Knowledge of the Pharmacology of Antidepressants and Antipsychotics Yields Results Comparable With Pharmacogenetic Testing

Several companies offer pharmacogenetic testing for psychiatry on the basis of the claim that the outcome of drug selection is better when guided by such testing than when such testing is not used. This column examines the results of the GeneSight Psychotropic Test which groups various antidepressants and antipsychotics into 3 bins: green (use as directed), yellow (use with caution), and red (use with increased caution and more frequent monitoring). The authors examined how frequently the same drugs appeared in these different bins in 19 patients. They found that of the 22 antidepressants evaluated, 2 were virtually always (>90%) in the green bin: desvenlafaxine and levomilnacipran; and 8 were almost never (10.5%) in the green bin: citalopram, duloxetine, escitalopram, fluoxetine, fluvoxamine, mirtazapine, paroxetine, and sertraline. Of the 16 antipsychotics evaluated, they found that 4 were virtually always (>90%) in the green bin: asenapine, lurasidone, paliperidone, and ziprasidone; and 2 were almost never (10.5%) in the green bin: chlorpromazine and thioridazine. What was common among those drugs almost always in the green bin versus those almost never in the green bin were newer versus older marketed drugs and those not dependent versus dependent on oxidative metabolism for their clearance. The authors concluded that the results of this pharmacogenetic testing could be predicted on the basis of knowledge of the pharmacology of the drugs, particularly whether their clearance was dependent on oxidative drug metabolism.