How many PPQ batches are enough?

Why

Three batches became an industry habit long before the current guidance. The FDA's 2011 guidance moved away from fixed numbers. It describes PPQ in terms of sufficient statistical confidence within and between batches, based on the overall level of process understanding, and recommends objective statistical measures where feasible.

EU Annex 15 is more specific but makes the same point. The number of batches and samples should follow quality risk management, allow the normal range of variation and trends to be established, and be justified by each manufacturer. It adds that a minimum of three consecutive batches under routine conditions is generally considered acceptable, that a different number can be justified considering standard methods and similar products at the site, and that three batches may need supplementing with data from later batches through ongoing verification.

The practical answer is to argue from what you know. A well-understood platform process at a site already making similar products might justify three. A new process with variable raw materials might need more, or three PPQ batches followed by heightened Stage 3 sampling until variability estimates are reliable.

Three batches give very little statistical power to estimate between-batch variability, so the number is a decision about risk, not a compliance checkbox.