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Antihistamine / antiemetic (theoclate salt of diphenhydramine) Pregnancy: Avoid 1st trimester — limited data. Cinnarizine or doxylamine + pyridoxine preferred.

Dimenhydrinate

Brand names: Dramamine

Adult dose

Dose: Motion sickness prevention: 50–100 mg PO 30–60 min before travel; repeat every 4–6 hours as needed. Vertigo / vestibular nausea: 50 mg every 4–6 hours.
Route: Oral / IM (rare in UK)
Frequency: Every 4–6 hours
Max: 400 mg/day
Sedating — counsel about driving. Limited UK availability (Dramamine widely OTC in US/Europe; UK travellers more often use cinnarizine 15–30 mg or hyoscine). Onset 30 min, duration 4–6 hours.

Paediatric dose

Dose: 1.25 mg/kg
Route: Oral
Frequency: Every 6–8 hours
Max: 75 mg/day (2–6 yrs); 150 mg/day (6–12 yrs)
2–6 yrs: 12.5–25 mg every 6–8 hours. 6–12 yrs: 25–50 mg every 6–8 hours. ≥12 yrs adult dose. Avoid <2 yrs.

Dose adjustments

Renal

Caution; reduce dose in severe impairment.

Hepatic

Caution.

Paediatric weight-based calculator

2–6 yrs: 12.5–25 mg every 6–8 hours. 6–12 yrs: 25–50 mg every 6–8 hours. ≥12 yrs adult dose. Avoid <2 yrs.

Clinical pearls

  • Diphenhydramine + 8-chlorotheophylline (theoclate) — combines sedating antihistamine with mild stimulant; widely OTC outside UK as Dramamine.
  • In UK, motion sickness OTC standards: cinnarizine (Stugeron) 15 mg 2 hours before travel, then 15 mg every 8 hours; or hyoscine hydrobromide (Joy-Rides, Kwells).
  • First-generation antihistamines may MASK aminoglycoside ototoxicity symptoms — caution in patients on streptomycin/gentamicin.
  • Avoid in elderly — Beers Criteria flag for falls and confusion.
  • Pregnancy motion sickness: doxylamine + pyridoxine (Xonvea) is a UK-licensed alternative for nausea/vomiting; cinnarizine has more pregnancy data than dimenhydrinate.
  • Vertigo: prochlorperazine, betahistine, or cinnarizine more commonly used in UK.

Contraindications

  • Children <2 years (severe sedation, anticholinergic toxicity)
  • Acute narrow-angle glaucoma
  • Bladder neck obstruction, severe BPH
  • Pyloroduodenal obstruction
  • MAOI within 14 days
  • Hypersensitivity

Side effects

  • Sedation, drowsiness (very common — first-generation H1)
  • Dry mouth, blurred vision
  • Urinary retention, constipation (anticholinergic)
  • Tachycardia, palpitations
  • Photosensitivity
  • Paradoxical excitation (children, elderly)
  • Confusion in elderly
  • Dependence (low — but theoclate component has stimulant effect)

Interactions

  • Other CNS depressants (alcohol, benzodiazepines, opioids): additive sedation
  • Anticholinergics: additive antimuscarinic toxicity
  • MAOIs: hypertensive crisis — avoid
  • Aminoglycosides / ototoxic drugs: may MASK ototoxicity symptoms

Monitoring

  • Symptom response
  • Sedation / cognitive impact in elderly

Reference: BNFc; BNF 90; SmPC Dramamine; NICE CKS Vertigo; NHS Travel Health. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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