Since 1998, we have published six articles in The Medical Letter on drugs for the treatment of overactive bladder. Our next issue (1410, February 18, 2013) will include the seventh, and we are in the early stages of preparing two more. The article in our next issue includes a table that lists 13 different agents that have been approved by the FDA for this indication. Whether they are truly different is an arguable point because 12 of the 13 are anticholinergics. The 13th is mirabegron (Myrbetriq), the drug we are currently reviewing. The two medications we will be reviewing in the near future are Botox (for injection into the detrusor muscle) and an over-the-counter version of an anticholinergic patch.
Overactive bladder is a synonym for what was previously called urge incontinence, which is the most frequent cause of incontinence in the elderly. It is commonly due to overactivity (cause unknown) of the detrusor muscle, which normally empties the bladder. The symptoms of overactive bladder are urinary urgency, frequency and urge incontinence, an urgent need to void followed by leakage of urine. Anticholinergic drugs relax bladder smooth muscle, increasing the capacity of the bladder. But they don’t work very well in relieving the symptoms of overactive bladder, and they have side effects, such as dry mouth, that some patients find intolerable.
Is mirabegron any better? Can Botox paralysis of the detrusor muscle paralyze it just enough to prevent unwanted contractions, but not so much that it keeps the patient from voiding when she wants to? Hopefully, our next and future issues will answer those questions. But one thing is clear, and that is that the first line of effective therapy for this condition is not pharmaceutical, but behavioral. Timed voiding at increasing intervals, Kegel exercises to strengthen pelvic muscles, and relaxation techniques can be effective. And they are free, with no side effects. I promise we will not say that about any of the new drugs for this indication, or any other.
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The clinical studies show that this drug reduces the frequency of micturition from about 12 a day to 11 a day! That is not sufficient to call it a clinically useful drug. The placebo was almost as effective.
This is one more drug that should have stayed off market. I do not see any place of this drug in clinical practice, except as an expensive and potentially harmful placebo.