What is the Origin of Zero-Order Kinetics?

This term is fundamental to pharmacology and medicinal chemistry, rooted in the mathematical modeling of drug absorption, distribution, metabolism, and excretion (ADME). The distinction between zero- and first-order kinetics is crucial for predicting drug accumulation and steady-state concentrations.

What is the Mechanism of Zero-Order Kinetics?

When the enzyme or transporter responsible for a drug's metabolism is fully saturated, such as with high-dose hormone administration, the reaction rate plateaus, and a fixed amount of the drug is eliminated per unit of time. This saturation leads to a non-linear relationship between dose and plasma concentration, meaning small dose increases can result in disproportionately large and potentially toxic increases in systemic drug levels. Understanding this kinetic profile is vital for safely titrating hormonal therapies that exhibit saturable metabolism.

Zero-Order Kinetics

Meaning

Zero-Order Kinetics is a concept in pharmacokinetics describing the elimination of a drug from the body at a constant, fixed rate, independent of the concentration of the drug present in the systemic circulation. This contrasts with the more common first-order kinetics, where the elimination rate is proportional to the drug concentration. Zero-order processes typically occur when the metabolic or transport systems responsible for drug elimination become saturated at therapeutic doses, meaning the body’s capacity to process the drug is maxed out.