David Baxter PhD
Late Founder
Cytochrome P450 (CYP450) tests
Mayo Clinic
May 27, 2010
Your doctor may use cytochrome P450 tests (CYP450 tests) to help determine which antidepressant may be effective for you. Medications affect each individual differently because of inherited (genetic) traits. By checking your DNA for certain gene variations, cytochrome P450 tests can offer clues about how your body may respond to a particular antidepressant.
Cytochrome P450 tests are also being used to determine whether certain cancer medications are likely to be effective.
Cytochrome P450 tests aren't widely used yet. But cytochrome P450 tests and other genetic tests (genotyping tests) are becoming more common as doctors look for new ways to treat depression and other conditions.
Why it's done
By testing a DNA sample from your blood or skin cells, your doctor may be able to predict whether a particular antidepressant is likely to relieve your symptoms and if it's likely to cause bothersome side effects.
Medications for depression are usually prescribed based on symptoms and medical history without cytochrome P450 testing. For some people, the first antidepressant tried relieves depression symptoms and has tolerable side effects. For many others, however, finding the right medication takes trial and error. For some people, it can take several months or longer to find the right antidepressant. Genotyping tests such as cytochrome P450 tests may speed up the process of identifying the medications likely to work best.
Cytochrome P450 tests are generally used only when initial antidepressant treatment isn't successful. However, as they become more established — and new tests are developed — cytochrome P450 tests and other genotyping tests may become a standard tool used in treating depression and other conditions.
Genotyping tests also show promise for predicting risk factors for depression and a number of other conditions such as cancer and heart disease. Cytochrome P450 tests are already being used to determine whether certain cancer medications are likely to be effective.
How you prepare
You won't need to fast or undergo any special preparations prior to the procedure. You don't even have to change into a gown.
What you can expect
For cytochrome P450 tests, a sample of your DNA is taken for laboratory testing. It can be retrieved in one of two ways:
Getting a cheek swab or having a blood sample drawn should take just a few minutes, and there's virtually no risk involved. If you have blood drawn, you may have slight swelling or redness at the puncture site. Whichever type of test you have, your sample will be sent to a laboratory, where doctors will examine your DNA to look for specific genes.
Results
It usually takes several days to get the results of cytochrome P450 tests. Once they're back, you and your doctor will discuss the results and how they might affect your treatment options.
Cytochrome P450 tests are used to determine how well you process (metabolize) a drug. The results of cytochrome P450 tests divide people into four main types:
Although they have potential, genotyping tests do have limitations. Cytochrome P450 testing can't predict for certain which particular medication will work best for you — it can only provide clues. Cytochrome P450 tests only look at some of the genes involved in how your body uses certain drugs — so there are still factors involved that may affect how an antidepressant will affect you that aren't indicated by cytochrome P450 testing.
Because they're still being developed, it isn't entirely clear how useful cytochrome P450 tests are in choosing an antidepressant. An advisory group formed by the Centers for Disease Control and Prevention has concluded that there isn't enough evidence yet to support using cytochrome P450 testing for the most commonly prescribed antidepressants. But some doctors do use them and think they're helpful. Trying antidepressants based on a medical history and symptoms is still the standard method for identifying the best medication.
If you opt for testing, keep in mind that the cytochrome P450 tests aren't meant to be the only way to determine which antidepressants to try. They're just one tool that may help. Even if you have cytochrome P450 tests, you may still need to try different antidepressants and different doses to identify what works best for you.
References
Mayo Clinic
May 27, 2010
Your doctor may use cytochrome P450 tests (CYP450 tests) to help determine which antidepressant may be effective for you. Medications affect each individual differently because of inherited (genetic) traits. By checking your DNA for certain gene variations, cytochrome P450 tests can offer clues about how your body may respond to a particular antidepressant.
Cytochrome P450 tests are also being used to determine whether certain cancer medications are likely to be effective.
Cytochrome P450 tests aren't widely used yet. But cytochrome P450 tests and other genetic tests (genotyping tests) are becoming more common as doctors look for new ways to treat depression and other conditions.
Why it's done
By testing a DNA sample from your blood or skin cells, your doctor may be able to predict whether a particular antidepressant is likely to relieve your symptoms and if it's likely to cause bothersome side effects.
