A drug with zero-order kinetics is eliminated at a constant rate regardless of its concentration, meaning the elimination process is saturated. Unlike first-order kinetics, where elimination rate is proportional to drug concentration, zero-order elimination proceeds at a fixed amount per unit time. This results in a constant rate of elimination, and the half-life becomes variable and dependent on concentration. Clinical examples include phenytoin, ethanol, and aspirin at high doses, where the elimination pathways become saturated, causing drug accumulation if dosing is not adjusted.

Reference: Goodman & Gilman’s The Pharmacological Basis of Therapeutics, Brunton et al., 13th Edition.