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Beta-3 Adrenoceptor Agonist Pregnancy: Avoid — insufficient data; animal studies suggest potential harm.

Mirabegron (Overactive Bladder — Elderly)

Brand names: Betmiga

Adult dose

Dose: 25 mg once daily initially; increase to 50 mg once daily after 4–8 weeks if tolerated
Route: Oral (modified-release tablet — swallow whole)
Frequency: Once daily
Max: 50 mg/day (standard); 25 mg/day if eGFR 15–29 or moderate hepatic impairment
First-line for OAB in elderly — preferred over anticholinergics due to absence of anticholinergic burden (no cognitive impairment, dry mouth, constipation, urinary retention). Beers Criteria 2023 and STOPP v3 recommend avoiding anticholinergics for OAB in elderly — mirabegron is the safe alternative.

Paediatric dose

Route:
Not licensed in paediatrics for OAB. Licensed for neurogenic detrusor overactivity in children ≥3 years (25 mg OD) — specialist paediatric urology only.

Dose adjustments

Renal

eGFR 15–29: maximum 25 mg once daily. eGFR <15: insufficient data — avoid.

Hepatic

Moderate hepatic impairment: maximum 25 mg once daily. Severe: avoid.

Clinical pearls

  • SCORPIO trial (Nitti et al. NEJM 2012 era): mirabegron 50 mg significantly reduced urgency incontinence episodes and voids/day vs placebo; DRAGON study confirms non-inferiority to antimuscarinic agents with superior tolerability profile
  • Anticholinergic burden and dementia: multiple systematic reviews (2019–2023) link cumulative anticholinergic exposure (including OAB antimuscarinics — oxybutynin, tolterodine, solifenacin) with increased dementia risk in elderly. MHRA 2021 update: prescribers should consider this risk. Mirabegron has no anticholinergic activity — preferred in elderly with cognitive impairment or dementia
  • Combination therapy: mirabegron can be combined with solifenacin 5 mg for refractory OAB (SYNERGY trial) — though adding anticholinergic reintroduces cognitive risk in elderly; monitor carefully

Contraindications

  • Uncontrolled hypertension (SBP ≥180 mmHg or DBP ≥110 mmHg)
  • Severe renal impairment (eGFR <15)
  • Severe hepatic impairment
  • End-stage renal disease

Side effects

  • Hypertension (modest — monitor BP, especially in elderly on antihypertensives)
  • Tachycardia (mild)
  • Urinary retention (rare — less than anticholinergics)
  • Nasopharyngitis
  • UTI
  • No clinically significant anticholinergic effects (cognitive advantage in dementia patients)

Interactions

  • CYP2D6 substrates (metoprolol, desipramine — mirabegron inhibits CYP2D6; monitor for increased levels)
  • Digoxin (mirabegron P-gp inhibitor — increases digoxin levels by 27%; monitor digoxin level after starting mirabegron)
  • Warfarin (minor increase in AUC — monitor INR after initiation)

Monitoring

  • Blood pressure (at baseline and after each dose increase — hypertension risk)
  • Heart rate
  • Digoxin levels (if co-prescribed — P-gp interaction)
  • Bladder diary (voiding frequency and urgency episodes) — efficacy assessment
  • Post-void residual (if symptoms of urinary retention)

Reference: BNFc; BNF 90; NICE CG171 (Urinary Incontinence in Women); MHRA Drug Safety Update 2021 (anticholinergic drugs and dementia); AGS Beers Criteria 2023; STOPP/START v3; MHRA SPC Betmiga. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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