2025 CARN Practice Exam – Comprehensive Study Guide

Methadone is primarily metabolized in the liver, making it the correct choice. The liver plays a crucial role in drug metabolism due to its rich supply of enzymes involved in the biotransformation of various substances. Specifically, methadone undergoes extensive hepatic metabolism through cytochrome P450 enzymes, particularly CYP3A4, CYP2B6, and CYP2C19. The metabolites produced are less active or inactive and are typically excreted from the body via the kidneys.

Understanding this metabolic pathway is significant for healthcare professionals, especially those working with patients undergoing opioid replacement therapy, as liver function can affect methadone levels in the blood. This knowledge is vital for dosing and managing potential interactions with other medications that may also be metabolized in the liver.

The other options do not play a primary role in the metabolism of methadone. Kidneys are more involved in the excretion of metabolites rather than metabolism itself, while the pancreas and lungs do not participate in the metabolic processes of methadone.