Now in Beta — run your first in silico assessment free, no credit card required.
MolWard
Analyze a Molecule
Home  /  Platform  /  ICH Q3 Impurity Limits
ICH Q3A / Q3B / Q3C / Q3D / Q3E

ICH Q3 Impurity Limits Calculator

Enter the maximum daily dose and route of administration to instantly generate all applicable ICH Q3 thresholds — impurity limits (Q3A/Q3B), residual solvents (Q3C), elemental impurities (Q3D), and the extractables AET (Q3E).

Study Parameters
Q3E AET Parameters
The SCT is the daily dose of a leachable below which no safety concern is expected. Use the default 1.5 ug/day for most drug products — this is the ICH Q3E / USP <1663> consensus threshold for non-specific toxicants. Lower values apply to specific safety concerns:
  • 0.15 ug/day — Cramer Class III or cohort-of-concern structures (e.g. nitrosamines, aflatoxin-like, N-mustards)
  • 1.5 ug/day — Default; general non-specific toxicants (recommended starting point)
  • 120 ug/day — Used for inhalation route with high safety margin (some frameworks)
The SCT drives the AET: all extractables peaks above the calculated AET must be identified and toxicologically assessed.
Ready to calculate.
Results
Enter a dose and click Calculate limits to see all ICH Q3 thresholds here.

How ICH Q3 impurity limits are calculated

The ICH Q3 family sets the maximum amounts of impurities allowed in a drug substance and product. Most limits are driven by a single input — the maximum daily dose (MDD) — because a patient's total daily intake of an impurity is what matters toxicologically, not its percentage alone.

Q3A(R2) / Q3B(R2) — organic impurity thresholds

Reporting, identification and qualification thresholds are read from the maximum-daily-dose bands below (drug substance, Q3A(R2)):

Maximum daily doseReportingIdentificationQualification
≤ 2 g/day0.05%0.10% or 1.0 mg/day (lower)0.15% or 1.0 mg/day (lower)
> 2 g/day0.03%0.05%0.05%

Q3C residual solvents & Q3D elemental impurities

These are fixed health-based limits expressed as a Permitted Daily Exposure (PDE). A PDE in mg/day (or µg/day) is converted to a concentration in the product with:

Concentration (ppm) = 1000 × PDE (mg/day) / daily dose (g/day)

Q3C sorts solvents into Class 1 (avoid — e.g. benzene, carbon tetrachloride), Class 2 (limit by PDE — e.g. methanol, acetonitrile) and Class 3 (low toxicity, ≤ 5000 ppm). Q3D applies the same PDE logic to elemental impurities by route of administration.

Worked example

A product has a maximum daily dose of 800 mg/day (≤ 2 g band):

  1. Reporting threshold = 0.05% = 0.40 mg/day
  2. Identification = 0.10% = 0.80 mg/day (below the 1.0 mg/day cap, so 0.10% applies)
  3. Qualification = 0.15% would be 1.20 mg/day, which exceeds the 1.0 mg/day cap → the limit becomes 1.0 mg/day (0.125%)

Reference: ICH Q3A(R2), Q3B(R2), Q3C(R9), Q3D(R2).

Frequently asked questions

What is the difference between the reporting, identification and qualification thresholds?

Reporting is the level above which an impurity must be reported; identification is the level above which its structure must be determined; qualification is the level above which its biological safety must be justified. They increase in that order.

When does the 1.0 mg/day cap take over from the percentage?

For doses ≤ 2 g/day, the identification and qualification limits are the lower of the percentage or a 1.0 mg/day absolute intake. At higher percentages and moderate doses the mg/day cap becomes the binding limit, as in the example above.

How are residual-solvent limits different from organic-impurity thresholds?

Organic impurities use dose-based percentage thresholds; residual solvents (Q3C) and elemental impurities (Q3D) use fixed toxicological PDEs converted to a concentration for your specific daily dose.