Statistical Sampling: an Underestimated Element of Process Validation?
Recommendation
11-13 November 2025
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In a recent FDA Warning Letter, the FDA criticized inadequate process validation for a semi-solid dosage form. What exactly did the FDA find inadequate?
The validation studies were criticized for not reflecting inter- and intra-batch variability. In particular, there was criticism that the sampling was random. The viscosity sampling scheme does not lead to statistical confidence in process performance.
In a second Process Performance Qualification (PPQ) study, the influence of a critical excipient on viscosity was to be shown. Again, the FDA criticized that no inter-batch variability was demonstrated. This is not surprising, since only one run was performed.
As measures, the FDA requires:
- a validation programme, starting with product development, the validation itself and the control/monitoring of the processes with regard to intra- and inter-batch variability
- an equipment and premises qualification programme
- a programme for Process Performance Qualification and Continued Process Verification measures.
You can find the entire Warning Letter on the FDA website.
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