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Nuedexta: “Pipeline in a Pill” or Pipe Dream?

April 18, 2011

If you’re like me, you’ve probably seen numerous Internet ads for a new medication called Nuedexta from Avanir Pharmaceuticals.  Nuedexta was approved in October 2010 for the treatment of “pseudobulbar affect,” or PBA.  My first reaction was one of surprise, as PBA is relatively uncommon, or so I was taught: why would a drug company be aggressively advertising a drug with such a niche market?  However, as I thought about the symptoms that define PBA—and then, last week, I received a Nuedexta promotional packet in the mail—I figured I should take a look “under the hood.”

First of all, I reviewed the presentation and biology of PBA.  I remember being taught in residency that it is a fairly uncommon manifestation of neurological illness, although it has a very distinctive presentation, namely, emotional expressions that are disconnected from any subjective emotional changes.  Indeed, an alternate name for it is “pathological laughing and crying.”  Certainly, the discrepancy between a patient’s emotional display—which may be extreme, and cause great distress to caregivers—and the lack of any subjective change in mood, is highly suggestive of a focal brain abnormality.

PBA is typically caused by a specific brain lesion between the cortex (the source of voluntary thought/action) and the brainstem (the source of involuntary emotional expression like laughing and crying).  Normally, we’re stimulated to laugh or cry by something funny or sad; these emotions are first processed in the cortex, which then sends a message to the brainstem to express that emotion.  If you have a lesion between your cortex and brainstem (e.g., from a stroke, multiple sclerosis, or a degenerative process) then the emotional expression can be entirely separated from the conscious awareness of it.

Over the last decade some research groups have begun to look at dextromethorphan as a potential treatment for PBA.  Dextromethorphan, also known as DXM, is a cough suppressant, the active ingredient in Robitussin, not to mention a drug often used recreationally for its dissociative and hallucinogenic properties.  Dextromethorphan is an NMDA antagonist (i.e., it prevents glutamate from activating target cells via NMDA receptors) as well as an agonist of a type of receptor called “sigma-1,” whose role is much less understood.

When dextromethorphan is combined with quinidine, another widely available drug (used to treat heart arrhythmias), the quinidine inhibits dextromethorphan’s metabolism, allowing it to penetrate the brain at doses low enough to avoid any peripheral toxicity.  Once inside the brain, it “may act on regions implicated in emotional expression” (by an unknown mechanism) and, indeed, it improves PBA symptoms with the only significant side effects being dizziness and diarrhea.  The new drug Nuedexta is a combination of 20 mg dextromethorphan and 10 mg quinidine, and the estimated cost will be from $3000-$5000 per year.

(BTW, note the theme here, which is similar to what I wrote about with Contrave:  Nuedexta is actually a combination of two existing, generic—i.e., cheap—drugs, with a significant markup, to cover the costs of clinical testing, marketing, and, of course, shareholder profits.)

Physicians—and patients—may wonder why we need a new drug to treat PBA.  Certainly, this is a good question (although I think PBA is simply Avanir’s “foot in the door,” as I’ll discuss below).  A 2007 review in the Annals of Neurology shows that a number of medications, including SSRIs like citalopram, and tricyclic antidepressants (TCAs), are effective in managing the symptoms of PBA (see also here).  And, as I mentioned earlier, the proper diagnosis of PBA requires the presence of an underlying neurological disorder, and treatment of the disorder, too, may ameliorate the PBA symptoms.

Interestingly, while I searched for literature references discussing PBA, I found that most—if not all—of the literature from the last 5-6 years has been funded or underwritten by Avanir Pharmaceuticals—and all of which discussed the benefits of dextromethorphan/quinidine.  This included an “educational review” published by the National Stroke Association in 2005.  In fact, the editors of the Annals of Neurology issue I cited above tried to get someone to write a review on PBA but couldn’t find any authors “untouched by Avanir.”  It certainly seems that Avanir’s PR effort has paid off.

The coup de grâce, in my opinion, is an “expert review” on PBA published in the journal CNS Spectrums in October 2005.  It’s a roundtable discussion on how to distinguish PBA from other psychiatric and neurologic disorders—and, of course, the benefits of dextromethorphan/quinidine.  It seems like a fair review, although the authors make comments that broaden the definition of PBA to include other disturbances of affect, which are extremely common among psychiatric patients. “It may be useful to regard affective lability,” they write, “as a disorder of affect that exists at a point on a continuum between normal affective variability and the more severe end of the continuum characterized by [PBA].”  Furthermore, they encourage clinicians to “include a specific assessment for PBA” in all patients with any neurological condition, to prevent their being “misdiagnosed” with a psychiatric disorder—the implication being that what we might call “poststroke depression” might actually be PBA.  And they even open the door to the possibility that “PBA-like” symptoms might not have a recognizable neurological basis:  “In some cases PBA may be the only clinically identifiable manifestation of the neurological condition.  In light of the overlap between the neurology of affect regulation and the neurology of psychiatric conditions, … PBA may sometimes occur in the latter context as well.” [Emphasis mine.]

You can see where this is all headed—and probably why I received a promotional packet for Nuedexta, even though I’m not a neurologist.  Here we have a new medication, which has been approved for a neurological syndrome whose major manifestation is “affective instability.”  Even though the proper diagnosis of PBA requires far more than that, clinicians will undoubtedly use it off-label for the affective lability seen in many other conditions (such as bipolar disorder, schizophrenia, autism, dementia, maybe even childhood irritability, etc).  And my bet is that Avanir will try to get Nuedexta approved for all of these conditions.

(BTW, Nuedexta has never been compared head-to-head with SSRIs or TCAs, and the trials which led to Nuedexta’s approval showed only slight improvement vs. placebo in patients with PBA due to multiple sclerosis and ALS.)

Indeed, Avanir’s investor materials (see pdf here) already state that the company will seek approval for multiple sclerosis-related pain, and for behavioral symptoms in dementia.  And when one considers how atypical antipsychotics have been affected by “indication creep,” it is probably only a matter of time before Nuedexta will be tested for other disorders characterized by affective changes, including the big kahunas: depression and bipolar disorder.  To that end, during a November 2009 conference call to shareholders, Keith Katkin, Avanir’s CEO, described Nuedexta as a “pipeline in a pill.”

I should note here that I have not tried Nuedexta so I can’t say whether it is effective.  I also have no financial interest in Avanir Pharmaceuticals.  I don’t see how Nuedexta’s pharmacological properties might control affective outbursts (but then again, I can’t explain precisely how SSRIs treat depression, either).  Certainly I’ve read of isolated cases in which Nuedexta has led to “dramatic improvement,” but those cases are from spokespeople with “skin in the game,” so to speak.  Nuedexta might be a blockbuster drug in neurology and psychiatry alike, and I’m willing to give it that chance.  However, at this stage the marketing speaks far louder than the data, and the seeds are already being sown for the more widespread use of this relatively unproven agent.  We need to be cautious not to be swayed by the influence of those who want to make a few bucks (or a few billion) off our ignorance.

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