Pharmacopoeias vs ICH for impurities: who really takes precedence (and how to avoid mistakes during audits)

If you work in QA/QC/QP/RA, sooner or later you face a question that sounds simple but, during an inspection, becomes a trap:

“Do we need to follow ICH or the Pharmacopoeia?”

The correct GMP answer is not to choose one over the other, but to demonstrate that you know how to integrate both:

ICH = harmonised scientific rationale and the expected reference framework for new products/registrations and robust risk control;
Pharmacopoeias (Ph. Eur., USP, etc.) = legally binding requirements for placing products on the market in specific regions.

This article gives you an audit-ready operational model to decide what to apply, when to apply it, and how to document it, avoiding the most common mistake: formal compliance (“we performed the test”) instead of substantive compliance (“we demonstrated that the risk is truly under control”).

Why “ICH vs Pharmacopoeia” is a false dilemma

In the real world — the one inspectors look at — the logic is this:

If there is an applicable monograph in the target market, you must comply with compendial limits and methods (unless approved justifications/exemptions exist).

Guide to Pharmacopoeias and Impurities …

If ICH identifies risks/impurities not covered by the monograph, you cannot “hide behind” the pharmacopoeia: you must still assess and control them.

Guide to Pharmacopoeias and Impurities …

If there are conflicts, in practice you must:
comply with the legally applicable requirement in the market,
and choose the most defensible and patient-protective strategy — often the more stringent one.

When ICH takes precedence (and what FDA/EMA expect)

In general, ICH takes precedence as a development reference when you are defining or justifying an impurity control system for:

• new products / new registrations,
• significant dossier updates,
• management of critical impurities (for example, mutagenic impurities).

Examples of non-negotiable expectations:

• ICH Q3A/Q3B for organic impurities (reporting / identification / qualification thresholds);
• ICH Q3C for residual solvents (classes, PDE);
• ICH Q3D for elemental impurities (PDE and risk assessment);
• ICH M7 for mutagenic/genotoxic impurities (TTC, risk-based approach).

Important operational note: the guide highlights that, in the EU, some ICH principles are also made legally enforceable through general monographs and general chapters (for example, the integration of ICH Q3A).

When the Pharmacopoeia takes precedence (and why it is dangerous to interpret it in isolation)

When the product is on the market and/or an applicable monograph exists, the logic becomes:

• Ph. Eur. in the EU (implemented through national pharmacopoeias)
• USP in the US
• (and equivalent references for other markets)

Here, the Pharmacopoeia is a legal requirement: if it says “Impurity X ≤ 0.5%” and your ICH rationale would “tolerate” 0.8%, you cannot apply 0.8% in that market.

But the key point is the reverse:
if the monograph is old or does not cover a new impurity (or an emerging risk), you are not automatically covered. The guide states this very clearly: compendial compliance does not exempt you from controlling critical impurities that are not covered.

The multi-region Decision Tree (audit-ready model)

Use this flow every time you need to answer — to yourself or to an inspector — the question: “What are we applying, and why?”

Step 1 — Define the regulatory scenario

• Target markets: EU, US, UK, etc.
• Product: new / lifecycle / generic / biologic
• Dossier: registered specifications and commitments (Module 3)

Step 2 — List the mandatory references

• Applicable monographs (API, DP, excipients where relevant)
• General chapters (for example, residual solvents, elemental impurities, impurities)
• Applicable ICH guidelines based on impurity type

Step 3 — Perform the Gap Analysis (the part that saves you in an audit)

For each category:

• Organic impurities (process-related + degradation)
• Residual solvents
• Elemental impurities
• Mutagenic/genotoxic impurities (including nitrosamines)

Key questions:

• Does the monograph really cover the impurity profile of your process?
• Are there known / undeclared impurities?
• Are the limits justified and aligned with risk?

Step 4 — Choose the defensible strategy

Practical multi-region rule:

• always comply with the compendial requirements of the market,
• apply ICH to close gaps and manage critical risks,
• if there is divergence, apply the most protective solution or document an alternative choice with robust supporting evidence.

Step 5 — Document everything (because “if it isn’t written down, it doesn’t exist”)

Prepare — or verify that you already have — these three documentation elements:

• Impurity mapping (origins, probability, severity)
• Rationale for limits (batch data / stability / toxicology / ICH thresholds)
• Multi-pharmacopoeial strategy (what you do for EU vs US when method/limit changes)

Practical example: a monograph that is “silent” on a modern risk (nitrosamines)

Nitrosamines are the perfect example of why the Pharmacopoeia alone is not enough. The guide highlights that:

• there are no generic numerical limits in Ph. Eur./USP for these impurities,
• a detailed risk assessment and case-by-case controls are expected (ICH M7, toxicological approaches),
• ignoring them today is inspectionally unacceptable.

In practice, this means:
even if the monograph says nothing, the company must be able to show risk assessment + (if needed) testing + limits.

Roles and responsibilities: QC, QA and QP (what inspectors look at)

The guide clearly states a concept that often comes up during inspections:
QC executes, but QA/QP governs and defends.

• QC: correct implementation of methods (compendial or internal), reliable data
• QA: quality system integrating ICH + compendia (change control, periodic review, QRM)
• QP (EU): legal responsibility for batch release → must be able to say “this batch complies with Ph. Eur. and USP” or explain why an alternative strategy is equivalent and authorised.

Mini “audit-ready” checklist (5 questions you will be asked)

1. Which pharmacopoeias apply to the destination markets?
2. Which ICH guidelines have you applied and where are they documented?
3. If the monograph does not cover an impurity from your process, what do you do?
4. How do you manage Ph. Eur. vs USP divergences (methods / limits)?
5. Where are the QA/QP-approved rationales and risk assessments?

FAQ

1) If I follow the USP monograph, am I automatically compliant with FDA expectations?

No. You must also demonstrate method suitability for intended use and show that impurity control is appropriate for your product/process, not just “copied” from the monograph.

2) If Ph. Eur. has a stricter limit than ICH, can I apply the ICH limit instead?

No, not in the EU market: you must comply with the compendial limit.

3) If the monograph is more permissive than ICH, can I stop at the monograph?

No. You must apply ICH to critical impurities that are not covered (substantive compliance).

4) How should a product marketed in both the EU and the US be managed?

You need a multi-pharmacopoeial strategy: standardise where possible, or manage differences through dual testing/bridging and proper documentation.

5) Who should “own” the strategy: QC or QA?

QC implements it, QA governs it, and QP (EU) takes responsibility for release.

6) What is the most frequently cited mistake?

“We followed the pharmacopoeia and nothing else” — without a gap analysis and without a scientific rationale.

Do you want a ready-to-use multi-region strategy with an audit-ready checklist and practical criteria to avoid impurity-related findings? Discover the full guide “Guide to Pharmacopoeias: Impurities and Critical Tests (Multi-Region, ICH vs Compendia)” on guidegxp.com.