Phase 2 Metabolism

Phase 2 metabolism involves conjugation - that is, the attachment of an ionised group to the drug. These groups can include glutathione, methyl or acetyl groups. These metabolic processes usually occur in the hepatocyte cytoplasm.

The attachment of an ionised group makes the metabolite more more water soluble. This facilitates excretion as well as decreasing the pharmacological activity.

Let's look at aspirin as example of a drug being metabolised. Aspirin undergoes phase 1 hydrolysis to salicylic acid. In phase 2 it is congugated with either glycine or glucoronic acid forming a range of ionised metabolytes that can then be excreted in the urine.