New antidepressant offers hope

For those of you with depression who've been struggling to find the right antidepressant medication, the introduction of a new antidepressant is always a hopeful event. Recently, the antidepressant vilazodone became available to U.S. patients. The trade name of this new medication is Viibryd.

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The mechanism action of vilazodone is somewhat different from many antidepressants. While vilazodone does inhibit the reuptake of serotonin like so many other antidepressants, it's also a "partial agonist" of the serotonin 1A receptor. This second mechanism may be particularly helpful for some people based on the receptivity of their serotonin 1A receptor.

It's not clear who will be most likely to respond well to vilazodone as a result of its effect on the serotonin 1A receptor. However, future research focusing on differential response may well lead to clues that will help us identify who will respond to vilazodone.

The metabolic profile of vilazodone makes it quite likely that most people will be able to tolerate it at the recommended dose. However, since vilazodone is metabolized by the cytochrome P450 3A4 enzyme, a small number of people who have deficient copies of the gene that codes for this enzyme are unlikely to tolerate vilazodone at the standard dose. This problem with tolerance will also be true for people who have a normal metabolic capacity, but who take medications that inhibit the function of the 3A4 enzyme.

One of the most attractive aspects of this newly released antidepressant is that the initial clinical trials reported a quite low incidence of sexual side effects. If these initial reports are confirmed as larger numbers of people are treated, vilazodone will clearly become the antidepressant of choice for those who have struggled with sexual side effects while taking either the SSRI's or the SNRI's.

At this point, there's been little pharmacogenomic research focused on this new drug. However, as individualized molecular psychiatry becomes more prominently practiced, future research will hopefully provide some clues as to which of you will be most likely to respond to vilazodone.

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