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

Xenobiotics are characterized as chemicals that are foreign to the body. This term encompasses a wide range of substances, including pharmaceuticals, environmental pollutants, and food additives, among others. The fundamental aspect of xenobiotics is that they are not naturally produced or expected components of the human biological system, which distinguishes them from endogenous substances.

Understanding the context of drug metabolism is essential. When xenobiotics enter the body, they can undergo various metabolic processes to ensure they are safely eliminated. This often involves two phases: Phase I reactions, which introduce or expose functional groups, and Phase II reactions, which typically involve conjugation and lead to more water-soluble metabolites that can be easily excreted.

The other choices provide relevant information but do not correctly define xenobiotics. Compounds metabolized in the liver and those eliminated through phase II reactions can include both xenobiotics and endogenous substances. Natural substances produced by the body clearly fall outside the definition of xenobiotics, as they are not foreign compounds. Thus, the correct characterization of xenobiotics as chemicals foreign to the body underscores their importance in pharmacology and toxicology.