Recently, the FDA approved the Amplichip CYP450 Test (from Roche Diagnostics), which is a device allowing laboratories to quickly find out whether your patient metabolizes drugs too slowly or too quickly. Theoretically, poor metabo- lizers (PMs) should be given lower doses of P450-metabolized SSRIs, such as Prozac and Paxil, whereas ultra-rapid metabolizers should be given higher-than-normal doses.
Recently, the Centers for Disease Control funded researchers to review the literature on this issue. The final 145-page report concluded that P450 testing is definitely not ready for prime-time. Mostof the studies have relied on giving healthy volunteers a single dose of an SSRI in order to measure the effect of P450 genotype status on serum levels. Studies of depressed populations, however, have led to wildly inconsistent results, and no firm conclu- sions can be drawn.
By far the best way to prescribe SSRIs, according to the team, is to choose an agent that is not significantly metabolized by the P450 system, which would include Celexa, Lexapro, or Zoloft (Download report from http://www.ahrq.gov/clinic/tp/cyp450tp.htm).
TCPR’s Take: It’s hard to argue with the report’s conclusions. In general, it’s reasonable to restrict P450 testing to our “challenging” patients, such as those who have not responded to multiple medica- tions or those who report intolerable side effects to miniscule doses.
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