This month a new antidepressant came to market. Viibryd continues the trend of ever stranger new drug names (generic name vilazodone) and comes with the claim that it won’t lead to sexual dysfunction in the vast majority of users. Whether this turns out to be the case will likely determine whether Viibryd is a hugely popular new drug or just another strangely named addition to an already saturated field of SSRI type antidepressants. Viibryd is technically in a class of its own, having both serotonin reuptake properties and functioning as a post synaptic partial serotonin agonist.
The SSRI drugs prevent the reuptake of serotonin from the space between nerve endings, and lead to an increased concentration of serotonin in this space. Viibryd in addition to this function is a partial serotonin agonist. An agonist is any drug that simulates the activity of a chemical in the body. This additional function could at least in theory alter the usually side effects of an SSRI as well as alter its potential benefits.
In two relatively small studies Viibryd was found to be effective as an antidepressant, but had a very low incidence of sexual dysfunction. Specifically the incidence of orgasmic dysfunction in women and ejaculatory delay or dysfunction in men was less than 3% and very near the rates with placebo. The published rates of these side effects with all of the currently available SSRIs, including fluoxitine (Prozac), sertraline (Zoloft), paroxitine (Paxil) and others, as well as with the SNRIs like venlafaxine (Effexor) and Cymbalta are greater than 15%, and in my experience prescribing these drugs are even higher. By far the most common SSRI and venlafaxine side effects are various aspects of sexual dysfunction, especially orgasmic dysfunction. These are common enough and annoying enough that I often see patients in the office who have stopped their antidepressant medications because of their sexual dysfunction side effects.
The major factor that Viibryd is going to have to overcome is that there are several highly effective generic SSRI antidepressants on the market that are available on the discount pharmacy $4./ month offerings. As a branded antidepressant which will almost certainly be much higher priced Viibryd is going to have to show a clear benefit to gain traction in this highly competitive and saturated market. If Viibryd is found by patients and physicians to be as effective as the currently available SSRIs at treatment of depression, and really not cause orgasmic dysfunction in women and have a very low incidence of sexual dysfunction overall it is going to be a nice addition to our options for treatment of depression. I’ll reserve my judgement at this time, as prior releases of new SSRIs were touted as having lower likelyhood of these side effects. I remember the claim that Celexa side effects of sexual dysfunction were low, but in aftermarket experience Celexa (citalopram) turned out to cause only minimal if any less frequent sexual dysfunction that the SSRIs already on the market.
Viibryd is reported to have a bit higher incidence of gastrointestinal side effects than most of the SSRIs, and to avoid these side effects it is recommended that patients taper up fairly quickly in dosage. It will be interesting to see if this leads to taking an extra week or two for clinical efficacy. One of the issues we face in prescribing antidepressants in general is that they don’t work immediately, rather tend to take 2-4 weeks to start to help. Adding another week or two of ramp up in dosing may be a bit of a drawback to acceptance or Viibryd by patients. I expect the role of Viibryd to be as a second choice of an antidepressant in patients who experience bothersome sexual dysfunction on another SSRI, and Viibryd is tried as a way to avoid that problem.
Viibryd was developed by Clinical Data which was acquired by Forrest Laboratories earlier this year. Forrest also has Lexapro and Celexa as branded antidepressants, and is expected to make a big marketing push for this new product. From the surge of drug reps at my office it certainly seems like they are throwing all of their weight behind I’m anxious to see if Viibryd lives up to its marketing hype and really does work without causing sexual dysfunction. If so I expect it to be hugely successful. The market for antidepressants is huge, with Effexor and Cymbalta, two branded SNRIs having sales of over $2 billion annually. Expect the $1.1 billion Forrest paid for Clinical Data to be a bargain if Viibryd works as advertised. I plan to go slow and see how this all pans out.