3.22 : Drug Elimination: The Concept of Clearance

Drug elimination refers to removing drugs from the body, either through urine by the kidneys or through bile by the liver. Drug clearance is a pharmacokinetic parameter that measures the efficiency of drug removal from the bloodstream within a specific time frame. It is calculated as the rate at which a drug is eliminated from plasma divided by the plasma concentration of the drug.

Drug clearance is not limited to renal excretion but encompasses all organs involved in drug elimination, including the liver, lungs, and biliary system. The sum of clearances by all eliminating organs is known as the total body or systemic clearance. It can be expressed as a combination of renal clearance and nonrenal clearance.

Understanding drug elimination kinetics and the concept of drug clearance is essential for designing effective dosage regimens and ensuring safe and optimal drug therapy. It allows for individualized adjustments based on a person's specific needs.

Exceeding the prescribed dosing rate can overload elimination pathways and decrease drug clearance. This leads to elevated plasma drug concentrations, which can result in toxic levels and cause adverse effects.