mirabegron
Brand: Myrbetriq
Prototype Drug
Drug Class: beta-3 adrenergic agonist
Drug Family: GU agent
Subclass: selective beta-3 agonist for overactive bladder
Organ Systems: reproductive
Mechanism of Action
Selectively activates beta-3 adrenergic receptors in detrusor smooth muscle, stimulating adenylyl cyclase and increasing cAMP, which relaxes the bladder muscle during the filling phase and increases bladder capacity. Unlike antimuscarinics, this mechanism does not affect bladder emptying or cause dry mouth/constipation.
beta-3 adrenergic receptor (detrusor smooth muscle)
Indications
- overactive bladder (urge incontinence, urgency, urinary frequency)
- neurogenic detrusor overactivity
Contraindications
- severe uncontrolled hypertension
- hypersensitivity
Adverse Effects
Common
- hypertension (increased blood pressure)
- nasopharyngitis
- urinary tract infections
- headache
Serious
- urinary retention (in patients with bladder outlet obstruction)
- tachycardia (QTc prolongation reported at supratherapeutic doses)
Pharmacokinetics (ADME)
| Absorption | oral bioavailability ~29–35% |
| Distribution | 71% protein bound |
| Metabolism | multiple pathways: CYP3A4, MAO, COMT, amide hydrolysis |
| Excretion | renal (55%) and fecal (34%) |
| Half-life | 50 hours |
| Onset | weeks for full effect |
| Peak | 3–4 hours |
| Duration | 24 hours |
| Protein Binding | 71% |
| Vd | 1670 L |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| digoxin | mirabegron inhibits P-gp and CYP2D6; increases digoxin levels; monitor digoxin | major |
| metoprolol | CYP2D6 inhibition increases metoprolol levels | moderate |
Nursing Considerations
- Monitor blood pressure before initiation and periodically; mirabegron raises blood pressure and is contraindicated in severe uncontrolled hypertension.
- Unlike antimuscarinics, mirabegron has no anticholinergic side effects — no dry mouth, constipation, or cognitive effects; preferred in elderly patients.
- Ensure patients have adequate bladder emptying ability; use with caution in patients with BPH or partial outlet obstruction (urinary retention risk).
- Educate patients to take consistently with or without food; full effect may take several weeks.
Clinical Pearls
- Mirabegron is the first-in-class beta-3 agonist for overactive bladder, providing an alternative mechanism to antimuscarinics (oxybutynin, tolterodine) without the troublesome anticholinergic effects that often limit adherence.
- The Beers criteria recommend antimuscarinics for OAB be avoided in elderly patients due to cognitive effects; mirabegron is increasingly preferred as the first-line OAB treatment in older adults.
Safety Profile
Pregnancy avoid
Lactation avoid
Renal Adjustment Required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.