Antimuscarinic — Overactive Bladder Pregnancy: eMC §4.6: animal studies do not indicate direct or indirect harmful effects with respect to pregnancy, embryonal/foetal development, parturition or postnatal development. In rats, placental transfer and passage into maternal milk occur. 'For Regurin 20 mg no clinical data on exposed pregnancies are available. Caution should be exercised when prescribing to pregnant or breastfeeding women.' The US label assigns Pregnancy Category C and states there are no adequate and well-controlled studies in pregnant women.

Trospium Chloride

Brand names: Regurin, Regurin XL

Trospium chloride is an antimuscarinic agent used to treat urinary frequency, urgency and urge incontinence in adults with overactive bladder.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: One 20 mg coated tablet twice daily (equivalent to 40 mg of trospium chloride per day)

Route: Oral — 'The coated tablet should be swallowed whole with a glass of water before the meals on empty stomach'

Frequency: Twice daily

SOURCE: eMC UK SPC 'Regurin 20 mg Coated Tablets' §4.2, quoted verbatim. REVIEW: 'The need for continued treatment should be reassessed at regular intervals of 3-6 months.' PAEDIATRIC: 'Regurin is contraindicated in children aged under 12 years' (§4.2); the US label states safety and effectiveness in paediatric patients have not been established — verify any under-18 use against a children's formulary. HEPATIC IMPAIRMENT (§4.4): no data in severe hepatic impairment, so treatment of these patients is not recommended; exercise caution in mild to moderate liver impairment. US CROSS-CHECK: 'The recommended dose is 20 mg twice daily ... at least one hour before meals or given on an empty stomach'; for severe renal impairment (creatinine clearance less than 30 mL/min) 20 mg once daily at bedtime; 'In geriatric patients greater than or equal to 75 years of age, dose may be titrated down to 20 mg once daily based upon tolerability' — the UK SPC gives no separate elderly dose. §4.5 of the SPC was truncated at the source-fetch limit.

Dose adjustments

Renal

eMC §4.2: 'In patients with severe renal impairment (creatinine clearance between 10 and 30 mL/min/1.73 m2) the recommended dosage is: One coated tablet per day or every second day (equivalent to 20 mg of trospium chloride per day or every second day).' §4.4 adds that marked elevations in plasma levels have been observed in severe renal impairment and caution should also be exercised in mild to moderate renal impairment. US CROSS-CHECK: severe renal impairment (creatinine clearance less than 30 mL/min) — 20 mg once daily at bedtime.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Urinary retention
Severe gastro-intestinal condition, including toxic megacolon
Myasthenia gravis
Narrow-angle glaucoma
Tachyarrhythmia
Hypersensitivity to the active substance or to any of the excipients
Children aged under 12 years (stated in §4.2: 'Regurin is contraindicated in children aged under 12 years')
(US label additionally lists gastric retention, and specifies uncontrolled narrow-angle glaucoma, including patients at risk for these conditions)

Side effects

Dry mouth — very common; occurred in approximately 18% of trospium-treated patients versus approximately 6% on placebo in Phase III studies (US label reports 20.1%)
Dyspepsia (common) and constipation (common); abdominal pain, nausea, flatulence and diarrhoea (uncommon)
Headache (common; US label 4.2%); dizziness, and hallucination, confusion and agitation (mostly in elderly patients, facilitated by neurological disease and/or concomitant anticholinergics)
Tachycardia and tachyarrhythmia; chest pain and asthenia; vision disorders; dyspnoea
Micturition disorders and urinary retention; rash, angio-oedema, pruritus, urticaria and Stevens-Johnson syndrome / toxic epidermal necrolysis; anaphylaxis; myalgia and arthralgia; mild to moderate increase in serum transaminase levels

Interactions

Drugs with anticholinergic action (such as amantadine, tricyclic antidepressants) — potentiation of their effect
Beta-sympathomimetics — enhancement of their tachycardic action
Pro-kinetic agents (e.g. metoclopramide) — decrease in efficacy; trospium may also alter the absorption of other concurrently administered drugs through effects on gastrointestinal motility and secretion
Guar, colestyramine and colestipol — inhibition of trospium chloride absorption cannot be excluded, so simultaneous administration is not recommended
No influence on cytochrome P450 metabolic activity was observed in vitro (P450 1A2, 2A6, 2C9, 2C19, 2D6, 2E1, 3A4). US label additions: drugs eliminated by active tubular secretion (e.g. procainamide, pancuronium, morphine, vancomycin, tenofovir) may compete for this pathway and increase serum concentrations of either drug; concomitant metformin immediate-release reduced trospium exposure and peak concentration; digoxin pharmacokinetics were unaffected

Clinical monograph

How it works

It is a quaternary ammonium antimuscarinic that competitively blocks muscarinic receptors in the bladder, reducing detrusor contractions and increasing functional bladder capacity; its quaternary structure limits central nervous system penetration.

Prescribing in practice

It is contraindicated in urinary retention, significant gastrointestinal obstruction or severe gastrointestinal conditions, angle-closure glaucoma, myasthenia gravis and tachyarrhythmia.
It should be taken on an empty stomach before food, as food substantially reduces its absorption.
Caution is required in renal impairment and in older patients, with attention to overall anticholinergic burden.

Monitoring

Review symptom response after an adequate trial and monitor for anticholinergic adverse effects and urinary retention, especially in older patients.

Counselling the patient

Take the medicine before food on an empty stomach.
Report difficulty passing urine, and expect possible dry mouth and constipation.

Evidence & guidelines

Antimuscarinics are recommended by NICE for overactive bladder where conservative treatment is insufficient; see the SPC for administration advice.

Reference: NICE NG123 (Urinary Incontinence and OAB); STOPP/START v3; EAU OAB Guidelines 2024; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways