A drug substance (DS), also referred to as active pharmaceutical ingredient (API) in the biological context, is the biologically active component of a medicinal product prior to formulation into its final dosage form. In biopharmaceutical manufacturing, drug substances include recombinant proteins, monoclonal antibodies (mAbs), viral vectors, and cell populations, and must meet defined specifications for identity, purity, potency, and safety before being processed into a drug product.
