Which phases of clinical trials use a subtherapeutic dose?

• A. 0, 1
• B. 0 only
• C. 1 only
• D. 0, 1, 2

Answer: (A)

Subtherapeutic dosing is about giving doses well below the level needed for a therapeutic effect to learn about a drug’s behavior with minimal risk. In phase 0, researchers use microdoses to quickly gather pharmacokinetic and pharmacodynamic data without producing noticeable therapeutic effects. In phase 1, the focus is safety and tolerability, so trials typically start at low, subtherapeutic levels and then escalate to find a safe and tolerable range while still collecting PK data. Later phases move toward therapeutic-dose exposures to test efficacy and safety, so subtherapeutic dosing isn’t the defining feature there.