27/28 April 2021
In the FDA Guidance for Industry on process validation, there is also a short section on concurrent validation. Concurrent validation should be used rarely, but may be possible if, for example, products are manufactured infrequently or medically necessary products are needed for short-term market supply.
A tablet manufacturer was criticized in a recent Warning Letter for failing to validate the mixing process. Underdosed tablets, including from validation batches, were discovered during the FDA inspection. In the response letter after the inspection, the company announced its intention to carry out an concurrent validation in order to obtain sufficient data.
The FDA rejected this because the company did not provide sufficient data to show where the variability in the mixing process comes from and how it is controlled. This must be done prior to revalidation. Therefore, the use of concurrent validation is inappropriate because there is not a strong understanding of the sources leading to the variabilities. The FDA then goes on to state that concurrent validation should only be used rarely.
On the FDA website you can find the entire Warning Letter to Allay Pharmaceuticals.