Dicyclomine

Dicyclomine (dicycloverine) is a tertiary amine antimuscarinic that relaxes gastrointestinal smooth muscle. It is used for painful spasm in irritable bowel syndrome and functional bowel disorders. Evidence of benefit is modest, and anticholinergic adverse effects limit its use.

Classification. Antimuscarinic; antispasmodic.

Mechanism. Blocks muscarinic receptors on gut smooth muscle and also has a direct musculotropic relaxant effect. Both reduce spasm and motility.

Pharmacodynamics. Onset within 1 to 2 hours after oral dosing; effect lasts 4 to 6 hours.

Pharmacokinetics. Well absorbed orally. Peak levels at 1 to 2 hours. Half-life about 1.8 hours for the initial phase and 9 to 10 hours for the terminal phase.

Metabolism. Extensively metabolised; excreted in urine (about 80%) and faeces (about 10%).

Adult doses unless stated.

Functional bowel and irritable bowel syndrome (oral).

• Start 20 mg four times daily, before meals and at bedtime.

• After 1 week, increase to 40 mg four times daily if tolerated.

• Maximum 160 mg daily.

• Stop if there is no benefit or intolerable effects after 2 weeks at the full dose.

Intramuscular. 10 to 20 mg every 4 to 6 hours when oral use is not possible; maximum 80 mg daily; use for no more than 1 or 2 days. Never give intravenously.

Infant colic. Not used. Serious toxicity including apnoea has occurred in infants under 6 months.

Children.

• Age 2 to 11 years (specialist use): 10 mg three times daily before meals.

• Age 12 years and over: adult dose.

• Under 2 years: contraindicated.

Kidney and liver adjustment. No fixed adjustment; use with caution in impairment.

Contraindications.

• Infants under 6 months (some labels under 2 years).

• Untreated narrow-angle glaucoma; obstructive uropathy or prostatic enlargement with retention.

• Obstructive gastrointestinal disease, paralytic ileus, severe ulcerative colitis, toxic megacolon, reflux oesophagitis.

• Myasthenia gravis; unstable cardiovascular status in acute bleeding.

• Breastfeeding in some labels.

• Hypersensitivity.

Common adverse effects. Dry mouth, dizziness, blurred vision, drowsiness, nausea, constipation and nervousness.

Serious adverse effects.

• Heat stroke from reduced sweating in hot weather.

• Delirium, confusion and hallucinations, particularly in older adults.

• Urinary retention and acute angle-closure glaucoma.

• Tachycardia and arrhythmia.

• Apnoea, seizures and coma in infants.

Major interactions.

• Other anticholinergics (tricyclic antidepressants, antihistamines, antipsychotics, quinidine, disopyramide, amantadine): additive effects.

• Metoclopramide and domperidone: prokinetic effect reduced.

• Potassium chloride tablets: increased risk of gastrointestinal ulceration.

• Antacids: reduced absorption; separate by 1 hour.

• Digoxin: increased levels with slow-dissolving tablets.

Special groups.

• Pregnancy: limited data; avoid unless necessary.

• Breastfeeding: enters milk; avoid, because infants are very sensitive.

• Children: restricted; contraindicated in infants.

• Older adults: avoid where possible because of confusion, constipation and retention.

• Kidney impairment: caution.

• Liver impairment: caution.

• Regional: availability varies; check local registration.

Formulations. Tablets 10 mg and 20 mg; oral syrup 10 mg in 5 mL; injection 10 mg in 1 mL.

Administration. Take tablets 15 to 30 minutes before meals with water. Give injection deep IM only. Advise patients to avoid heat and to limit driving if drowsy.

Baseline. Eye pressure history, urinary symptoms, heart rate, and exclusion of obstruction or organic disease.

Monitoring.

• Pain and bowel pattern at 2 weeks.

• Dry mouth, urinary retention, constipation and confusion.

• Heat intolerance in hot climates.

Therapeutic drug monitoring. Not applicable.

Stopping. Taper over 1 week if used for long periods. Stop for retention, confusion, eye pain or no benefit.

Referral and escalation. Investigate red flags: weight loss, rectal bleeding, anaemia, nocturnal symptoms or new symptoms over age 50. Eye emergency for painful red eye.