Taking Myrbetriq to Treat Overactive Bladder

An estimated 33 million Americans live with overactive or "leaky" bladders: an uncomfortable and potentially embarrassing condition which is hard to treat. For more than three decades, there have been no new drugs to treat this condition. However, in 2012, the FDA approved Myrbetriq (mirabegron) to treat overactive bladder. 

Overactive bladder or urge incontinence refers to overactivity of the detrusor muscle. The detrusor muscle is part of the bladder wall, and when it's overactive, it contracts too much, and leakage of urine ensues. 

Overactive bladder is the most common form of urinary incontinence. Women with this condition feel an intense urge to urinate followed by uncontrollable leakage. Men experience similar symptoms, but leakage can be compromised by benign prostatic hypertrophy or urethral obstruction.

Previous Treatment Options

Before the introduction of Myrbetriq, overactive bladder was treated using pelvic floor (Kegel) exercises and biofeedback; lifestyle modification, such as weight loss or caffeine avoidance; onabotulinumtoxinA or Botox injection into the detrusor muscle; and antimuscarinic drugs such as Detrol (​tolterodine), Urotrol (oxybutynin), and solifenacin.

Antimuscarinic drugs have numerous adverse effects which make them intolerable to many people who take them. These adverse effects include dry mouth, constipation, blurred vision, and cognitive disturbance. (This toxidrome is often associated with the saying, "Blind as a bat, mad as a hatter, red as a beet, hot as Hades, dry as a bone, the bowel and bladder lose their tone, and the heart runs alone.")

Benefits of Myrbetriq

Myrbetriq is much more specific in its actions than antimuscarinic drugs usually used to treat overactive bladder. Myrbetriq also doesn't oppose the sympathetic nervous system as pervasively as antimuscarinic drugs do. Specifically, mirabegron is a beta-3 adrenergic agonist which specifically targets the receptors in the detrusor muscle (97 percent of beta-3 mRNA produced by the body is produced in the detrusor muscle).

Unlike antimuscarinic drugs, mirabegron doesn't interfere with beta-1 and beta-2 receptors in other parts of the body. In other words, whereas antimuscarinic drugs have the poor aim and affect various organ systems, mirabegron is more precise and affects mostly the bladder.

Clinical Trial Results and Side Effects

During Phase II and Phase III clinical trials, Myrbetriq was tested in more than 10,500 participants. In these studies, participants showed a decrease in the volume of urine voided, number of urgency episodes, number of incontinence episodes and number of nocturia episodes (nighttime incontinence).

Although Myrbetriq has proven much more tolerable than antimuscarinic drugs, during clinical trials, some people still experienced adverse effects including:

  • Increased blood pressure
  • Urinary tract infection
  • Abdominal pain
  • Elevated heart rate
  • Elevated blood pressure
  • Cold-like symptoms

Although increases in heart rate and blood pressure secondary to the use of Myrbetriq are modest, some experts worry about the cardiac effects of Myrbetriq. Specifically to date, there has been little research on Myrbetriq's use in adults older than 70 years old; thus, some physicians don't prescribe this drug to older patients with heart and kidney problems. Furthermore, it's still unclear whether Myrbetriq is effective when used with antimuscarinic drugs.

In August 2015, the FDA released guidance resulting from postmarketing experiences with Myrbetriq. After the drug was released to the public, some people experienced the following:

  • Nausea
  • Angioedema (swelling) of the face, tongue or larynx
  • Itchiness (pruritis)

Cases of angioedema secondary to the use of Myrbetriq could be life-threatening if the upper airway is closed off. If you experience angioedema or any other concerning symptoms after taking this medication, immediately call emergency services or seek out a physician who can help.

In addition to being more tolerable than antimuscarinic drugs in clinical trials, Myrbetriq has also proven to improve the quality of life measures among people with overactive bladder. Overall, Myrbetriq appears to be a promising new way to treat overactive bladder especially among people who can't tolerate antimuscarinic drugs. Nevertheless, more research needs to be done before we exactly understand its nuances of treatment with Myrbetriq.

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Article Sources
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