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.
- Starting: 25 mg once daily
- Maximum: 50 mg once daily
- Mirabegron may be taken without regard to food
- It may take up to 8 weeks for a noticeable effect
Efficacy: The manufacturer's package insert cites three 12-week studies.
- In those studies, the following effects were seen:
- Mirabegron decreased the number of incontinence episodes per 24 hours by 0.34 - 0.42 when compared to placebo
- Mirabegron decreased the number of urinations per 24 hours by 0.42 - 0.61 when compared to placebo
- Mirabegron increased the volume of urine voided per urination by 4.6 - 12.4 ml when compared to placebo
| Side effects of Myrbetriq in Placebo-controlled trials |
| Side effect |
Placebo
(N=1380) |
Myr 25 mg
(N=432) |
Myr 50 mg
(N=1375) |
| 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:
- Increase in blood pressure - mirabegron may increase blood pressure in some individuals. In studies, the mean maximum increase in systolic/diastolic blood pressure
was approximately 3.5/1.5 mmHg greater than placebo in patients taking 50 mg.
- Urinary retention - may occur in patients with bladder obstruction and/or in patients taking anticholinergics
- Angioedema - cases of angioedema have been reported in patients taking mirabegron
- Kidney disease - dose should not exceed 25 mg/day in patients with a CrCl of 15 - 29 ml/min. Do not use in patients with CrCl < 15 ml/min.
- Liver disease - dose should not exceed 25 mg/day in patients with Child-Pugh Class B liver disease. Do not use in patients with Child-Pugh Class C.
Drug interactions:
- Mirabegron is a moderate CYP2D6 inhibitor. Dosage adjustments may be necessary when it is taken with CYP2D6 substrates.
- Mirabegron may increase digoxin levels
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]
