CYP2D6

Overview

CYP2D6 (Cytochrome P450 2D6) is an important enzyme in the cytochrome P450 superfamily, which is involved in the metabolism of many drugs and xenobiotics in the body. It is encoded by the CYP2D6 gene located on chromosome 22q13.1. This enzyme is responsible for the oxidative metabolism of approximately 25% of all clinically used medications, including antidepressants, antipsychotics, beta-blockers, and opioids.

Function

CYP2D6 is primarily expressed in the liver, where it plays a crucial role in the metabolism of drugs. It catalyzes the oxidation of substrates by adding an oxygen atom, which often results in increased water solubility and facilitates excretion from the body. The enzyme is known for its ability to metabolize a wide variety of structurally diverse compounds, making it a key player in drug metabolism.

Genetic Variability

The CYP2D6 gene is highly polymorphic, meaning there are many different genetic variants that can affect enzyme activity. These genetic differences can lead to varying levels of enzyme activity, classifying individuals into different metabolizer phenotypes:

• Poor Metabolizers (PM): Individuals with little or no CYP2D6 function.
• Intermediate Metabolizers (IM): Individuals with reduced CYP2D6 function.
• Extensive Metabolizers (EM): Individuals with normal CYP2D6 function.
• Ultrarapid Metabolizers (UM): Individuals with multiple copies of the CYP2D6 gene, leading to increased enzyme activity.

These phenotypes can significantly influence the pharmacokinetics and pharmacodynamics of drugs metabolized by CYP2D6, affecting both efficacy and risk of adverse effects.

Clinical Significance

CYP2D6 is involved in the metabolism of several important drugs, including:

• Codeine: Metabolized to morphine, which is responsible for its analgesic effects.
• Tamoxifen: Metabolized to its active form, endoxifen, used in the treatment of breast cancer.
• Metoprolol: A beta-blocker used in the treatment of hypertension and heart failure.

The variability in CYP2D6 activity can lead to differences in drug response and toxicity. For example, poor metabolizers may experience reduced therapeutic effects or increased side effects, while ultrarapid metabolizers may require higher doses to achieve therapeutic effects.

Drug Interactions

CYP2D6 is subject to inhibition and induction by various drugs, which can lead to significant drug-drug interactions. Inhibitors of CYP2D6, such as fluoxetine and quinidine, can decrease the metabolism of CYP2D6 substrates, potentially leading to increased plasma concentrations and adverse effects. Conversely, inducers can increase the metabolism of substrates, reducing their efficacy.

Related Pages

• Cytochrome P450
• Drug metabolism
• Pharmacogenomics
• Enzyme inhibition