What is the recommended promethazine and codeine dosing regimen for an adult with a non‑productive cough?

Promethazine with Codeine Dosing for Cough

Promethazine with codeine is not recommended for cough suppression due to lack of efficacy advantage over safer alternatives and a significantly worse adverse effect profile. 1

Why This Combination Should Be Avoided

Codeine Component

• Codeine has no greater efficacy than dextromethorphan for cough suppression 2, 1
• Codeine carries a much greater adverse side effect profile including drowsiness, nausea, constipation, and physical dependence 2, 3
• The British Thoracic Society explicitly states that codeine-based antitussives are not recommended 2

Promethazine Component

• Promethazine has no established efficacy for cough suppression and is primarily indicated for nausea, allergic conditions, and sedation 1
• Promethazine is associated with serious adverse effects including hypotension, respiratory depression, neuroleptic malignant syndrome, and extrapyramidal reactions such as restlessness and oculogyric crises 1
• The British Thoracic Society recommends against using promethazine for cough management 1

Recommended Alternative Approach

First-Line Treatment

• Start with simple home remedies like honey and lemon, which may be as effective as pharmacological treatments for benign viral cough 1, 3, 4
• Consider voluntary cough suppression techniques through central modulation 1, 3

Preferred Pharmacological Agent

• Dextromethorphan alone is the recommended first-line antitussive due to superior safety profile 2, 1, 4
• Dosing: 30-60 mg for optimal cough suppression (maximum daily dose 120 mg) 1, 4
• Standard over-the-counter dosing of 15-30 mg is often subtherapeutic 1, 4
• Maximum cough reflex suppression occurs at 60 mg and can be prolonged 2, 1
• Can be dosed as 10-15 mg three to four times daily (every 6-8 hours) 1
• A bedtime dose of 15-30 mg may help suppress nocturnal cough 1

For Nocturnal Cough Specifically

• First-generation sedative antihistamines (NOT promethazine) may be suitable for nighttime cough due to sedative properties 2, 3, 4
• These suppress cough but cause drowsiness, making them particularly appropriate when cough disrupts sleep 2, 4

Additional Options

• Menthol inhalation provides acute but short-lived cough suppression 2, 3, 4
• Can be prescribed as menthol crystals or proprietary capsules 3

Critical Safety Considerations

• Exercise caution with higher doses of dextromethorphan as some combination preparations contain other ingredients like acetaminophen 2, 1
• Dextromethorphan should be used for short-term symptomatic relief only (typically less than 7 days) 4
• Do not use antitussives for productive cough where clearance of secretions is beneficial 1, 4

Common Pitfalls to Avoid

• Prescribing codeine-containing products which have no efficacy advantage but increased side effects 2, 1, 3
• Using subtherapeutic doses of dextromethorphan (less than 30-60 mg) that may not provide adequate relief 1, 4
• Prescribing promethazine for cough when it has no established efficacy for this indication 1
• Continuing antitussive therapy beyond short-term use without reassessing the underlying cause 1

When to Reconsider the Approach

• If cough persists beyond 3 weeks, a full diagnostic workup is required rather than continued antitussive therapy 1
• For postinfectious cough, try inhaled ipratropium before central antitussives 1, 4
• For severe paroxysms of postinfectious cough, consider short-course prednisone 30-40 mg daily 1, 4