Learning Objective

Understand the processes and routes of drug elimination, the concept of elimination half-life (t₁/₂), and the kinetic principles that govern drug clearance from the body.

Elimination

Elimination is the process by which drugs are removed from the body, either from plasma or tissues, and includes both metabolism and excretion.

Major Modes of Elimination

1. Biotransformation (metabolism): Conversion of active drugs into inactive or more water-soluble metabolites, usually via Phase I and Phase II reactions.
2. Renal excretion: Drugs and metabolites are excreted via the kidneys.
3. Other excretory pathways include bile, lungs, and sweat.

Elimination Half-Life (t₁/₂)

1. The time required to reduce the plasma concentration of a drug by 50%.
2. Important for:
   1. Determining dosing intervals
   2. Predicting time to steady-state
   3. Understanding the duration of drug action