FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam 2026 - Free NABP Practice Questions and Study Guide

Drugs that exhibit zero-order kinetics are characterized by a constant amount of the drug being eliminated from the body per unit of time, regardless of its concentration. Theophylline is a prime example because at therapeutic and high concentrations, its elimination can become saturated. This means that when the drug levels exceed a certain point, the liver enzymes responsible for its metabolism become overwhelmed, leading to a fixed rate of elimination rather than a rate that varies with concentration. This saturation is a hallmark of zero-order pharmacokinetics.

In contrast, the other drugs listed typically follow first-order kinetics, where the rate of elimination is proportional to the drug concentration. For instance, ibuprofen, acetaminophen, and amoxicillin all show elimination rates that vary with their concentrations in the bloodstream, meaning that higher concentrations will lead to a faster rate of elimination, which distinguishes them from theophylline in this context. Therefore, theophylline is correctly identified as the example of a drug that follows zero-order kinetics.