What are the appropriate dextromethorphan doses for cough suppression in adults and in children aged 4–12 years, and what are the contraindications (e.g., age < 4, monoamine‑oxidase inhibitor use, severe hepatic impairment)?

Dextromethorphan Dosing for Cough Suppression

Adult Dosing

For adults requiring pharmacological cough suppression, dextromethorphan should be dosed at 30–60 mg every 6–8 hours (maximum 120 mg/day), as standard over-the-counter doses of 10–15 mg are subtherapeutic and inadequate for meaningful cough relief. 1, 2

Optimal Dosing Strategy

• Maximum cough reflex suppression occurs at 60 mg per dose, with prolonged effect at this level 1, 2
• Standard dosing: 10–15 mg three to four times daily is the minimum effective regimen 1, 2
• For severe cough or nighttime use: 30–60 mg at bedtime can suppress cough and promote undisturbed sleep 1, 2
• Doses below 30 mg are inadequate for meaningful cough suppression in most patients 2

Critical Safety Consideration

• Exercise caution with combination preparations containing acetaminophen or other ingredients, as higher doses of dextromethorphan (60 mg) could lead to toxic levels of these additional components 1, 2

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Pediatric Dosing (Ages 4–12 Years)

According to FDA labeling, children aged 6 to under 12 years should receive 5 mL (containing dextromethorphan) every 12 hours, not exceeding 10 mL in 24 hours; children aged 4 to under 6 years should receive 2.5 mL every 12 hours, not exceeding 5 mL in 24 hours. 3

Age-Specific Dosing from FDA Label

• Ages 6 to <12 years: 5 mL every 12 hours (maximum 10 mL/24 hours) 3
• Ages 4 to <6 years: 2.5 mL every 12 hours (maximum 5 mL/24 hours) 3
• Under 4 years: Do not use 3

Important Pediatric Considerations

• Research suggests a dose of approximately 0.5 mg/kg may balance symptomatic relief with adverse event avoidance in children, though this is not yet standard practice 4
• The efficacy of dextromethorphan for acute cough in children and adolescents has not been clearly demonstrated 5

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Absolute Contraindications

Dextromethorphan is contraindicated in children under 4 years of age per FDA labeling. 3

Additional Contraindications (Based on Clinical Guidelines)

• Concurrent monoamine oxidase inhibitor (MAOI) use: Risk of serotonin syndrome and severe drug interactions 1
• Severe hepatic impairment: Dextromethorphan is primarily metabolized by CYP2D6 hepatically 2
• Productive cough where secretion clearance is beneficial (e.g., pneumonia, bronchiectasis): Suppressing protective cough mechanisms is harmful 1, 2

Clinical Scenarios Requiring Alternative Management

• Patients requiring assessment for pneumonia (tachycardia, tachypnea, fever, abnormal chest examination): Pneumonia must be ruled out first before using antitussives 1
• Cough persisting beyond 3 weeks: Requires full diagnostic workup rather than continued antitussive therapy 2

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Comparative Safety Profile

Dextromethorphan has a superior safety profile compared to codeine-based antitussives, with no risk of physical dependence, constipation, or respiratory depression. 1, 2, 6

Why Dextromethorphan Over Codeine

• Codeine provides no greater cough-suppression efficacy than dextromethorphan 1, 2, 6
• Codeine carries significantly higher adverse effects: drowsiness, nausea, constipation, physical dependence 1, 2, 6
• The British Thoracic Society explicitly recommends against codeine-containing antitussives 2

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Special Populations

Chronic Kidney Disease

• No dose adjustment required for patients with chronic kidney disease, as dextromethorphan is hepatically metabolized via CYP2D6, not renally excreted 1

Geriatric Patients

• Exercise caution as geriatric patients may have increased clearance time and be more susceptible to adverse effects, particularly at higher doses 7
• Slow metabolizers at CYP2D6 may be at risk for psychosis with excessive dosing 7

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Common Prescribing Pitfalls to Avoid

• Using subtherapeutic doses (<30 mg) that fail to provide adequate cough relief 1, 2
• Prescribing codeine-containing products which lack efficacy advantage and increase side-effect burden 1, 2, 6
• Failing to check combination products for acetaminophen content when prescribing higher doses 1, 2
• Suppressing productive cough in conditions requiring secretion clearance 1, 2

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Alternative First-Line Approach

Simple home remedies like honey and lemon should be considered first for benign viral cough, as they may be as effective as pharmacological treatments without adverse effects. 1, 2, 6

• For nocturnal cough disrupting sleep: First-generation sedating antihistamines (e.g., diphenhydramine) may be used 1, 2, 6
• For acute, short-lived relief: Menthol inhalation provides temporary cough suppression 1, 2