To ensure the consistency of dosage units, each unit in a batch should have a drug substance content within a narrow range of the label claim. Dosage units are defined as dosage forms containing a single dose of solids (tablets, capsules, suppositories, etc.) or liquids (solutions and suspensions, etc.).

The procedure and acceptance specifications for content uniformity vary by dosage form.  Usually, a fixed number (usually 10) of dosage units (tablets, capsules, suppositories, etc.) are individually assayed for one or more API’s.  The results are compared to acceptance criteria for individual and average %Label content as well as unit to unit variation (%RSD).