What is done in phase 1 of drug development?

• A. Large-scale efficacy trials.
• B. Animal pharmacology data are collected.
• C. Phase 1 does not involve any human subjects.
• D. Healthy volunteers are used to determine drug tolerance and toxicity; takes place after IND application.

Answer: (D)

Phase 1 focuses on safety and how the drug behaves in the body, tested in humans for the first time. It typically enrolls healthy volunteers to determine tolerance and toxicity, plus basic pharmacokinetics—how the drug is absorbed, distributed, metabolized, and excreted—and to establish a safe starting dose for later trials. This stage occurs after an IND has been filed, which allows human testing. In some cases, such as drugs with high risk or for serious illnesses, patients rather than healthy volunteers may be included. Large-scale efficacy trials happen later (phase 3) to test effectiveness, and animal pharmacology data are collected during preclinical work before any human testing. So using healthy volunteers to assess tolerance and toxicity after IND is the best fit for phase 1.