What is the most common action of the liver during phase II drug metabolism?

In phase II drug metabolism, the liver primarily focuses on the conjugation of substances to increase their water solubility and facilitate excretion. Glucuronidation is the most common reaction in this phase, wherein a glucuronic acid molecule is transferred to a substrate, typically drugs, hormones, or other xenobiotics.

This process occurs through the action of UDP-glucuronosyltransferases, which catalyze the transfer of glucuronic acid from the cofactor UDP-glucuronic acid to the target. The result is a more polar compound that is less pharmacologically active and can be readily excreted by the kidneys or through bile. This conjugation significantly enhances the elimination of lipophilic drugs from the body, reducing their potential toxicity.

While other reactions exist in phase II metabolism, such as sulfation and methylation, glucuronidation is the predominant pathway due to its efficiency and the broad range of substrates it can accommodate. This makes it a crucial process in the liver's role in drug metabolism and clearance.