What is the recommended dose and contraindications for Dextromethorphan (cough suppressant) in adults?

Dextromethorphan Dosing and Contraindications

For adults with acute dry cough, dextromethorphan should be dosed at 30-60 mg every 12 hours (maximum 120 mg daily) rather than standard over-the-counter doses, which are typically subtherapeutic. 1, 2, 3

Recommended Dosing

Standard Adult Dosing

• Optimal dose: 30-60 mg every 12 hours 1, 2, 3
• Maximum daily dose: 120 mg 3
• Maximum cough suppression occurs at 60 mg single dose with prolonged effect 1, 2
• Standard over-the-counter dosing (10-15 mg) is often subtherapeutic and may not provide adequate relief 1, 3

FDA-Approved Dosing (Extended-Release Formulations)

• Adults and children ≥12 years: 10 mL every 12 hours, not exceeding 20 mL in 24 hours 4
• Children 6 to <12 years: 5 mL every 12 hours, not exceeding 10 mL in 24 hours 4
• Children 4 to <6 years: 2.5 mL every 12 hours, not exceeding 5 mL in 24 hours 4
• Children <4 years: Do not use 4

Dose-Response Relationship

• A clear dose-response relationship exists, with 60 mg providing maximum cough reflex suppression 1, 2
• The effect at 60 mg can be prolonged compared to lower doses 1, 2

Contraindications and Clinical Scenarios Requiring Caution

Absolute Contraindications

• Patients requiring assessment for pneumonia (tachycardia, tachypnea, fever, abnormal chest examination) must have pneumonia ruled out first before using dextromethorphan 1
• Productive cough where secretion clearance is beneficial should not be suppressed with dextromethorphan 3

Relative Contraindications and Cautions

• Combination preparations containing acetaminophen or other ingredients: Exercise caution with higher doses to avoid excessive intake of additional ingredients 1, 2, 3
• Cough lasting >3 weeks: Requires full diagnostic workup rather than continued antitussive therapy 3
• Cough with increasing breathlessness: Assess for asthma or anaphylaxis before treating 1
• Cough with fever, malaise, purulent sputum: May indicate serious lung infection requiring specific treatment 1
• Significant hemoptysis or possible foreign body inhalation: Requires specialist referral 1

Limited Efficacy Scenarios

• Acute cough due to upper respiratory infection: Central cough suppressants including dextromethorphan have limited efficacy and are not routinely recommended for this indication 1, 3
• Acute bronchitis: Evidence is inconsistent, and dextromethorphan is not recommended for routine use 3

Clinical Algorithm for Use

First-Line Approach

• Start with simple home remedies (honey and lemon) as they may be as effective as pharmacological treatments for benign viral cough 1, 3
• Consider voluntary cough suppression techniques, which may reduce cough frequency through central modulation 1, 3

When Pharmacological Treatment Is Needed

• Use dextromethorphan 30-60 mg if non-pharmacological measures are insufficient 1, 2, 3
• For nocturnal cough specifically, consider first-generation sedating antihistamines instead 1, 3
• For postinfectious cough, try inhaled ipratropium before dextromethorphan 3

Treatment Failure Management

• Discontinue dextromethorphan if no improvement after a short course 3
• For severe paroxysms of postinfectious cough, consider prednisone 30-40 mg daily for a short period 3
• For opioid-resistant cough, consider peripherally-acting antitussives or nebulized lidocaine as last resort 3

Important Safety Considerations

Advantages Over Alternatives

• Dextromethorphan is preferred over codeine or pholcodine because it has equivalent efficacy but a significantly better safety profile with fewer adverse effects (less drowsiness, nausea, constipation, and no physical dependence) 1, 2, 3

Common Pitfalls to Avoid

• Using subtherapeutic doses: Standard OTC doses may not provide adequate cough suppression 1, 3
• Overlooking combination products: Always check for additional ingredients like acetaminophen when prescribing higher doses 1, 2, 3
• Prescribing for productive cough: Dextromethorphan should not suppress cough when secretion clearance is needed 3
• Continuing treatment beyond 3 weeks: Persistent cough requires diagnostic evaluation, not continued antitussive therapy 3
• Not considering underlying causes: GERD, upper airway symptoms, or asthma may require specific treatment rather than cough suppression 1

Duration of Treatment

• Use for short-term symptomatic relief only 3
• Reassess if cough persists beyond the expected 1-3 week self-limiting course 1