Types of Impurities—Drug Substance

These Guidances are available on the Internet at http //www.fda.gov/cder/ guidance. In addition to the above, ICH Q6B, and Q5C are also available at the Web site, although they are not discussed here. Q6B and Q5C relate to biological and biotechnological products. 

ICH Guidance addresses impurities in drug substances to accomplish the following  

It should be noted that the methodology used for identifying and quantifying impurities is covered by another ICH guidance2 for the validation 

Q6A Specifications Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products Chemical Substances ICH 

It is therefore necessary to evaluate impurities utilizing a variety of techniques and instruments, prior to assigning purity values to the drug substance. 

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