in pharmaceuticals where it is important to collect data from different parts of the manufacturing process.

The stratified sampling approach can be divided into three steps 1) selecting a sample 2) selecting a stratum and 3) selecting the samples with the stratum. In pharmaceutical practice, these three steps are combined together. In the first step, a random sample is taken from the population. In the second step, it is decided from which steps of the manufacturing process samples will be taken. In the third step, samples are taken from the strata chosen from the second step.

How to Conduct a Stratified Sample Run

In process validation, it is important to use stratified sampling to reflect the overall population in the sample. The stratified sampling ensures that the collected sample is representative of the whole batch that is drawn. The following are three steps to conduct the stratified sampling.

1. Choose an Appropriate Sampling Unit: Select a batch for sampling so that the process validation is being done.

2. Determine the Strata: Make the strata of the batch in which samples need to be taken

3. Choose a Representative Sample from each Strata: Take samples in different strata to ensure that the sample is representative of the whole batch.

Application of the Stratified Sampling Approach

In pharmaceutical process validation, stratified sampling is used very useful. This type of sampling helps to study the manufacturing process more closely by randomly selecting a part of the population. It is beneficial in process studies because it helps to ensure that the study is reflective of the actual process. To implement it in pharmaceutical process validation, first determine the process validation batch. Next, create a list of groups or strata within the batch sampling. Each stratum should be geographically different from each other.
Related: Different Stages of Tablet Manufacturing Process  

For example, if you are validating the compression stage of tablet manufacturing and the total batch size is 1,50,000 tablets and it takes 60 minutes to compress all tablets. Then take samples during the compression process at 20 min, 40 min and 60 min. you can add more variables i.e. compression machine speed, low, medium and high speed. You can add different variables (factors that can affect the product quality) at different stages of manufacturing like blending, drying, granulation, compression and packaging.

In this way, stratified sampling helps to validate the manufacturing process at different variables that can affect the product quality. It helps to ensure that the manufactured product doesn’t get affected by the factors that can affect the quality of the product.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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