3.1 : 给药和治疗阶段：概述

Drugs are chemicals used for diagnosing, treating, or preventing diseases. The four phases of drug product preparation are pharmaceutic, pharmacokinetic, pharmacodynamic, and therapeutic phases.

The pharmaceutic phase focuses on the drug's physicochemical properties to design and manufacture a suitable product for effective administration. Examples include tablets or capsules for oral intake, creams or ointments for topical application, and solutions or emulsions for parenteral delivery.

Post-administration, the pharmacokinetic phase explains how the body processes the drug. It encompasses the drug's absorption, distribution, metabolism, and excretion in the body.

Upon reaching the site of action, the pharmacodynamic phase explains the drug's interaction with its target, such as receptors, ion channels, enzymes, or transporters. It helps study the relationship between the drug's concentration and its effect, whether therapeutic or toxic.

Lastly, the therapeutic phase translates pharmacological effects into clinical outcomes, that is, how the inhibition or activation of a target alleviates disease symptoms.