Definition

The active pharmaceutical ingredient (API) in a drug product. CMC sections describe its manufacture, characterisation, specifications, and stability.

Example

For a small-molecule tablet, the drug substance is the chemical entity; for a monoclonal antibody, it is the purified protein.

Regulatory source

ICH Q11, ICH Q7

Common mistakes

Using non-GMP material for clinical or commercial use. Changing manufacturing process without assessing impact on quality and filing.

Inspector question

Show me the drug substance specification and how you control critical quality attributes.

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