Cytochrome P450 (CYP450) enzymes are a group of enzymes that are responsible for metabolizing many medications and other foreign substances in the body. These enzymes are primarily found in the liver, but can also be found in other organs such as the intestines and lungs.


CYP450 interactions occur when a medication or other substance either inhibits or induces the activity of these enzymes, which can impact the metabolism of other medications that are also metabolized by the same enzymes. There are several types of CYP450 interactions:


1. Inhibition: Some medications can inhibit the activity of CYP450 enzymes, which can lead to increased levels of other medications that are also metabolized by the same enzymes. This can increase the risk of toxicity or adverse effects. For example, fluconazole (an antifungal medication) can inhibit the activity of CYP3A4, which can increase the levels of statins (cholesterol-lowering medications) and lead to an increased risk of myopathy.


2. Induction: Other medications can induce the activity of CYP450 enzymes, which can lead to decreased levels of other medications that are also metabolized by the same enzymes. This can decrease the effectiveness of the medications and lead to treatment failure. For example, rifampin (an antibiotic) can induce the activity of CYP3A4, which can decrease the levels of some antiretroviral medications used to treat HIV.


3. Substrate: Some medications are both substrates and inhibitors or inducers of CYP450 enzymes. This means that they are metabolized by the same enzymes that they also affect. For example, carbamazepine (an anticonvulsant medication) is a substrate for CYP3A4, but also induces the activity of this enzyme, which can lead to decreased levels of other medications that are also metabolized by CYP3A4.


CYP450 interactions can occur between medications, or between medications and other substances such as herbal supplements, foods, and tobacco. It is important to consider these interactions when prescribing or taking medications, and to monitor for signs of toxicity or treatment failure when multiple medications are being used. Health care providers can use various resources to check for potential CYP450 interactions, such as drug interaction databases and clinical decision support tools.