Medication Selection and the Genetic Test for Psychiatric Medications: The Promised Land of Pharmacogenomics
There is a new fad that hit the shelves of online retailers a few months ago. Cheek-swab kits that promise to determine which psychiatric medication will work for you have become all the rage. Such tests exist, but they are not without some very important caveats. Many are being ‘oversold’ by online retailers, and their use can pose significant problems for individuals. There is valid information that can be provided by pharmacogenomic (PGx) testing, but some promises that are currently touted by companies selling these tests is simply not supported by the current evidence.
What Pharmacogenomic Testing Actually Measures
Psychotropic medications are primarily metabolized in the liver by a family of enzymes called the cytochrome P450 (CYP450) enzymes. Specific genes like CYP2D6 and CYP2C19 determine the rate of a person’s liver metabolism of certain medications. Therefore, a cheek swab or a blood draw can test for specific genetic variations in these genes to determine a person’s status as a poor, intermediate, normal, rapid, or ultrarapid metabolizer.
Poor metabolizers are at increased risk of adverse drug reactions caused by drug accumulation. The clear the drug from their system more slowly. Conversely, ultrarapid metabolizers are at increased risk of treatment failure due to rapid drug metabolism and resultant low drug concentrations. They clear the drug from their system very quickly. Therefore, by identifying an individual’s metabolic status, PGx testing can potentially help to predict and prevent adverse drug reactions and improve treatment outcomes by suggesting optimal drug dosages.
Where the Marketing Gets Ahead of the Science
While there is modest evidence to support the prediction of treatment outcomes, there is far less supporting the prediction of efficacy (i.e., does the new drug work?!). While many PGx tests include a comprehensive listing of known drug-gene interactions, many are not particularly good at predicting metabolism. And yes, there are some issues with known gene-drug interactions (e.g. HLA-B*1502 and carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis). Examples of these interactions are often used in marketing of these commercial panels.
A test indicating that a particular antidepressant is OK for a patient to take based on how they metabolize the drug does not guarantee that the drug will work in treating their depression. A positive PGxtest for a medication is just another piece of information which can be combined with other pieces of information such as a patient’s full medication history, their full psychiatric symptom history, their sensitivity to side effects, and their full medical history and that of their blood relatives.
Who Actually Benefits From Testing
At Pima Behavioral Health, we feel, in most cases, that the biggest value in PGx testing is in patients who have tried two or more antidepressants with no benefit, who have had unusual or even severe side effects at very low doses, and whose families have a history of very unusual reactions to certain types of psychiatric medications. This is not typically the average patient beginning treatment with their first antidepressant. Most psychiatric treatment begins with straightforward medication choices based on clinical diagnosis and history, and then changed based on response (or lack of response) to treatment.
Costs for these tests vary widely and are sometimes not covered by your insurance plan. Thus, they can cost several hundred dollars out of pocket. It is always best to first ask your murse practitioner if, based on your individual case, or treatment plan, the test would likely to add anything of value or simply confirm what your nurse practitioner would have chosen based on your individual case.
How We Actually Use the Results
At Pima Behavioral Health, we use the PGx test results as one piece of information in the patient’s overall care plan. We look at the results of your genetic test in correlation with the medications that have already been used, known drug interactions, and treat you accordingly. In some cases, the test results can confirm what we were already suspecting. In other cases, the results point to another treatment option that may not have been considered before. Either way, when appropriate, we utilize the test results to help guide our treatment decisions in your care.
When to Reach Out
Whether a medication trial will work for you or not is something that can be discussed with your nurse practitioner. He or she will look at the results of your PGx testing and look at your full clinical picture to determine whether the results of the test will be useful for you. Pima Behavioral Health serves Tucson, Arizona and surrounding areas and can be reached at 520-355-1122 or through our website at www.pimabh.com. Contact us today to schedule an evaluation to discuss your medication options to help get you back to the best version of you!