Drug metabolism is the process by which the body breaks down and converts medications or other xenobiotics (foreign substances) into more easily excretable forms. This process primarily takes place in the liver, but it can also occur in other organs and tissues, such as the kidneys, intestines, and lungs. Drug metabolism is crucial for eliminating drugs from the body and reducing their potential for toxicity or side effects.

There are two main phases of drug metabolism: Phase I and Phase II reactions.

1. Phase I reactions: These reactions primarily involve the modification of the drug’s chemical structure through oxidation, reduction, or hydrolysis. The most common enzymes involved in Phase I reactions are members of the cytochrome P450 (CYP450) family. These enzymes are responsible for metabolizing a wide variety of drugs and xenobiotics. Phase I reactions often result in the formation of more polar (water-soluble) metabolites, which can be more easily excreted by the body. However, in some cases, Phase I reactions can produce reactive metabolites that may be toxic or cause adverse effects.
2. Phase II reactions: These reactions involve the conjugation of the drug or its Phase I metabolites with endogenous molecules, such as glucuronic acid, sulfate, or glutathione. Conjugation reactions typically increase the water solubility of the drug, making it easier for the body to excrete it through urine or bile. Phase II reactions are catalyzed by various transferase enzymes, such as glucuronosyltransferases (UGTs) and sulfotransferases (SULTs).

Drug metabolism can be influenced by various factors, including genetic variations, age, sex, diet, and the presence of other medications. Genetic polymorphisms in drug-metabolizing enzymes can lead to differences in drug response among individuals, which can manifest as increased susceptibility to adverse drug reactions or reduced therapeutic efficacy. Drug-drug interactions can also occur when one drug affects the metabolism of another, either by inducing or inhibiting the activity of drug-metabolizing enzymes.

Understanding drug metabolism is essential for the development of safe and effective medications, as well as for the appropriate dosing and management of drug therapies in individual patients.