Pharmaceutical Impurities Calculation

Impurity is a component of any drug product that is not the drug substance or an excipient in the drug product. It is a major concern for pharmaceutical finished products and should be controlled through the product life cycle.

Calculation of Impurities in Drug Products as per ICH

1. When Maximum Daily Dose of a Drug is 500 mg

• Reporting threshold: 0.1%
• Identification threshold: 0.2%
• Qualification threshold: 0.2%

2. When Maximum Daily Dose of a Drug is 10 mg (10000 mcg)

• Reporting threshold: 0.1%
• Identification threshold: 20 mcg/10000 mcg × 100 = 0.2%
• Qualification threshold: 0.5%

Note: Please see the below attachment-1 of Impurities Thresholds (ICH Q3B)

Impurities Thresholds

• Identification Threshold: A limit above (>) which a degradation product should be identified.
• Qualification Threshold: A limit above (>) which a degradation product should be qualified.
• Reporting Threshold: A limit above (>) which a degradation product should be reported.

Calculation of Impurities in Drug Substance as per ICH

1. When Maximum Daily Dose of a Drug is 500 mg 

• Reporting threshold = 0.05%
• Identification threshold = 0.10%
• Qualification threshold = 0.15% 

 

Decision Tree for Identification and Qualification of Impurity

Rounding the Value

Quantitative results should be presented numerically, and not in general terms such as “complies”, “meets limit” etc. Any degradation product at a level greater than (>) the reporting threshold (see Attachment 1), and total degradation products observed in the relevant batches of the new drug product, should be reported with the analytical procedures indicated. Below 1.0%, the results should be reported to the number of decimal places (e.g., 0.06%) in the applicable reporting threshold; at and above 1.0%, the results should be reported to one decimal place (e.g., 1.3%).

Read also: Permitted Daily Exposure Calculation