Hyoscine Butylbromide

Hyoscine butylbromide is a quaternary ammonium antimuscarinic that relaxes smooth muscle of the gastrointestinal, biliary and genitourinary tracts. Its charged structure limits absorption and keeps it out of the brain, so central effects are rare, in contrast to hyoscine hydrobromide.

Classification. Antimuscarinic; antispasmodic.

Mechanism. Competitively blocks muscarinic receptors on smooth muscle and ganglia, reducing spasm, peristalsis and secretions. It also has a weak ganglion-blocking action.

Pharmacodynamics. Onset after injection within 10 minutes; after oral dosing within about 1 hour. Duration 4 to 6 hours.

Pharmacokinetics. Oral bioavailability under 1%. Half-life about 5 hours. It acts locally in the gut after oral doses and has greater systemic exposure after injection.

Metabolism. Mainly excreted unchanged in faeces after oral doses, and in urine after injection.

Adult doses unless stated.

Abdominal colic and irritable bowel syndrome (oral).

• 10 to 20 mg three to four times daily.

• Maximum 80 mg daily.

• Start at 10 mg three times daily and increase to 20 mg four times daily if needed.

Acute spasm and colic (injection).

• 20 mg by slow IV, IM or SC, repeated after 30 minutes if needed.

• Maximum 100 mg daily.

• IM injection is avoided in anticoagulated patients; use SC or IV.

Renal and biliary colic. 20 mg IV or SC alongside analgesia. An NSAID is first-line for renal colic, and antispasmodics add little.

Radiological and endoscopic procedures. 20 mg IV to reduce gut motility, with a second dose if needed.

Palliative care (bowel colic and respiratory secretions). 20 mg SC, then 60 to 120 mg over 24 hours by continuous subcutaneous infusion, with specialist advice.

Paediatric dosing.

• Oral: age 6 to 11 years 10 mg three times daily; age 12 years and over adult dose; not advised under 6 years.

• Parenteral: age under 6 years, specialist use only; 0.3 to 0.6 mg/kg with a maximum of 1.5 mg/kg daily.

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

Contraindications.

• Untreated narrow-angle glaucoma; prostatic enlargement with urinary retention.

• Mechanical gastrointestinal stenosis, paralytic ileus, megacolon.

• Tachyarrhythmias; myasthenia gravis.

• Hypersensitivity.

• IM injection in patients on anticoagulants (haematoma).

Common adverse effects. Dry mouth, blurred vision, constipation, dizziness and tachycardia.

Serious adverse effects.

• Anaphylaxis and severe hypersensitivity reactions, including after IV injection.

• Acute angle-closure glaucoma.

• Acute urinary retention.

• Tachycardia and arrhythmia, hypotension and dyspnoea with injection.

• Masking of undiagnosed severe abdominal pathology such as obstruction or appendicitis.

Major interactions.

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

• Beta-agonists: increased tachycardia.

• Metoclopramide and domperidone: prokinetic effect reduced.

• Potassium chloride tablets: increased risk of gastrointestinal ulceration.

Special groups.

• Pregnancy: limited data; avoid unless necessary.

• Breastfeeding: low transfer expected; use with caution.

• Children: restricted; avoid under 6 years orally.

• Older adults: increased risk of urinary retention, constipation and glaucoma.

• Kidney impairment: use with caution.

• Liver impairment: use with caution.

• Regional: widely available; often used without a diagnosis for abdominal pain, so exclude surgical causes first.

Formulations. Tablets 10 mg; injection 20 mg in 1 mL.

Administration.

• Swallow tablets whole with water, before meals.

• Give IV injections slowly over 1 to 2 minutes with the patient lying down.

• SC or IV is preferred over IM in patients on anticoagulants.

Baseline. Eye pressure history, urinary symptoms, heart rate and cause of abdominal pain. Exclude obstruction.

Monitoring.

• Heart rate and blood pressure after injection.

• Urinary retention and bowel function.

• Response of pain; persistent or worsening pain needs reassessment.

Therapeutic drug monitoring. Not applicable.

Stopping. No taper is needed. Stop for urinary retention, eye pain, arrhythmia or no benefit.

Referral and escalation. Urgent assessment for severe, persistent or worsening abdominal pain, fever, vomiting, distension or rectal bleeding. Eye emergency for painful red eye with halos.