Genetic Testing of Little Value in Psychiatry, Study Finds
Researchers Say Drug Metabolism Information Provides the Same Guidance
Pharmacogenetic testing provides little useful information for psychiatric prescribers, and the guidance it provides can also be gleaned from knowing how a drug is metabolized, a pair of researchers reported in the Journal of Psychiatric Practice.
Matthew Macaluso, DO, and Sheldon Preskorn, MD, of the University of Kansas Medical Center, Wichita, conducted the study involving 19 patients with major depressive disorder who did not have a good response to antidepressant treatment previously.
Each patient underwent a pharmacogenetic test. Such tests are marketed as tools which can help prescribers choose an antidepressant or antipsychotic drug and select a dosage, based on genetic factors affecting blood levels of specific medications.
The test used in the study sorts drugs into red, yellow, and green "bins." Placement is based on genes for certain enzymes which are involved in drug metabolism and how drugs are metabolized.
Of the 22 antidepressants tested, two were placed in the green bin for more than 90 percent of the patients. Eight other antidepressants were "almost never" in the green bin. Of the 16 antipsychotic drugs tested, 4 were "virtually always" in the green bin and 2 "almost never" were.
The study found that medications which are more dependent on cytochrome P450, or CYP, enzymes for their metabolism generally were classified in the yellow and red bins. Drugs metabolized by the liver and those with a "narrow therapeutic index" requiring monitoring of blood drug levels were more likely to be placed in the red bin than the yellow bin.
Drugs that were almost always in the green bin tended to be newer medications not dependent on oxidative metabolism.
"Given these results, one could predict which drugs are found in the 'green bin' more than 90 percent of the time of the time simply on the basis of knowledge of their oxidative drug metabolism without knowing the results of the patient’s genetic testing," the researchers wrote.
They suggest using information on metabolic pathways to choose an antidepressant or antipsychotic with a lower risk of variation in blood levels "may be more cost effective than genetic testing and may perhaps also be more practical."
"Pharmacogenetic testing in terms of guiding the selection of specific antidepressant and antipsychotic medications may not yet have reached the threshold of clinical utility," they added.
Macaluso M, Preskorn SH. Knowledge of the pharmacology of antidepressants and antipsychotics yields results comparable with pharmacogenetic testing. Journal of Psychiatric Practice. 2018;24(6):416-419.