What is the recommended dextromethorphan dose for a healthy adult and for children (ages 2‑5 and 6‑12), and what are its contraindications?

Dextromethorphan Dosing and Contraindications

For healthy adults, dextromethorphan should be dosed at 30-60 mg every 4-6 hours (maximum 120 mg/day), with optimal cough suppression achieved at 60 mg; for children ages 6-12 years, the dose is 15 mg (or 5 mL of extended-release formulation) every 12 hours (maximum 30 mg/24 hours), and for children ages 2-5 years, 7.5 mg (or 2.5 mL of extended-release formulation) every 12 hours (maximum 15 mg/24 hours), while dextromethorphan is contraindicated in children under 4 years of age and should not be used concurrently with monoamine oxidase inhibitors (MAOIs). 1, 2, 3, 4

Adult Dosing Recommendations

Standard Therapeutic Dosing

• The optimal dose for maximal cough suppression in adults is 60 mg, which provides superior efficacy compared to standard over-the-counter doses of 10-15 mg that are often subtherapeutic. 1, 2, 3
• The American College of Chest Physicians recommends 10-15 mg three to four times daily (every 6-8 hours) as a starting dose, with a maximum daily dose of 120 mg. 1
• For adults 12 years and older using extended-release formulations, the FDA-approved dosing is 10 mL every 12 hours, not to exceed 20 mL in 24 hours. 4
• A bedtime dose of 15-30 mg may help suppress nocturnal cough and promote undisturbed sleep. 1

Dose-Response Relationship

• Maximum cough reflex suppression occurs at 60 mg and can be prolonged at this level, representing a clear dose-response relationship. 1, 2, 3
• Standard over-the-counter dosing is frequently inadequate for meaningful symptom control. 1, 2

Pediatric Dosing Recommendations

Children Ages 6-12 Years

• 15 mg (or 5 mL of extended-release formulation) every 12 hours, not to exceed 30 mg (10 mL) in 24 hours. 4
• This corresponds to approximately 0.45-0.60 mg/kg per dose for most children in this age range. 5

Children Ages 2-5 Years (Ages 4-5 Only)

• 7.5 mg (or 2.5 mL of extended-release formulation) every 12 hours, not to exceed 15 mg (5 mL) in 24 hours. 4
• This corresponds to approximately 0.35-0.50 mg/kg per dose for most children in this age range. 5

Critical Age Restriction

• Dextromethorphan is contraindicated in children under 4 years of age per FDA labeling. 4
• The original age range of 2-5 years in older literature has been superseded by current FDA guidance restricting use to children 4 years and older. 4

Pediatric Dosing Considerations

• Research suggests that doses of 0.5 mg/kg may provide optimal balance between symptomatic relief and avoidance of adverse events in children, though this is not yet reflected in standard dosing recommendations. 5
• Age-based dosing (rather than weight-based) results in substantial variability in relative drug exposure, with some children receiving subtherapeutic doses. 5

Absolute Contraindications

Concurrent MAOI Use

• Dextromethorphan is absolutely contraindicated with concurrent or recent (within 14 days) use of monoamine oxidase inhibitors (MAOIs), as this combination can precipitate serotonin syndrome with potentially fatal consequences. 6
• This represents the most serious drug interaction and safety concern with dextromethorphan use. 6

Age Restriction

• Do not use in children under 4 years of age per current FDA guidance. 4

Relative Contraindications and Precautions

Clinical Scenarios Requiring Alternative Management

• Do not use in patients requiring assessment for pneumonia (characterized by tachycardia, tachypnea, fever, or abnormal chest examination), as pneumonia must be ruled out first. 2
• Avoid in productive cough where secretion clearance is beneficial, such as in pneumonia, bronchiectasis, or chronic bronchitis with significant sputum production. 2, 3
• Do not suppress cough in asthma or COPD if it serves a protective clearance function; treat the underlying disease instead. 2

Genetic Polymorphism Consideration

• Approximately 5% of persons of European ethnicity are CYP2D6 poor metabolizers who lack the ability to metabolize dextromethorphan normally, leading to rapid accumulation and potential toxicity. 7
• However, this polymorphism has not been correlated with clinically significant safety risk when used for short-term treatment at recommended doses. 6
• The terminal half-life is prolonged in poor metabolizers, but routine genotyping is not recommended for clinical use. 8

Critical Safety Warnings

Combination Product Hazards

• Exercise extreme caution with higher doses of dextromethorphan in combination products that contain acetaminophen, as doses approaching 60 mg of dextromethorphan may deliver toxic amounts of acetaminophen. 1, 2, 3
• Always verify the complete ingredient list before prescribing or recommending higher doses. 1

Abuse Potential

• Abuse is the most significant safety hazard identified through adverse event reporting, particularly among adolescents. 6, 7
• Megadoses (5-10 times the recommended dose) produce phencyclidine (PCP)-like effects and can cause false-positive urine screens for PCP. 7
• Pure dextromethorphan powder is easily available online, facilitating abuse. 7

Duration of Use

• Cough lasting more than 3 weeks requires full diagnostic workup, not continued antitussive therapy. 1, 3
• Dextromethorphan should be used for short-term symptomatic relief only. 1

Practical Prescribing Algorithm

Step 1: Rule Out Serious Causes

• Assess for pneumonia (fever, tachypnea, tachycardia, abnormal chest exam). 2
• Evaluate for hemoptysis, foreign body aspiration, or progressive breathlessness requiring immediate specialist referral. 2

Step 2: Consider Non-Pharmacological Approaches First

• Recommend honey and lemon mixture as first-line treatment for benign viral cough. 1, 2, 3
• Teach voluntary cough suppression techniques through central modulation. 1, 2

Step 3: Pharmacological Treatment When Needed

• For adults: Start with 30-60 mg every 6-8 hours (maximum 120 mg/day), using single-ingredient preparations. 1, 2, 3
• For children 6-12 years: 15 mg every 12 hours (maximum 30 mg/24 hours). 4
• For children 4-5 years: 7.5 mg every 12 hours (maximum 15 mg/24 hours). 4

Step 4: Adjunctive Options for Specific Scenarios

• For nocturnal cough disrupting sleep: Add first-generation sedating antihistamine at bedtime (not promethazine). 1, 2
• For acute breakthrough symptoms: Menthol inhalation provides short-lived relief. 1, 2

Common Prescribing Pitfalls to Avoid

• Using subtherapeutic doses (less than 30 mg in adults) that fail to provide adequate cough relief. 1, 2
• Prescribing codeine-containing products, which have no efficacy advantage over dextromethorphan but significantly more adverse effects (drowsiness, nausea, constipation, physical dependence). 1, 2, 3
• Overlooking combination product ingredients when recommending higher doses, risking acetaminophen toxicity. 1, 2, 3
• Continuing antitussive therapy beyond 3 weeks without diagnostic evaluation. 1, 3
• Suppressing productive cough in conditions requiring secretion clearance. 2, 3

Adverse Effects Profile

• Dextromethorphan has a superior safety profile compared to codeine or other opioid antitussives, with no risk of physical dependence at therapeutic doses. 1, 6
• Adverse reactions are infrequent and usually not severe, predominantly including dose-related neurological, cardiovascular, and gastrointestinal disturbances. 6
• The safety profile in overdose is reassuring in both adults and children when pure dextromethorphan is involved. 6
• Adverse events occur most often with higher doses (0.60-0.94 mg/kg in children). 5