Which hepatic metabolism phase is responsible for conjugation of drugs?

• A. Phase III
• B. Phase II
• C. Phase I
• D. Phase IV

Answer: (B)

Conjugation in the liver is Phase II metabolism. After a drug has often been modified by Phase I to introduce or expose a functional group, Phase II ties the drug to an endogenous molecule such as glucuronic acid, sulfate, glycine, acetyl groups, or glutathione. This attachment greatly increases the molecule’s polarity, making it much more water-soluble and easier to eliminate in urine or bile. Enzymes like UDP-glucuronosyltransferases, sulfotransferases, and glutathione S-transferases carry out these reactions, usually in the liver’s cytosol or smooth endoplasmic reticulum. While many Phase II metabolites are inactive, some can be active or reactivated later in the body, but the overall effect is to facilitate detoxification and clearance.