Medications for depression are usually prescribed based on symptoms and medical history without cytochrome P450 testing. For some people, the first antidepressant tried relieves depression symptoms and has tolerable side effects. For many others, however, finding the right medication takes trial and error. For some people, it can take several months or longer to find the right antidepressant. Genotyping tests such as cytochrome P450 tests may speed up the process of identifying the medications likely to work best.
Cytochrome P450 tests are generally used only when initial antidepressant treatment isn't successful. However, as they become more established — and new tests are developed — cytochrome P450 tests and other genotyping tests may become a standard tool used in treating depression and other conditions.
Genotyping tests also show promise for predicting risk factors for depression and a number of other conditions such as cancer and heart disease. Cytochrome P450 tests are already being used to determine whether certain cancer medications are likely to be effective.
How you prepare
You won't need to fast or undergo any special preparations prior to the procedure. You don't even have to change into a gown.
What you can expect
For cytochrome P450 tests, a sample of your DNA is taken for laboratory testing. It can be retrieved in one of two ways:
- A blood test. Blood is drawn from a vein in your arm. You may feel a slight prick when the needle is inserted.
- A cheek swab. Your doctor or other health professional will rub a cotton swab inside your cheek to retrieve a skin cell sample.
Getting a cheek swab or having a blood sample drawn should take just a few minutes, and there's virtually no risk involved. If you have blood drawn, you may have slight swelling or redness at the puncture site. Whichever type of test you have, your sample will be sent to a laboratory, where doctors will examine your DNA to look for specific genes.
Results
It usually takes several days to get the results of cytochrome P450 tests. Once they're back, you and your doctor will discuss the results and how they might affect your treatment options.
Cytochrome P450 tests are used to determine how well you process (metabolize) a drug. The results of cytochrome P450 tests divide people into four main types:
- Poor metabolizers. If you metabolize a certain drug more slowly than normal, the medication can build up in your system. This increases the likelihood that it will cause side effects.
- Normal metabolizers. If the test shows that you process certain antidepressants normally, you're more likely to benefit from treatment and to have fewer side effects than are people who don't metabolize those particular medications as well.
- Intermediate metabolizers. Because you have at least one gene involved in drug metabolism that doesn't function normally, you may not process some medications as well as normal metabolizers do.
- Ultrarapid metabolizers. In this case, medications leave your body too quickly — often before they have a chance to work properly.
- Fluoxetine (Prozac)
- Duloxetine (Cymbalta)
- Fluvoxamine (Luvox)
- Paroxetine (Paxil)
- Venlafaxine (Effexor)
- Desvenlafaxine (Pristiq)
- Nortriptyline (Pamelor)
- Amitriptyline
- Clomipramine (Anafranil)
- Desipramine (Norpramin)
- Imipramine (Tofranil)
Although they have potential, genotyping tests do have limitations. Cytochrome P450 testing can't predict for certain which particular medication will work best for you — it can only provide clues. Cytochrome P450 tests only look at some of the genes involved in how your body uses certain drugs — so there are still factors involved that may affect how an antidepressant will affect you that aren't indicated by cytochrome P450 testing.
Because they're still being developed, it isn't entirely clear how useful cytochrome P450 tests are in choosing an antidepressant. An advisory group formed by the Centers for Disease Control and Prevention has concluded that there isn't enough evidence yet to support using cytochrome P450 testing for the most commonly prescribed antidepressants. But some doctors do use them and think they're helpful. Trying antidepressants based on a medical history and symptoms is still the standard method for identifying the best medication.
If you opt for testing, keep in mind that the cytochrome P450 tests aren't meant to be the only way to determine which antidepressants to try. They're just one tool that may help. Even if you have cytochrome P450 tests, you may still need to try different antidepressants and different doses to identify what works best for you.
References
- Mrazek DA. Psychiatric pharmacogenomic testing in clinical practice. Dialogues in Clinical Neuroscience. 2010;12:69.
- Li X, et al. Clinical utility of microarrays: Current status, existing challenges and future outlook. Current Genomics. 2008;9:466.
- Zandi PP, et al. The promise and reality of pharmacogenetics in psychiatry. Psychiatry Clinics of North America. 2010;33:181.
- Black JL (expert opinion). Mayo Clinic, Rochester, Minn. May 4, 2010.
- Evaluation of genomic applications in practice and prevention (EGAPP) working group. Recommendations from the EGAPP Working Group: Testing for cytochrome P450 polymorphisms in adults with nonpsychotic depression treated with selective serotonin reuptake inhibitors. Genetics in Medicine. 2007;9:819.