What are the recommended doses and usage guidelines for antitussive (anti-cough) drugs, such as dextromethorphan and codeine, for managing cough in adults?

Antitussive Drugs: Dosing and Usage Guidelines

Recommended First-Line Agent

Dextromethorphan is the recommended first-line antitussive for adults due to its superior safety profile compared to codeine, with optimal cough suppression achieved at 60 mg rather than standard over-the-counter doses. 1

Dextromethorphan Dosing

Standard Dosing Regimen

• 10-15 mg three to four times daily (maximum 120 mg/24 hours) for routine cough suppression 1
• FDA-approved dosing for adults: 10 mL every 12 hours, not exceeding 20 mL in 24 hours 2

Optimal Therapeutic Dosing

• 60 mg provides maximum cough reflex suppression and is more effective than standard over-the-counter doses 1, 3
• Standard OTC dosing (30 mg) is often subtherapeutic and may not provide adequate relief 1, 3
• A dose-response relationship exists, with peak efficacy at 60 mg 1, 3, 4

Critical Safety Consideration

• Exercise caution with higher doses (60 mg) as many combination preparations contain acetaminophen or other ingredients that could reach toxic levels 1, 3
• Always verify the formulation before recommending doses above standard OTC recommendations 1

Codeine: Not Recommended

Codeine should be avoided as it has no greater efficacy than dextromethorphan but carries a significantly worse adverse effect profile. 1, 3, 4

Why Codeine Is Inferior

• No demonstrated superiority over dextromethorphan in cough suppression 1, 3
• Causes drowsiness, nausea, constipation, and risk of physical dependence 1, 5
• Poor benefit-to-risk ratio compared to dextromethorphan 1

FDA-Approved Codeine Dosing (if unavoidable)

• Adults: 2 teaspoons (10 mL) every 4 hours, maximum 6 doses in 24 hours 6
• However, this should not be used given superior alternatives 1

Treatment Algorithm for Cough Management

Step 1: Non-Pharmacological Approaches First

• Honey and lemon mixtures are as effective as pharmacological treatments for benign viral cough and should be tried first 1, 4
• Voluntary cough suppression techniques through central modulation 1, 4

Step 2: Pharmacological Treatment

• Dextromethorphan 30-60 mg for additional relief when non-pharmacological measures fail 1
• For nocturnal cough disrupting sleep: first-generation sedating antihistamines 1, 4
• For quick but temporary relief: menthol inhalation 1, 4

Step 3: Special Situations

Postinfectious Cough

• Try inhaled ipratropium first before central antitussives 1
• Consider dextromethorphan only if ipratropium fails 1
• For severe paroxysms: prednisone 30-40 mg daily for a short course 1

Duration Considerations

• Cough lasting >3 weeks requires full diagnostic workup rather than continued antitussive therapy 1
• Dextromethorphan should be used for short-term symptomatic relief only 1

Alternative Agents for Refractory Cases

When dextromethorphan fails:

• Peripherally-acting antitussives (levodropropizine or moguisteine) for opioid-resistant cough 1, 7
• Nebulized lidocaine as a last resort for refractory cases 1

Common Pitfalls to Avoid

• Using subtherapeutic doses (standard OTC 30 mg may be insufficient) 1, 3
• Prescribing codeine-based products despite lack of efficacy advantage 1, 4
• Overlooking combination product ingredients when recommending higher dextromethorphan doses 1, 3
• Continuing antitussives beyond 3 weeks without investigating underlying causes 1
• Using dextromethorphan for productive cough where secretion clearance is beneficial 1

When NOT to Use Antitussives

• Patients requiring pneumonia assessment (tachycardia, tachypnea, fever, abnormal chest exam) 4
• Productive cough where secretion clearance is needed 1
• Cough with increasing breathlessness (assess for asthma/anaphylaxis) 4
• Significant hemoptysis or suspected foreign body 4