ICH Q3 — Impurities

The Q3 family: organic impurities in the drug substance (Q3A) and product (Q3B), residual solvents (Q3C), and elemental impurities (Q3D) — reporting, identification, and qualification thresholds.

Outline and talking points — the full write-up is still to come.

What this page covers

  • Q3A(R2) — impurities in new drug substances: reporting / identification / qualification thresholds tied to maximum daily dose.
  • Q3B(R2) — degradation products in new drug products (the ones Q1 stability testing tracks).
  • Q3C(R9) — residual solvents: Class 1 (avoid), Class 2 (limit, PDE-based), Class 3 (low toxic potential).
  • Q3D(R2) — elemental impurities: the permitted daily exposure model and the risk assessment that replaced USP <231> heavy metals.
  • Related: M7 — mutagenic impurities (the “cousin” of Q3 the class should know exists).

Lecture prep — open items

  • The thresholds table, with a dosing example students compute themselves.
  • How a Q3 threshold becomes a specification limit becomes a required method sensitivity (LOQ).
  • Q3D risk assessment walkthrough for a real dosage form.