What is the recommended dosage and frequency of dextromethorphan (cough suppressant) for an adult or adolescent patient with a dry cough and no significant medical history?

Dextromethorphan Dosing and Frequency for Dry Cough

For adults and adolescents with dry cough, dextromethorphan should be dosed at 30-60 mg every 12 hours (maximum 120 mg daily), as standard over-the-counter doses are often subtherapeutic and maximum cough suppression occurs at 60 mg. 1, 2

Recommended Dosing Regimen

Standard Dosing

• Adults and adolescents ≥12 years: 10-15 mg three to four times daily, with maximum daily dose of 120 mg 1
• For optimal cough suppression, a single dose of 60 mg provides maximum cough reflex suppression and can be prolonged 1, 2
• The FDA-approved extended-release formulation recommends 10 mL (containing dextromethorphan) every 12 hours, not exceeding 20 mL in 24 hours for adults 3

Key Dosing Considerations

• Standard over-the-counter doses are frequently subtherapeutic and may not provide adequate relief 1, 2
• A clear dose-response relationship exists, with maximum efficacy achieved at 60 mg 1, 2, 4
• When prescribing higher doses (60 mg), verify that combination products do not contain excessive amounts of other ingredients like acetaminophen 1, 2

Treatment Algorithm

First-Line Approach

• Begin with simple home remedies (honey and lemon) before pharmacological treatment, as these may be equally effective for benign viral cough 1, 2, 4
• Consider voluntary cough suppression techniques through central modulation 1, 2

When Pharmacological Treatment Is Needed

• Start dextromethorphan at 30-60 mg for short-term symptomatic relief 1, 2
• Dextromethorphan is the preferred antitussive due to superior safety profile compared to codeine-based alternatives 1, 2, 4
• For nocturnal cough disrupting sleep, consider first-generation sedating antihistamines as an alternative 1, 2, 4

Duration of Treatment

• Use dextromethorphan for short-term symptomatic relief only 1
• Discontinue and perform full diagnostic workup if cough persists beyond 3 weeks 1, 2

Important Safety Considerations

When NOT to Use Dextromethorphan

• Do not use in patients requiring assessment for pneumonia (tachycardia, tachypnea, fever, abnormal chest examination) 2, 4
• Avoid in productive cough where secretion clearance is beneficial 1, 2
• Not recommended for routine use in acute bronchitis due to inconsistent efficacy 1

Common Prescribing Pitfalls

• Using subtherapeutic doses (<60 mg) that fail to provide adequate cough suppression 1, 2, 4
• Prescribing codeine-based products, which offer no efficacy advantage over dextromethorphan but have significantly worse adverse effects (drowsiness, nausea, constipation, physical dependence) 1, 2, 4, 5
• Suppressing productive cough in conditions like pneumonia or bronchiectasis where clearance is essential 2, 4
• Continuing antitussive therapy beyond 3 weeks without investigating underlying causes 1, 2

Alternative and Adjunctive Options

For Postinfectious Cough

• Try inhaled ipratropium before central antitussives like dextromethorphan 1, 2
• For severe paroxysms after ipratropium failure, consider prednisone 30-40 mg daily for a short course 1, 2
• Dextromethorphan should only be considered when other measures fail 1, 2

For Quick Temporary Relief

• Menthol inhalation provides acute but short-lived cough suppression 1, 2
• Can be prescribed as menthol crystals or proprietary capsules 2

Special Populations

Chronic Kidney Disease

• No dose adjustment required for patients with CKD, as dextromethorphan is primarily metabolized hepatically by CYP2D6, not renally excreted 1

Pediatric Considerations

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