How is methadone metabolized and eliminated?

How is methadone metabolized and eliminated?

• A. Not metabolized and excreted unchanged in urine
• B. Metabolized by the liver via CYP system and eliminated via kidneys
• C. Metabolized by the kidneys and excreted in urine
• D. Metabolized by the lungs and excreted via bile

Answer: (B)

Methadone is processed mainly in the liver. It is metabolized by the cytochrome P450 enzyme system (primarily CYP3A4, with contributions from other CYPs) into inactive metabolites. These metabolites are then eliminated predominantly by the kidneys, with a portion of the drug and/or its metabolites also exiting via other routes such as feces. The key point is that hepatic metabolism drives clearance, and renal excretion handles the final elimination. The lungs are not a primary site of metabolism, and biliary excretion is not the main route for methadone.

Methadone is processed mainly in the liver. It is metabolized by the cytochrome P450 enzyme system (primarily CYP3A4, with contributions from other CYPs) into inactive metabolites. These metabolites are then eliminated predominantly by the kidneys, with a portion of the drug and/or its metabolites also exiting via other routes such as feces. The key point is that hepatic metabolism drives clearance, and renal excretion handles the final elimination. The lungs are not a primary site of metabolism, and biliary excretion is not the main route for methadone.