Continued Process Verification: Stage 3 Never Ends

CPV is Stage 3 of process validation. FDA's 2011 guidance restructured validation into three stages, and the change people underestimate is that the third one has no end date.

• Stage 1, process design. Define the commercial process from development knowledge.
• Stage 2, process qualification. Demonstrate the process performs as designed. This is where PPQ batches sit, and it is what most people mean when they say "validation".
• Stage 3, continued process verification. Ongoing assurance that the process remains in a state of control during routine production.

The old model treated validation as an event: three batches, a report, done. The current model treats it as a state you have to keep demonstrating.

EU GMP Annex 15 asks for the same thing under the name ongoing process verification.

What Stage 3 actually requires

A defined monitoring plan. Which parameters and attributes, at what frequency, analysed how. Chosen from the Stage 1 and 2 understanding of what matters, not from what happens to be easy to measure.

Statistical analysis, not just collection. Data accumulating in a system nobody analyses is not verification. The commitment is to detect drift.

A trained person reviewing it, on a defined cadence, with authority to act.

Documented action when the analysis says the process is drifting.

Control limits are not specifications

This is the distinction that decides whether CPV is doing anything.

A specification is the limit beyond which product fails. A control limit, from the process's own variability, is where the process tells you it has changed.

A result inside specification but outside control limits is not an OOS. It is a signal that something moved, and it is the only warning you get before a batch fails. A CPV programme that only reacts at the specification has given up the early warning it exists to provide.

Capability indices such as Cpk quantify the margin. A process running at Cpk 1.0 is meeting specification and has no room, which is a finding worth having before a batch fails rather than after.

What it feeds

CPV output belongs in the annual product review, and the two are often run as one exercise. It should also inform change control: a process trending toward a limit is the reason to change something, and a change is the reason to re-examine the monitoring plan.

Where it fails

A plan that was never revisited. Written at launch, monitoring parameters that turned out not to matter, missing the ones that did.

Trending without limits. Charts with no control limits cannot signal anything, and they are common.

Signals with no action. The chart showed drift for eight months and the review recorded that it was noted. An inspector reading eight months of noted drift has learned something about the quality system.