Dimenhydrinate: Antihistamine for Nausea and Motion Sickness
Dimenhydrinate (Dramamine, Vomex) is the theophyllinate salt of diphenhydramine. As a first-generation H1 antihistamine with anticholinergic properties, it effectively prevents and treats nausea, vomiting, and dizziness associated with motion sickness and vestibular disorders.
Available over-the-counter in most countries, dimenhydrinate has been used since the 1950s. It causes significant sedation, which may be desired in some situations (night travel) but limits daytime use.
Mechanism of Action
Dimenhydrinate blocks H1 histamine receptors and muscarinic acetylcholine receptors in the vestibular apparatus, vomiting centre, and chemoreceptor trigger zone. This combination reduces labyrinthine excitability and suppresses nausea and vomiting signals.
Indications & Use
Prevention and treatment of nausea, vomiting, and dizziness caused by motion sickness, inner ear disorders (labyrinthitis, Meniere's disease), post-operative nausea, and radiation sickness. Also used as a sedative adjunct in mild anxiety states.
Dosage
Adults: 50–100 mg every 4–6 hours (max 400 mg/day). Children (6–12 years): 25–50 mg every 6–8 hours. Motion sickness prevention: take 30–60 minutes before travel. Suppositories: 150 mg (adults), 40–70 mg (children).
Side Effects
Very common: sedation (may be severe), dry mouth. Common: dizziness, urinary retention, constipation, blurred vision, paradoxical CNS stimulation in children. Rare: haemolytic anaemia, thrombocytopenia.
Drug Interactions
CNS depressants, opioids, alcohol: markedly potentiated sedation. Other anticholinergics: increased anticholinergic toxicity. MAO inhibitors: prolonged and intensified anticholinergic effects. Ototoxic drugs: may mask ototoxicity symptoms.
Contraindications
Narrow-angle glaucoma, urinary obstruction, epilepsy (seizure threshold lowered), premature neonates. Caution: elderly, severe liver disease, asthma, porphyria.
Frequently Asked Questions
Is dimenhydrinate safe for children?
Dimenhydrinate is approved for children over 2 years old, with weight-adjusted dosing. Paradoxical excitation can occur. Never give to premature infants. Always follow age and weight guidelines.
Can dimenhydrinate be used during pregnancy?
Limited evidence; generally considered low risk in the first and second trimesters. Avoid prolonged use near term. Consult your healthcare provider.
Why does dimenhydrinate cause so much drowsiness?
Dimenhydrinate readily crosses the blood-brain barrier and blocks H1 receptors in the brain, causing significant sedation. This can be used therapeutically for travel or as a sleep aid but impairs driving.
References
- EMA assessment of dimenhydrinate
- AAP guidelines on antiemetics
- NICE guidance on nausea and vomiting
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.