Measurement of a drug substance is called

• A. dosage unit
• B. dosage
• C. concentration
• D. dose

Answer: (A)

The key idea is how the amount of drug is quantified in a completed dosage form. The measurement of a drug substance refers to the quantity contained in one unit of the dosage form—this is called the dosage unit. For example, a tablet that contains 500 mg of the active drug expresses that amount as the dosage unit per tablet. This is different from the dose (the amount you actually give to a patient) and from concentration (the amount per volume in a solution). It’s also not the general term dosage, which can refer more to the prescribed amount to be administered rather than the unit-level content of the product. So the term that best fits “measurement of a drug substance” is dosage unit.