How Myrbetriq Works for Overactive Bladder
Myrbetriq (mirabegron) treats overactive bladder (OAB) by relaxing the detrusor muscle in the bladder wall. This muscle contracts involuntarily during OAB, causing sudden urges to urinate, frequent urination, or urgency incontinence. Myrbetriq activates beta-3 adrenergic receptors on the muscle cells, increasing cyclic AMP levels. This promotes smooth muscle relaxation, allowing the bladder to hold more urine and reducing urgency and frequency.[1][2]
Mechanism Compared to Anticholinergics
Unlike anticholinergics (e.g., oxybutynin), which block acetylcholine to inhibit detrusor contractions but often cause dry mouth and constipation, Myrbetriq targets beta-3 receptors selectively. This leads to fewer cognitive side effects and better tolerability for long-term use.[1][3]
Clinical Results on Symptoms
In trials, patients taking 50 mg daily saw 1.5-2 fewer urgency episodes per day and up to 85% reduction in incontinence after 12 weeks, compared to placebo. It also increased bladder capacity by about 50 mL.[2][4]
Dosage and Administration
Start at 25 mg once daily, increasing to 50 mg after 4-8 weeks if tolerated. Swallow whole with water; no food restrictions. For kidney or liver impairment, max 25 mg.[1][5]
Common Side Effects and Risks
Hypertension (11%), urinary tract infections (6%), and headache (4%) occur most often. Monitor blood pressure before and during treatment; avoid in uncontrolled hypertension. Rare risks include urinary retention, especially with anticholinergics.[1][2]
Who Should Avoid It
Not for patients with severe liver/kidney issues, bladder outlet obstruction without catheterization, or narrow-angle glaucoma. Pregnancy category C; limited data.[1]
Sources
[1]: Myrbetriq Prescribing Information (Astellas)
[2]: FDA Label for Myrbetriq
[3]: NEJM Study on Mirabegron
[4]: European Urology Review
[5]: Drugs.com Myrbetriq Dosing