What characterizes 'zero-order kinetics'?

Zero-order kinetics is characterized by a constant elimination rate that is independent of the concentration of the drug in the plasma. This means that a fixed amount of the drug is eliminated per unit of time, regardless of how much of the drug is present in the body at any given moment. For example, if a drug is eliminated at a rate of 10 mg/hour, this rate remains the same whether the plasma concentration is high or low.

In contrast to first-order kinetics, where the rate of elimination is proportional to the concentration (higher concentrations lead to a faster rate of elimination), zero-order kinetics leads to a situation where the metabolism or clearance mechanisms of the drug become saturated. This scenario can occur with certain drugs, such as phenytoin or ethanol, at higher concentrations.

Understanding zero-order kinetics is crucial in pharmacokinetics, especially for drugs that have a narrow therapeutic window, where maintaining safe and effective drug levels is essential for therapeutic efficacy and safety.