In Phase I, which objective is described as Estimation of initial safety and tolerability?

• A. Pharmacokinetics
• B. Assessment of pharmacodynamics
• C. Early Measurement of Drug Activity
• D. Estimation of initial safety and tolerability

Answer: (D)

In Phase I, the primary aim is to establish safety and tolerability in humans, along with gathering basic data on how the drug behaves in the body. The phrase Estimation of initial safety and tolerability directly reflects this core purpose—to determine whether the starting doses are safe, how well patients tolerate them, and to identify any dose-limiting toxicities that guide dose escalation.

Pharmacokinetics describes how the body processes the drug (absorption, distribution, metabolism, excretion), and pharmacodynamics focuses on the drug’s effects on the body; these are important data collected in Phase I but are not the stated objective about initial safety and tolerability. Early measurement of drug activity tends to relate to early pharmacodynamic signals rather than a primary safety assessment. Therefore, the option describing initial safety and tolerability is the best fit for Phase I.