Scopolamine
Scopolamine
Generic Name
Scopolamine
Mechanism
- Competitive antagonist at *muscarinic acetylcholine receptors* (M1‑M5).
- Inhibits parasympathetic neurotransmission in the vestibular system, decreasing nausea signals.
- Attenuates secretomotor activity of the gastrointestinal tract, reducing nausea/vomiting frequency.
- Because of central nervous system penetration, it also reduces smooth‑muscle contractions in the gut and the oculomotor pathways responsible for motion‑induced vertigo.
Pharmacokinetics
| Parameter | Typical Value | Notes |
| Absorption | Oral: 25–45 % bioavailability. Transdermal patch: ~1 mg/patch/day (0.7 mg released). | Patch is the preferred route for motion sickness due to steady release and minimal first‑pass metabolism. |
| Distribution | Volume of distribution ≈ 8 L/kg. Highly protein‑binding (~80 %). | Penetrates CNS and retinal tissues. |
| Metabolism | Hepatic via sulfation and glucuronidation. | Minimal CYP450 involvement. |
| Elimination | Renal clearance; half‑life 3–8 h (oral). Patch: steady state by 24–48 h. | Dose adjustments: none for mild‑moderate renal impairment; cautious in severe renal disease. |
| Onset/Duration | Patch: 30–120 min onset; effect lasts 24–48 h. Oral: 1–2 h onset; effect 4–6 h. | Transdermal provides sustained coverage for prolonged travel. |
Indications
- Pre‑operative / Post‑operative nausea and vomiting (PONV) prophylaxis.
- Motion sickness (sea, air, automotive).
- Vestibular vertigo (e.g., benign paroxysmal positional vertigo).
- Pre‑operative anxiolysis (limited evidence).
- Pre‑operative sedation in selected cases.
Contraindications
- Known hypersensitivity to scopolamine, hyoscine, or related tropane alkaloids.
- Glaucoma (especially narrow‑angle), myasthenia gravis, acute urinary retention, prostatic hypertrophy.
- Severe cardiovascular disease (tachycardia, advanced AV block) – significant antimuscarinic effect can worsen arrhythmias.
- Pregnancy: Category C – use only if benefits outweigh risks.
- Children under 2 yr: contraindicated.
- Elderly: high sensitivity; prolonged effect; avoid combination with other anticholinergics.
Dosing
| Regimen | Dosage | Route | Timing | Special Note |
| Pre‑travel | 1 mg/patch (≈ 0.7 mg/24 h) | Transdermal | Apply 3 days before travel; remove after ≤ 48 h. | Provides 48‑hour coverage; avoid if skin irritation. |
| In‑hospital (PONV prophylaxis) | 0.1 mg oral or 0.1 mg IM | Oral/IM | 30 min before anesthesia; repeat every 6–8 h if needed. | Max 0.3 mg/24 h. |
| Motion sickness | 0.1–0.2 mg oral | Oral | 30 min pre‑activity; limited to 0.6 mg total/24 h. | Higher in adults; use patch for children. |
| Adjuvant | 0.25 mg subcutaneous | SC | 30 min before surgery | Not FDA‑approved in U.S.; used in some centers. |
> Patch Application: Clean, dry skin on the upper back or chest. Do not remove during the 24‑h wearing period; a patch left on longer than 48 h may cause toxicity.
Adverse Effects
| Category | Typical Adverse Events | Serious Events | Management |
| Common | Dry mouth, blurred vision, tachycardia, constipation, urinary retention, dizziness | None | Hydration, antimuscarinic‑sparing agents |
| Serious | Anticholinergic toxicity – CNS agitation, delirium, hallucinations, severe constipation leading to ileus, cardiac arrhythmias | Severe anticholinergic syndrome (especially in elderly) | Discontinue drug, IV fluids, atropine (if bradyarrhythmia), monitor mental status; consider activated charcoal if ingested < 4 h |
Monitoring
- Vital signs: heart rate, blood pressure (especially in patients with cardiovascular disease).
- Ocular pressure: screen for acute angle‑closure glaucoma if present.
- Cognition: baseline and during therapy in elderly or those with dementia.
- Renal function: serum creatinine, eGFR if prolonged use or high dose.
- Urinary retention: monitor voiding after high doses or in patients with prostatic hypertrophy.
Clinical Pearls
- Patch over oral for motion sickness: Eliminates peaks/troughs, lower incidence of nausea from the drug itself.
- Three‑day skin‑patching: Place patch 3 days before travel for optimal plasma level; remove after 48 h to prevent accumulation.
- Avoid in the elderly: They metabolize slower and have decreased sensory thresholds → increased anticholinergic toxicity. Consider switching to non‑cholinergic agents (ondansetron, dexamethasone).
- Combine wisely: When used with other antiemetics (e.g., olanzapine, promethazine), monitor for additive sedation and anticholinergic burden.
- Patch skin reaction: 5–10 % develop mild erythema or itching. If severe, switch to oral or consider other anti‑motion agents (dimenhydrinate, meclizine).
- Cardiac vigilance: In patients with a history of arrhythmia, treat with lowest effective dose; consider ECG baseline.
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• Scopolamine remains a cornerstone for motion‑related nausea and PONV prophylaxis, but its potent antimuscarinic profile demands judicious use, especially in vulnerable populations.