Scopolamine - Drug Monograph

Introduction

Scopolamine, also known as hyoscine, is a tropane alkaloid derived from plants of the Solanaceae family (nightshade plants). It is a muscarinic antagonist that has been used medically for over a century. Scopolamine is most commonly recognized for its transdermal delivery system used to prevent motion sickness, but it has several other important clinical applications.

Mechanism of Action

Scopolamine acts as a competitive antagonist at muscarinic acetylcholine receptors (primarily M1-M5 subtypes) in the central and peripheral nervous systems. By blocking acetylcholine binding, it inhibits parasympathetic nervous system activity. Its antiemetic effects are mediated through action on the vestibular nuclei and higher CNS centers, including the vomiting center. The drug also affects the iris and ciliary muscle of the eye (causing mydriasis and cycloplegia) and reduces various secretory glands.

Indications

• Prevention of nausea and vomiting associated with motion sickness
• Prevention of postoperative nausea and vomiting (PONV)
• Management of sialorrhea (excessive salivation)
• Gastrointestinal spasms (oral formulation in some countries)
• Pre-anesthetic medication to reduce secretions
• Cycloplegic and mydriatic for ocular examinations

Dosage and Administration

• Apply one patch to hairless area behind ear 4 hours before anticipated need
• Each patch delivers approximately 1 mg over 3 days
• Replace every 72 hours if needed

• Transdermal: Apply patch the evening before surgery or 1 hour before cesarean section
• IV/IM: 0.3-0.6 mg administered preoperatively

• Renal impairment: Use with caution; consider reduced dosing
• Hepatic impairment: Use with caution
• Geriatric: May require dose reduction due to increased sensitivity
• Pediatric: Safety not established for transdermal system in children

Pharmacokinetics

Contraindications

• Hypersensitivity to scopolamine or any component of formulation
• Angle-closure glaucoma
• Gastrointestinal or genitourinary obstruction
• Myasthenia gravis
• Children under 12 years (transdermal system)

Warnings and Precautions

• May cause drowsiness and blurred vision; caution when operating machinery
• Risk of withdrawal symptoms after discontinuation of prolonged use
• Use with caution in patients with:

- Prostatic hyperplasia - Seizure disorders - Cardiac arrhythmias - Hepatic or renal impairment - Elderly patients (increased risk of confusion, hallucinations)

• Avoid contact with eyes (may cause pupil dilation)
• Remove patch before MRI procedures (contains aluminum)

Drug Interactions

• CNS depressants: Enhanced sedative effects (alcohol, benzodiazepines, opioids)
• Anticholinergic agents: Additive effects (antihistamines, tricyclic antidepressants, antipsychotics)
• Cholinergic agents: Antagonizes effects of bethanechol, donepezil
• Metoclopramide: May antagonize prokinetic effects
• Ketoconazole: May increase scopolamine concentrations

Adverse Effects

• Dry mouth (67%)
• Drowsiness (≤50%)
• Blurred vision
• Dizziness

• Confusion (especially in elderly)
• Hallucinations
• Photophobia
• Urinary retention
• Tachycardia
• Rash at application site
• Withdrawal symptoms (nausea, vomiting, dizziness) after discontinuation

Monitoring Parameters

• Visual acuity changes
• Mental status changes (especially in elderly)
• Heart rate and rhythm in susceptible patients
• Urinary function in patients with prostatic hyperplasia
• Signs of hypersensitivity reactions
• Withdrawal symptoms after discontinuation

Patient Education

• Apply patch to clean, dry, intact skin behind ear
• Wash hands thoroughly after handling patch
• Avoid touching eyes after handling patch
• Do not cut patches
• May cause drowsiness; avoid alcohol and driving until effects known
• Remove patch and contact provider if vision changes, confusion, or eye pain occur
• If patch becomes dislodged, discard and apply new patch to different site
• Proper disposal: Fold used patch with adhesive sides together

References

1. Nachum Z, Shupak A, Gordon CR. Transdermal scopolamine for prevention of motion sickness: clinical pharmacokinetics and therapeutic applications. Clin Pharmacokinet. 2006;45(6):543-566. 2. Kranke P, Morin AM, Roewer N, Eberhart LH. Dimenhydrinate for prophylaxis of postoperative nausea and vomiting: a meta-analysis of randomized controlled trials. Acta Anaesthesiol Scand. 2002;46(3):238-244. 3. Product Monograph: Transderm Scopolamine. Novartis Pharmaceuticals. 4. American Society of Health-System Pharmacists. AHFS Drug Information. Bethesda, MD: ASHP. 5. Sweis I, Kamen J, Biller W, et al. A prospective randomized controlled trial of transdermal scopolamine for the prevention of postoperative nausea and vomiting. Front Pharmacol. 2019;10:285. 6. Bailey PL, Pace NL, Ashburn MA, et al. Frequent hypoxemia and apnea after sedation with midazolam and fentanyl. Anesthesiology. 1990;73(5):826-830.