Enter Maximum Daily Dose of API in milligram (mg)  
References:

ICH Guideline: Q3A - Impurities in New Drug Substances

Maximum Daily Dose1 Reporting Threshold2,3 Identification Threshold3 Qualification Threshold3
≤ 2 gm/day 0.05% 0.10% or 1.0 mg per day intake (whichever is lower) 0.15% or 1.0 mg per day intake (whichever is lower)
> 2g/day 0.03% 0.05% 0.05%
1. The amount of drug substance administered per day
2. Higher reporting thresholds should be scientifically justified
3. Lower thresholds can be appropriate if the impurity is unusually toxic

ICH Guideline: Q3B - Impurities in New Drug Products

Threshold type Maximum Daily Dose1 Threshold2,3
Reporting Threshold ≤ 1 g 0.1%
> 1 g 0.05%
Identification Threshold < 1 mg 1.0% or 5 µg TDI, whichever is lower
1 mg - 10 mg 0.5% or 20 µg TDI, whichever is lower
>10 mg - 2 g 0.2% or 2 mg TDI, whichever is lower
> 2 g 0.10%
Qualification Threshold < 10 mg 1.0% or 50 µg TDI, whichever is lower
10 mg - 100 mg 0.5% or 200 µg TDI, whichever is lower
>100 mg - 2 g 0.2% or 3 mg TDI, whichever is lower
> 2 g 0.15%
1. The amount of drug substance administered per day
2. Thresholds for degradation products are expressed either as a percentage of the drug substance or as total daily intake (TDI) of the degradation product. Lower thresholds can be appropriate if the degradation product is unusually toxic.
3. Higher thresholds should be scientifically justified.

FDA form for Justification of Specification for drug substance and drug product

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