Phenargan dosage and when to take for motion sickness
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Phenergan promethazine dosage motion sickness adults children
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Phenergan (Promethazine) for Motion Sickness
Phenergan is the brand name for promethazine hydrochloride, a first-generation antihistamine and phenothiazine derivative. It works by blocking H1 receptors and has anticholinergic properties, both of which contribute to suppression of the vestibular input that triggers motion sickness nausea.
Dosing for Motion Sickness
Adults (and teenagers)
| Timing | Dose |
|---|---|
| First dose - 30 to 60 min before travel | 25 mg |
| Repeat if needed | 25 mg, 8-12 hours later |
| Ongoing days of travel | 25 mg on arising + 25 mg before the evening meal |
Children (2 years and older)
- 12.5 to 25 mg, given 30-60 minutes before travel
- May repeat 8-12 hours later if needed
- Dose is adjusted by weight (roughly 0.5 mg/kg)
Important warning: Phenergan is contraindicated in children under 2 years of age due to risk of fatal respiratory depression. In Australia, it is not recommended under 6 years, and used with caution in children aged 6-12 only on pharmacist or medical advice.
Timing - Key Points
- Take it before you feel sick - it is a preventive, not a rescue treatment. It is "usually not effective if given after the onset of symptoms" (Lippincott Pharmacology).
- Ideally take it the night before a long journey or at least 30-60 minutes before departure.
- On multi-day trips, take 25 mg each morning on arising and again before the evening meal.
Available Formulations
- Tablets (10 mg, 25 mg)
- Syrup/Elixir
- Rectal suppositories (when oral route not tolerated)
- Injection (IM/IV - hospital use)
Important Side Effects & Precautions
| Side Effect | Notes |
|---|---|
| Sedation | Marked - do not drive or operate machinery |
| Anticholinergic effects | Dry mouth, blurred vision, urinary retention |
| Extrapyramidal reactions | Especially at higher doses |
| Respiratory depression | Risk is highest in young children |
| Alpha-adrenergic blockade | Can cause hypotension |
Avoid if you have: epilepsy, narrow-angle glaucoma, prostatic hypertrophy, severe liver disease, or are taking other CNS depressants (including alcohol, opioids, benzodiazepines - effects are additive).
Pregnancy: Use only if clearly needed; consult a doctor.
How It Compares to Other Motion Sickness Options
Promethazine is among the most effective antihistamines for motion sickness - more effective than meclizine or cyclizine - but also causes more sedation (Goodman & Gilman's, Katzung's). Scopolamine (patch) is similarly effective with a slightly different side-effect profile. For those wanting less drowsiness, meclizine (Bonine) is a reasonable alternative.
Sources: Katzung's Basic and Clinical Pharmacology 16th Ed; Goodman & Gilman's Pharmacological Basis of Therapeutics; Drugs.com Phenergan Dosage Guide; Mayo Clinic - Promethazine; StatPearls - Promethazine
Disclaimer: This is for informational purposes. Always follow your doctor's or pharmacist's advice for your specific situation, especially for children or if you have any underlying health conditions.
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