Background: Overactive bladder is a condition where the bladder muscle contracts involuntarily. Overactive bladder can lead to urine leakage, urgency to urinate, and frequent urination. Overactive bladder is typically treated with a class of drugs called anticholinergics (e.g. Detrol®, Ditropan®, Vesicare®, and Enablex®). Mirabegron is part of a new class of drugs for overactive bladder that work different from anticholinergics. Mirabegron was FDA-approved in 2012, and a second addition to the class, vibegron (Gemtesa®), was approved in 2020.

Mechanism: Mirabegron (Myrbetriq®) stimulates beta-3 adrenergic receptors in the bladder muscle wall which causes the bladder to relax

Dosage: Mirabegron (Myrbetriq®) is available as a 25 and 50 mg extended-release tablet.

Efficacy: The manufacturer's package insert cites three 12-week studies.

Side effects of Myrbetriq in Placebo-controlled trials
Side effect Placebo
Myr 25 mg
Myr 50 mg
Hypertension 7.6% 11.3% 7.5%
Nasopharyngitis 2.5% 3.5% 3.9%
Urinary Tract Infection 1.8% 4.2% 2.9%
Headache 3.0% 2.1% 3.2%
Constipation 1.4% 1.6% 1.6%
Upper Respiratory Tract Infection 1.7% 2.1% 1.5%
Arthralgia 1.1% 1.6% 1.3%
Diarrhea 1.3% 1.2% 1.5%
Tachycardia 0.6% 1.6% 1.2%
Abdominal Pain 0.7% 1.4% 0.6%
Fatigue 1.0% 1.4% 1.2%

Contraindications / Precautions:

Drug interactions:

Summary: Mirabegron has a unique mechanism that differs from the widely used anticholinergic drugs. Based on the studies presented in the package insert, its effects appear to be modest. Blood pressure increases are a worrisome side effect. A second beta-3 adrenergic receptor agonist, vibegron (Gemtesa®), was approved in 2020. Vibegron did not appear to raise blood pressure in pre-marketing studies. [Myrbetriq PI] [Gemtesa PI]