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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Pharmacogenomics is a new field of study in medicine. It involves the identification of genetic variations that predict the response of a patient to a medication. Pharmacogenomics is relevant for all types of drugs such as medications for asthma or hypertension. It's now possible to use pharmacogenomic testing to help select an antidepressant.

In a previous blog, I discussed the relationship between a variant of the serotonin transporter gene and vulnerability to developing depression when faced with severe stress. If you have the more active form of this gene, you're less likely to develop depression even if you find yourself in a stressful situation. However, if you have the more active form of this gene and do become depressed, you're more likely to get better if you take a selective serotonin reuptake inhibitor (SSRI) antidepressant like Prozac (fluoxetine), Paxil (paroxetine), or Celexa (citalopram).

The probability of a good response to an SSRI is particularly high if you identify yourself as being "white." This suggests that other gene variations that are more common in patients of European ancestry may also influence the response of these patients to SSRI's.

For several years, it's been known that patients with the more active form of the serotonin transporter gene are more likely to respond to SSRI treatment. However, it's only been possible to test patients to see whether they have a more or less active form of this gene for the past three years. Based on the results of this pharmacogenomic testing, a psychiatrist is now able to develop a better understanding of what the probability will be for a specific patient achieving a good clinical outcome. The primary goal of testing is simply to be able to avoid side effects and identify an effective antidepressant medication more quickly.

To be able to get an even more accurate prediction of response, it will ultimately be necessary to test more than any one single gene as many genes influence the probability of responding to treatment. As testing becomes more sophisticated, there's every reason to believe that treatment outcomes will continue to improve. For many of you struggling with depression, the fact that there are now many researchers working to better understand antidepressant medication response should provide some hope.

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