M3-Selective Antimuscarinic — Overactive Bladder
Pregnancy: Avoid in pregnancy
Darifenacin
Brand names: Emselex
Adult dose
Dose: 7.5 mg once daily; increase to 15 mg after 2 weeks if needed
Route: Oral
Frequency: Once daily (with or without food)
Max: 15 mg/day
M3-selective: theoretical advantage in reduced cardiac (M2-mediated) effects; less tachycardia vs non-selective antimuscarinics
Paediatric dose
Dose: Not applicable N/A/kg
Route: Oral
Frequency: Not applicable
Max: Not applicable
Not licensed in children
Dose adjustments
Renal
No dose adjustment required
Hepatic
Max 7.5 mg/day in moderate hepatic impairment; avoid in severe
Paediatric weight-based calculator
Not licensed in children
Clinical pearls
- M3-selective: targets the primary receptor subtype responsible for detrusor contraction — theoretical advantage is less tachycardia (M2-mediated effect) but no major clinical superiority demonstrated over non-selective agents in head-to-head trials
- Constipation is notably higher than some other OAB agents due to high M3 selectivity in GI tract — consider laxative in elderly or constipation-prone patients
- CYP3A4 metabolism: significant interaction with azole antifungals and macrolide antibiotics — common combinations in elderly; cap dose at 7.5 mg if on these agents
- Once-daily dosing with modified-release formulation aids adherence — useful in complex medication regimens
- NICE NG123: Patient preference and tolerability should guide antimuscarinic choice — no clear superiority between agents
Contraindications
- Urinary retention
- Gastric retention
- Uncontrolled narrow-angle glaucoma
- Myasthenia gravis
Side effects
- Dry mouth (very common)
- Constipation (common — higher than non-selective antimuscarinics due to M3 selectivity in gut)
- Headache
- Dyspepsia
- Urinary retention
Interactions
- Strong CYP3A4 inhibitors (ketoconazole, clarithromycin — increase darifenacin levels; max 7.5 mg/day)
- CYP2D6 inhibitors (fluoxetine, paroxetine — modest increase)
- Other antimuscarinics (additive effects)
Monitoring
- OAB symptom scores
- Post-void residual
- Bowel function (constipation)
Reference: BNFc; BNF 90; NICE NG123 (Urinary Incontinence and OAB); EAU OAB Guidelines 2024. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators