Compositing Samples and the Risk to Product Quality - Pharmaceutical Technology

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Compositing Samples and the Risk to Product Quality
Compositing samples is appropriate under certain circumstances but raises caveats on how and when it should be applied.

Pharmaceutical Technology
Volume 37, Issue 5, pp. 70, 73

Skip-lot and skip-test sampling

Another practice that companies want to do is to do "skip-lot sampling" and literally skip sampling and testing some lots. Given the necessary assumptions, skip-lot testing could be supported statistically but not from a practical point. Again, the risk to product quality is too high.

In Europe, the regulatory agencies require at least an identity test on every drum or container received. That is good practice. That requirement should be expanded to specify that some samples from the middle and bottom of some containers should be taken, and not just samples from the top.

In the past, the industry has tried to argue for "skip-test sampling", meaing that each incoming lot of materials would be tested for identity but some lots would be skipped for a full battery of tests. Again, this type of sampling increases the risk to product quality and, therefore, the patient.

So, how to address this issue? As noted previously, a case needs to be built for compositing that does not include cost savings. This case would include how well do we know the supplier, what historical data can be used, what validation studies are available, and how is risk to the patient minimized? Statistically, good estimates of variability are needed because compositing averages out valuable variation.


Composite sampling may be acceptable when the material is known to be homogeneous or the variability structure is well estimated with high confidence. It is a bad approach, however, when used for critical materials, APIs, or in the absence of information about variability of the material.

Composite sampling is not prohibited by FDA, but it is suspect from the get go. It must be supported by data, facts, and documentation.

Lynn D. Torbeck is a statistician at PharmStat Consulting. tel. 847.424.1314


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