What must pharmacodynamic (PD) and pharmacokinetic (PK) assays demonstrate?

• A. They measure only chemical stability.
• B. They assess solubility and formulation.
• C. The amount and length of activity; must demonstrate activity in animals.
• D. They determine color change of indicators.

Answer: (C)

PD and PK assays focus on how much effect a drug produces and for how long, and on how the body processes the drug over time. Pharmacodynamics looks at the relationship between drug concentration and the magnitude of the effect, including how long that effect lasts. Pharmacokinetics tracks absorption, distribution, metabolism, and excretion to build a time course of drug levels in the body. Together, they define the amount of activity and its duration, often with in vivo demonstrations in animals to confirm that the drug has meaningful activity in a living system and that exposure is sufficient to drive that effect. The other options miss this purpose entirely: chemical stability, solubility/formulation, or simple color changes do not describe what PD and PK assays are meant to measure.