Terry Redman posted an article on PharmaQbD.com recently entitled 'If QbD is the Map, Then PAT Is the GPS' and I posted a reply that I am reproducing here; you can add your own thoughts on the PharmaQbD site if you like.
Analogies are useful when trying to understand new concepts and Terry’s is witty and readable. It’s a shame that these analogies appear to be needed when we are several years down the line with QbD. I tend to think of both maps and GPS in a positive light, although both can be misleading from time to time.
If I had to use travel metaphors to explain QbD and PAT I would say:
- QbD is a way of driving safely and defensively, so that quality targets are met;
- The human / engineer / scientist / organization provides the map, steering, fuel and the motive power;
- Software and hardware tools may allow a change of gears;
- PAT instrumentation is the rear view mirror, telling us what has happened, after it has happened;
- Predictive modeling tools are the windscreen and the headlights, leveraging other information to predict the future, i.e. before it happens. That is what enables design.
You could summarize by saying that measurements, however numerous, sophisticated and timely, are not a substitute for thinking.