Drug Action and Pharmacokinetics Overview

Study Notes

A successful drug is composed of three key factors: activity, **ADME (Absorption, Distribution, Metabolism, Excretion) **, and safety (Toxicity).
The pharmaceutical phase of drug action involves the disintegration of a pill's components in the gastrointestinal tract (GIT), followed by the release and dissolution of the drug.
The pharmacokinetic phase is the study of how the body absorbs, distributes, metabolizes, and eliminates a drug (ADME).
The pharmacodynamic phase explores how a drug interacts with its specific biological target at a molecular level and the subsequent pharmacological effects that result.

The most effective drug for binding interactions isn't necessarily the most successful drug in medicine.
A drug reaching its target is crucial for effectiveness, therefore the study of pharmacokinetic and pharmacodynamic phases is vital.

Drug dissolution is influenced by the pH of the medium.
Weakly acidic drugs dissolve better in alkaline regions of the GIT and vice versa.

Drug absorption includes the passage of the drug from the GIT into the bloodstream.
Passive diffusion.
- Para- and transcellular are passive processes and dominate (~90% of drug absorption).
- Transcellular: occurs through the cell membrane or cytoplasm, relatively fast, and may occur throughout the GIT wall.
  - Lipid-soluble unionized drugs dissolve in the membrane and are driven through by a concentration gradient.
- Paracellular: occurs through aqueous pores between cells, slower, and is mainly present in the small intestine.
  - Primarily for polar, small molecules.
Carrier-mediated facilitated transport is typically seen with some polar drugs, commonly those similar to endogenous compounds that rely on specific membrane carrier systems (e.g., methotrexate).
Ionization plays a role in drug absorption.