What should happen when a qualified supplier later shows adverse quality trends?

Why

ICH Q10 says the company remains responsible for the quality of purchased materials and should monitor supplier performance and implement improvements, not just qualify once. EU GMP Chapter 5 asks for supplier selection, qualification, approval and maintenance, with the supporting evidence documented and the risk of the supply chain considered. US regulation lets a manufacturer accept a supplier's report of analysis instead of full testing only if it runs at least one identity test and validates the supplier's results at appropriate intervals.

A trend undermines that reliance. Suppose an excipient supplier's particle size results creep toward the upper limit over six lots, and your own blend uniformity worsens. The first step is to confirm the trend in your own data, then notify the supplier formally and ask for their investigation.

Meanwhile, go back to full testing of incoming lots rather than relying on the certificate, and assess lots already used. If the supplier cannot explain or correct it, a for-cause audit is justified. Suspension depends on risk and alternatives.

Losing a sole source can harm patients through shortage, which ICH Q9(R1) counts as a quality risk too, so the decision balances product risk against supply risk and is documented. Changing to a new supplier is itself a change needing qualification and possibly regulatory notification.