Subject:
GENETICS

Short Description:
Is Pharmacogenetic Testing Used—and Useful—in Clinical Practice?

Background:

For years, we have read articles about the promise of pharmacogenetic testing to help us choose and monitor medication treatment. But relatively few psychiatrists actually use the cytochrome P450 (CYP450) genotyping tests that are available, and the last time we wrote about the topic (TCPR, August 2007), our expert opined that they added little of value to clinical decision making.

Basically, the currently available tests can tell you whether a patient will metabolize certain drugs “rapidly” or “slowly.” Presumably, one might use this data to increase or to decrease the dose, or to switch to a different drug altogether.

But how useful has genotyping been in real psychiatric settings? In a retrospective study, a Danish group reviewed the charts of all inpatients who received CYP450 testing upon admission to a mental health center between 2003 and 2009. Of 967 patients who had received the testing, 117 (12%) were found to be either “ultrarapid” or “poor” metabolizer for CYP2D6 or CYP3C19.

Most of these (101, or 86%) were actually treated with drugs metabolized by the enzyme(s) for which they had deviant results. However, this fact was noted in the chart in only about half (53) of these cases, and only 28 received “further action,” which was usually documented as “clinical observation” or “monitor drug concentration.”

The researchers observed that CYP450 testing was poorly adopted in daily clinical practice. Psychiatrists rarely actually used the test results, due to various factors: they were ordered by a different physician than the one responsible for long-term management; the results sometimes arrived after medication decisions had been made; they may have been hidden in the electronic medical record; or there were at times combined with other test results and often ignored.

The researchers didn’t elaborate on clinical outcomes, so we don’t know whether the CYP-tested patients fared better, nor whether patients receiving CYP450-dependent drugs experienced any adverse effects. The purpose of the study was strictly to describe how testing affected medical decision-making (Jürgens G et al, Acta Psychiatr Scand 2011;1–10:online ahead of print).

TCPR's Take:
The value of CYP450 genotyping in psychiatry is still in question. Even where testing is widely performed, psychiatrists rarely use the results and appear to make medication decisions the old fashioned ways—by assessing response or getting blood levels of drugs. This study was conducted on inpatients; it’s arguable that in outpatient practice the physician who ordered the test would almost surely be the same one getting the results. It is unclear from this study whether this implies that the testing has little utility or that psychiatrists need to learn how to better use the results—or some combination of the two.