What is the recommended dose of promethazine (Phenergan) for treating a cough in adults and children?

Promethazine Dosing for Cough

Promethazine is not recommended for cough treatment in either adults or children, as it has no proven efficacy for this indication and carries significant safety risks, particularly in pediatric populations.

Why Promethazine Should Not Be Used for Cough

Lack of Efficacy

• Promethazine showed no superiority over placebo for nocturnal cough in children with upper respiratory infections in a randomized controlled trial, with all groups improving equally over 3 days regardless of treatment 1
• The British Thoracic Society guidelines do not recommend promethazine for cough management, instead favoring dextromethorphan, menthol, or first-generation sedating antihistamines for nocturnal cough 2, 3

Safety Concerns

• Promethazine is absolutely contraindicated in children under 2 years of age due to risk of fatal respiratory depression 4
• Significant adverse effects include sedation, agitation, hallucinations, seizures, dystonic reactions, and possible sudden infant death syndrome 5
• When administered intravenously, promethazine can cause hypotension (especially with rapid infusion), neuroleptic malignant syndrome, extrapyramidal effects, and severe local tissue damage including gangrene with extravasation 6

Recommended Alternatives for Cough

First-Line Treatments

• Simple home remedies such as honey and lemon are the simplest, cheapest, and often effective first-line treatment for acute cough 3
• Voluntary cough suppression through central modulation may be sufficient 3

Pharmacological Options (When Needed)

• Dextromethorphan is the preferred antitussive with proven efficacy in meta-analysis for acute cough 2, 3

  • Dose: 60 mg provides maximum cough suppression with dose-response relationship 2, 3
  • Non-sedating opiate with better safety profile than codeine or pholcodine 2
  • Caution: Some preparations contain additional ingredients like paracetamol 3

• Menthol by inhalation suppresses cough reflex acutely but effect is short-lived 2, 3

  • Can be prescribed as menthol crystals or proprietary capsules 3

• First-generation sedating antihistamines (not promethazine specifically) may be suitable for nocturnal cough due to sedative properties 2, 3

When to Consider Underlying Causes

• For persistent cough, evaluate for gastroesophageal reflux disease (GERD), which may require proton pump inhibitors (omeprazole 20-40 mg twice daily) for at least 8 weeks to 3 months 2, 3
• For cough with upper airway symptoms, trial topical corticosteroids for 1 month 2, 3
• Consider cough variant asthma or eosinophilic bronchitis, which respond to inhaled corticosteroids 2

Critical Pitfall to Avoid

Do not use promethazine for cough simply because it is labeled as an antihistamine or antiemetic - its approved indications are for allergies, motion sickness, nausea/vomiting, and sedation, not cough 4. The FDA-approved dosing for allergies (12.5-25 mg) or nausea (25 mg) should never be extrapolated to cough treatment, as this indication lacks evidence and poses unnecessary risk 4, 1.