What is the recommended dosing of dextromethorphan for cough suppression in adults and children aged 4 years and older?

Dextromethorphan Dosing for Cough Suppression

For adults and children ≥12 years, dextromethorphan should be dosed at 30-60 mg per dose (maximum 120 mg/day), as standard over-the-counter dosing is often subtherapeutic and maximum cough suppression occurs at 60 mg. 1, 2

Adult Dosing (≥12 years)

• The optimal dose is 10-15 mg three to four times daily (every 6-8 hours), with a maximum daily dose of 120 mg. 2
• For maximum cough reflex suppression, a single 60 mg dose can be used, as this is where peak suppression occurs and can be prolonged. 1, 2
• A bedtime dose of 15-30 mg may help suppress cough and promote undisturbed sleep. 2
• The FDA-approved dosing for adults is 10 mL (containing dextromethorphan) every 12 hours, not to exceed 20 mL in 24 hours, though this may be subtherapeutic compared to guideline recommendations. 3

Pediatric Dosing

Children 6 to <12 years:

• FDA-approved dosing: 5 mL every 12 hours, not to exceed 10 mL in 24 hours. 3
• Evidence suggests a dose of approximately 0.5 mg/kg may provide better symptomatic relief while balancing adverse events, though this requires further validation. 4
• Multiple-dose studies show dextromethorphan reduces daytime cough frequency by approximately 25.5% and total 24-hour cough by 21% in this age group. 5

Children 4 to <6 years:

• FDA-approved dosing: 2.5 mL every 12 hours, not to exceed 5 mL in 24 hours. 3

Children <4 years:

• Do not use dextromethorphan in children under 4 years of age. 3

Critical Dosing Considerations

• Standard over-the-counter preparations often contain subtherapeutic doses; maximum cough suppression requires 60 mg, which is higher than typical OTC recommendations. 1, 2
• Exercise extreme caution with combination preparations containing acetaminophen or other ingredients, as higher dextromethorphan doses could lead to toxic levels of these additional components. 1, 2
• A clear dose-response relationship exists, with doses below 30 mg often providing inadequate relief. 1

Clinical Context and Alternatives

• Dextromethorphan is the preferred first-line antitussive due to its superior safety profile compared to codeine-based products, which offer no greater efficacy but significantly more adverse effects (drowsiness, nausea, constipation, physical dependence). 1, 2
• For acute viral cough, simple home remedies like honey and lemon should be considered first, as they may be as effective as pharmacological treatments. 1, 2
• For nocturnal cough, first-generation sedating antihistamines (excluding promethazine) may be more appropriate due to their sedative properties. 1, 2

Important Limitations

• Dextromethorphan has limited efficacy (<20% cough suppression) for acute upper respiratory infection cough, but demonstrates 40-60% reduction in cough frequency for chronic bronchitis/COPD-related cough. 1
• Single 30 mg doses show minimal clinical benefit in acute URI-associated cough, supporting the need for higher dosing. 6
• Dextromethorphan should only be used for short-term symptomatic relief and discontinued if cough persists beyond 3 weeks, as prolonged cough requires diagnostic workup. 2

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. 2
• Failing to check combination products for acetaminophen content when prescribing higher dextromethorphan doses. 2
• Using dextromethorphan for productive cough where secretion clearance is beneficial. 2