What is the appropriate dose of dextromethorphan for cough suppression in adults and children, including maximum daily limits and contraindications?

Dextromethorphan Dosing for Cough Suppression

For adults, dextromethorphan should be dosed at 30–60 mg every 6–8 hours (maximum 120 mg/day) to achieve effective cough suppression, as standard over-the-counter doses of 10–15 mg are subtherapeutic. 1, 2

Adult Dosing

Optimal Therapeutic Dose

• Maximum cough reflex suppression occurs at 60 mg per dose and can be prolonged at this level 1, 3
• The standard recommended regimen is 10–15 mg three to four times daily (every 6–8 hours), but this is often inadequate 1, 2
• For severe cough requiring maximum suppression, use 30–60 mg per dose 1, 2
• Maximum daily dose: 120 mg/day 2
• A bedtime dose of 15–30 mg may help suppress nocturnal cough and promote sleep 2

Critical Dosing Pitfall

• Doses below 30 mg are subtherapeutic and unlikely to provide meaningful cough relief 1, 2
• The dose-response relationship demonstrates that commonly prescribed over-the-counter doses fail to achieve adequate cough suppression 1, 3

Pediatric Dosing

FDA-Approved Dosing (from Drug Label)

• Ages 12 years and older: 10 mL every 12 hours (maximum 20 mL in 24 hours) 4
• Ages 6 to under 12 years: 5 mL every 12 hours (maximum 10 mL in 24 hours) 4
• Ages 4 to under 6 years: 2.5 mL every 12 hours (maximum 5 mL in 24 hours) 4
• Under 4 years: Do not use 4

Evidence-Based Considerations

• Research suggests a dose of approximately 0.5 mg/kg may balance symptomatic relief with adverse event avoidance in children 5
• Multiple-dose studies in children aged 6–11 years demonstrated 21–25% reduction in cough frequency with standard dosing 6
• Efficacy in children and adolescents remains less well-established than in adults 7

Safety Considerations and Contraindications

Combination Product Warning

• Exercise extreme caution with higher doses when using combination products containing acetaminophen or other ingredients, as 60 mg dextromethorphan doses could result in toxic levels of co-formulated drugs 1, 2
• Always verify the formulation before prescribing higher doses 2

When NOT to Use Dextromethorphan

• Do not use in patients requiring pneumonia assessment (tachycardia, tachypnea, fever, abnormal chest examination) until pneumonia is ruled out 1
• Avoid in productive cough where secretion clearance is beneficial 2
• Limited efficacy for acute cough due to upper respiratory infection 1
• Should only be used for short-term symptomatic relief, not long-term daily use 1

Drug Interactions

• Avoid concurrent use with three or more CNS-active agents (antidepressants, antipsychotics, benzodiazepines, antiepileptics, opioids) due to increased fall risk 1
• Dextromethorphan is metabolized by CYP2D6; quinidine and other CYP2D6 inhibitors significantly increase plasma levels 8

Abuse Potential

• At doses exceeding 1500 mg/day, dextromethorphan can induce PCP-like psychosis with delusions, hallucinations, and paranoia 9
• This "poor man's PCP" is not detected on standard urine drug screens 9

Clinical Algorithm for Cough Management

Step 1: Rule Out Serious Conditions

• Assess for pneumonia indicators (fever, tachypnea, tachycardia, abnormal chest exam) 1
• Evaluate for hemoptysis, increasing breathlessness, or foreign body aspiration requiring specialist referral 1

Step 2: First-Line Non-Pharmacological Approach

• Recommend honey and lemon mixture as initial treatment 1, 2
• Consider voluntary cough suppression techniques 1

Step 3: Pharmacological Treatment When Needed

• Prescribe dextromethorphan 30–60 mg every 6–8 hours (maximum 120 mg/day) 1, 2
• For nocturnal cough, consider first-generation sedating antihistamines (NOT promethazine) at bedtime 1, 2
• Menthol inhalation provides acute but short-lived relief for breakthrough symptoms 1, 2

Step 4: Duration and Reassessment

• Use for short-term symptomatic relief only 1
• If cough persists beyond 3 weeks, discontinue dextromethorphan and pursue full diagnostic workup rather than continued antitussive therapy 2

Why NOT Codeine

Codeine-containing products should be avoided entirely for cough suppression 1, 2

• Codeine provides no greater efficacy than dextromethorphan 1, 2, 3
• Codeine has a significantly worse adverse effect profile, including drowsiness, nausea, constipation, and risk of physical dependence 1, 2
• The British Thoracic Society explicitly recommends against codeine-containing antitussives 2

Special Populations

Chronic Kidney Disease

• No dose adjustment required for patients with CKD, as dextromethorphan is metabolized hepatically by CYP2D6, not renally excreted 2

COPD and Chronic Bronchitis

• Dextromethorphan is safe and recommended for short-term symptomatic relief in COPD patients 1
• Reduces cough frequency by 40–60% in chronic bronchitis, substantially more effective than in acute viral cough (which shows <20% suppression) 1
• Treat acute exacerbations with bronchodilators, antibiotics, and corticosteroids first; do not suppress cough during active purulent exacerbations 1

Postinfectious Cough

• Try inhaled ipratropium before dextromethorphan 1, 2
• Consider dextromethorphan only when other measures fail 1, 2
• For severe paroxysms, prednisone 30–40 mg daily for a short course may be indicated after ruling out other causes 1, 2