What are the uses and dosage instructions for Dextromethorphan?

Dextromethorphan: Uses and Dosing

Dextromethorphan is the preferred first-line antitussive for dry cough due to its superior safety profile compared to codeine-based alternatives, with optimal cough suppression achieved at 60 mg—substantially higher than standard over-the-counter dosing. 1, 2

Primary Indication

Dextromethorphan is a non-sedating opiate that centrally suppresses the cough reflex and is indicated for symptomatic relief of dry, non-productive cough associated with:

• Acute viral upper respiratory tract infections 1, 3
• Common cold 3
• Acute bronchitis (for short-term symptomatic relief only) 2
• Postinfectious cough (when other measures fail) 2

Dosing Recommendations

Standard FDA-Approved Dosing 4

• Adults and children ≥12 years: 10 mL (30 mg) every 12 hours, maximum 20 mL (60 mg) in 24 hours
• Children 6 to <12 years: 5 mL (15 mg) every 12 hours, maximum 10 mL (30 mg) in 24 hours
• Children 4 to <6 years: 2.5 mL (7.5 mg) every 12 hours, maximum 5 mL (15 mg) in 24 hours
• Children <4 years: Do not use

Evidence-Based Optimal Dosing

Critical caveat: Standard over-the-counter dosing is often subtherapeutic. 1, 2 The evidence demonstrates:

• Maximum cough suppression occurs at 60 mg single dose 1, 2
• A clear dose-response relationship exists, with 30 mg providing modest benefit (19-36% reduction in cough) but 60 mg achieving maximal effect 2, 5
• For lung cancer-associated cough, guidelines recommend 10-15 mg three to four times daily (maximum 120 mg/24 hours) 2

Alternative Dosing Strategy

For adults requiring maximum cough suppression, consider 30-60 mg as a single dose, recognizing this exceeds typical OTC recommendations but aligns with physiologic data on cough reflex suppression 1, 2

Clinical Application Algorithm

First-Line Approach

1. Start with non-pharmacological measures: Honey and lemon mixtures are as effective as pharmacological treatments for benign viral cough 1, 2, 3
2. Consider voluntary cough suppression techniques to reduce cough frequency through central modulation 1, 2

When Pharmacological Treatment Is Needed

1. Use dextromethorphan 30-60 mg for daytime cough requiring suppression 1, 2
2. For nocturnal cough disrupting sleep: Consider first-generation sedating antihistamines instead, as drowsiness becomes therapeutic 1, 2, 3
3. For quick but temporary relief: Menthol inhalation provides acute, short-lived cough suppression 1, 3

For Postinfectious Cough (Specific Algorithm)

1. First: Try inhaled ipratropium 2
2. Second: If ipratropium fails, use dextromethorphan as central antitussive 2
3. Third: For severe paroxysms unresponsive to above, consider prednisone 30-40 mg daily for short course 2

Important Contraindications and Precautions

Do NOT Use Dextromethorphan When:

• Pneumonia must be ruled out first in patients with tachycardia, tachypnea, fever, or abnormal chest examination 1
• Productive cough where secretion clearance is beneficial 2
• Cough with increasing breathlessness (assess for asthma or anaphylaxis) 1
• Cough with fever, malaise, purulent sputum (may indicate serious lung infection) 1
• Significant hemoptysis or possible foreign body inhalation (requires specialist referral) 1

Critical Safety Warning

Exercise caution with combination preparations containing acetaminophen or other ingredients—higher doses of dextromethorphan (60 mg) in multi-ingredient products risk toxic levels of co-formulated drugs 1, 2

Duration of Treatment

• Use for short-term symptomatic relief only 2
• Cough persisting >3 weeks requires full diagnostic workup rather than continued antitussive therapy 2
• Discontinue if no improvement after short trial 2

Comparative Efficacy

Superior to Codeine

Dextromethorphan has equivalent or superior efficacy to codeine with significantly fewer adverse effects (no drowsiness, nausea, constipation, or physical dependence risk) 1, 2, 3, 6. Codeine and pholcodine are not recommended due to their poor benefit-to-risk ratio 1, 2, 3.

Evidence Limitations

The evidence for dextromethorphan efficacy is mixed—one meta-analysis supports its use 1, 3, but individual studies show inconsistent results, with some demonstrating no significant difference from placebo at standard 30 mg dosing 2, 7. This inconsistency likely reflects subtherapeutic dosing in many trials, as the dose-response data clearly shows 60 mg is required for maximal effect 1, 2.

Common Pitfalls to Avoid

1. Using subtherapeutic doses (standard OTC 15-30 mg may be insufficient) 1, 2
2. Prescribing codeine-based products (no efficacy advantage, worse side effects) 1, 2, 3
3. Continuing treatment beyond 3 weeks without diagnostic evaluation 2
4. Using for productive cough where expectoration is beneficial 2
5. Overlooking combination product ingredients when prescribing higher doses 1, 2