What are the guidelines for using prescription dextromethorphan (cough suppressant) in adults and children?

Prescription Dextromethorphan Guidelines

Recommended Indications and Dosing

Prescription dextromethorphan is recommended specifically for chronic bronchitis at 10-15 mg three to four times daily (maximum 120 mg/day), but is NOT recommended for acute upper respiratory infections or common cold-related cough. 1, 2

Evidence-Based Indications

• Chronic bronchitis: Dextromethorphan is recommended for short-term symptomatic relief with fair evidence and intermediate benefit (Grade B recommendation) 1
• NOT recommended for URI/common cold: Despite widespread use, central cough suppressants including dextromethorphan have limited efficacy for acute upper respiratory infection cough with good evidence showing no benefit (Grade D recommendation) 1, 2
• Postinfectious cough: Consider dextromethorphan only as a last resort after inhaled ipratropium and other measures have failed 2, 3

Dosing Regimen

Adults:

• Standard dosing: 10-15 mg three to four times daily, maximum 120 mg/day 2, 4
• Maximum single-dose suppression: 60 mg provides optimal cough reflex suppression with dose-response relationship 2, 3
• Critical caveat: Standard over-the-counter dosing (30 mg) is often subtherapeutic and may not provide adequate relief 2, 3

Pediatric dosing (per FDA label):

• Ages 12+ years: 10 mL every 12 hours (maximum 20 mL/24 hours) 5
• Ages 6-11 years: 5 mL every 12 hours (maximum 10 mL/24 hours) 5
• Ages 4-5 years: 2.5 mL every 12 hours (maximum 5 mL/24 hours) 5
• Under 4 years: Do not use 5

Clinical Algorithm for Use

Step 1: Determine Cough Type and Duration

• Dry, non-productive cough: Potential candidate for dextromethorphan 4
• Productive cough with sputum: Do NOT suppress - cough serves physiological purpose to clear secretions 4
• Duration < 3 weeks: Consider simple remedies first 2, 3
• Duration > 3 weeks: Requires full diagnostic workup, not continued antitussive therapy 2, 4

Step 2: First-Line Approach (Before Dextromethorphan)

• Start with honey and lemon - as effective as pharmacological treatments, cheapest and simplest option 2, 3, 4
• Voluntary cough suppression through central modulation may be sufficient 2, 3

Step 3: When to Use Dextromethorphan

• Chronic bronchitis with dry cough: Appropriate indication 1, 2
• Postinfectious cough: Only after ipratropium fails 2, 3
• Nocturnal cough disrupting sleep: Consider first-generation sedating antihistamines instead, as they provide dual benefit of cough suppression and sedation 2, 3, 4

Step 4: When NOT to Use Dextromethorphan

• Acute viral URI/common cold: No proven benefit 1, 2
• Productive cough: Suppression counterproductive 4
• Suspected pneumonia: Must rule out first (tachycardia, tachypnea, fever, abnormal chest exam) 2
• Concurrent MAOI use: Significant drug interaction risk 6

Comparative Efficacy and Safety

Dextromethorphan is superior to codeine in safety profile with equivalent or better efficacy:

• Codeine and pholcodine have no greater efficacy than dextromethorphan 1, 2
• Codeine has significantly worse adverse effects: drowsiness, nausea, constipation, physical dependence 2, 3, 4
• Dextromethorphan demonstrated greater reduction in cough intensity than codeine (p < 0.0008) and was preferred by patients (p < 0.001) 7
• Dextromethorphan has reassuring safety profile, particularly regarding overdose in adults and children 6

Critical Pitfalls to Avoid

• Using subtherapeutic doses: Standard OTC 30 mg doses may be insufficient; consider 60 mg for maximum suppression 2, 3, 4
• Prescribing for acute URI: No evidence of benefit despite widespread practice 1, 2
• Suppressing productive cough: Prevents necessary secretion clearance 4
• Combination products: Exercise caution with preparations containing acetaminophen or other ingredients when using higher doses 2, 3
• Prolonged use without workup: Cough persisting beyond 3 weeks requires diagnostic evaluation, not continued suppression 2, 4
• Prescribing codeine instead: No efficacy advantage with worse side effect profile 1, 2, 4

Special Considerations

Drug Interactions

• Contraindicated with MAOIs: Serious interaction risk requiring avoidance 6

Abuse Potential

• Abuse at high doses (>1500 mg/day) can induce PCP-like psychosis with delusions, hallucinations, and paranoia 8
• Not detected on standard urine drug screens, making abuse under-recognized 8
• Some states restrict sales to individuals over 18 years 8

Adverse Effects

• Generally infrequent and not severe 6
• Dose-related: neurological, cardiovascular, and gastrointestinal disturbances 6
• Adverse events occur most often with higher doses 9

Duration of Treatment

• Use for short-term symptomatic relief only 1, 2
• Discontinue if no improvement after short course 2
• If cough persists beyond 8 weeks in postinfectious setting, consider diagnoses other than postinfectious cough 2