Antispasmodic Drugs

Antispasmodic drugs relax gut smooth muscle by blocking muscarinic receptors, calcium channels or smooth muscle directly. They relieve cramping pain in irritable bowel syndrome, biliary and intestinal colic and during endoscopy.

Classification. Antimuscarinic (hyoscine butylbromide, dicycloverine), direct smooth muscle relaxants (mebeverine, alverine, drotaverine), calcium channel blockers (pinaverium, otilonium), and peppermint oil.

• Hyoscine butylbromide 20 mg orally four times daily (maximum 80 mg daily); 20 mg intramuscularly or intravenously, repeated after 30 minutes; maximum 100 mg daily by injection.
• Mebeverine 135 mg three times daily, 20 minutes before meals.
• Dicycloverine 10 to 20 mg three times daily; maximum 160 mg daily.
• Alverine citrate 60 to 120 mg three times daily.
• Drotaverine 40 to 80 mg two to three times daily.
• Peppermint oil 0.2 to 0.4 mL capsules three times daily before meals.

Differences. Antimuscarinic agents cause anticholinergic effects; the direct relaxants and peppermint oil do not.

• Irritable bowel syndrome: after diet and lifestyle measures, an antispasmodic as needed for pain; review at 4 weeks and stop if no benefit.
• Biliary and intestinal colic: hyoscine butylbromide adjunct to analgesia.
• Renal colic: an NSAID is better; antispasmodics add little.
• Endoscopy and imaging: hyoscine butylbromide 20 mg intravenously to reduce peristalsis.

Contraindications. Intestinal obstruction, paralytic ileus, megacolon, narrow-angle glaucoma, myasthenia gravis, urinary retention, tachyarrhythmia (antimuscarinics). Peppermint oil in severe reflux or hiatus hernia.

Adverse effects. Dry mouth, constipation, blurred vision, urinary retention, tachycardia. Peppermint oil: heartburn and perianal burning.

Interactions. Additive anticholinergic effects with tricyclic antidepressants, antihistamines and antipsychotics. Antimuscarinics oppose metoclopramide.

Special groups.

• Pregnancy: limited data; use only when needed.
• Breastfeeding: limited data.
• Children: age-specific dosing only; avoid peppermint oil under 8 years.
• Older adults: avoid antimuscarinics (delirium, retention).
• Kidney and liver impairment: caution.

Monitoring. Symptom response, bladder emptying, heart rate and mental state.

Referral and escalation. Onset over 50 years, rectal bleeding, weight loss, anaemia, nocturnal symptoms, abnormal calprotectin or a family history of bowel cancer needs investigation, not symptomatic treatment.