Which phase of drug action focuses on the body's response to the drug?

The phase of drug action that focuses on the body's response to the drug is pharmacodynamics. This term refers to the study of how a drug affects biological systems and is concerned with the mechanisms by which drugs exert their effects, including their interactions with receptors, enzymes, and other cellular components.

In pharmacodynamics, the emphasis is on understanding the relationship between drug concentration and the resulting effect on the body, including therapeutic effects and potential side effects. This phase helps to elucidate concepts such as the dose-response relationship and the therapeutic index, ultimately guiding dosing regimens and expectations for drug efficacy.

On the other hand, the other phases — absorption, distribution, and metabolism — relate to the processes that occur before and during the transition of the drug through the body. Absorption focuses on how the drug enters the bloodstream, distribution pertains to how the drug disperses throughout the body, and metabolism involves the biochemical transformations the drug undergoes. While these processes are critical for understanding drug pharmacokinetics, they do not directly address the biological response to the drug, which is the primary concern of pharmacodynamics.