What is the recommended dose of Robitussin (dextromethorphan) for an adult patient with an acute cough and no significant medical history?

Recommended Dextromethorphan Dosing for Acute Cough in Adults

For an adult with acute cough and no significant medical history, use dextromethorphan 30-60 mg as needed for cough suppression, with a maximum daily dose of 120 mg (typically 10-15 mg three to four times daily). 1, 2

Optimal Dosing Strategy

Standard Dosing Regimen

• Start with 10-15 mg three to four times daily (maximum 120 mg/24 hours) for routine cough suppression 1
• The FDA-approved dosing for adults is 10 mL every 12 hours (not to exceed 20 mL in 24 hours) for extended-release formulations 3

Maximum Suppression Dosing

• For severe cough requiring maximum suppression, a single 60 mg dose provides optimal cough reflex suppression 1, 2, 4
• This dose is higher than typical over-the-counter preparations but represents the dose at which maximum efficacy occurs 1, 5
• Standard OTC dosing is often subtherapeutic and may not provide adequate relief 1, 2

Critical Dosing Considerations

Combination Product Warning

• Check all combination products carefully - many contain acetaminophen or other ingredients that could lead to toxicity at higher dextromethorphan doses 1
• Use single-ingredient dextromethorphan products when prescribing higher doses to avoid exceeding safe limits of other components 1

Duration of Treatment

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

Treatment Algorithm

First-Line Approach (Before Pharmacotherapy)

• Start with honey and lemon mixture - as effective as pharmacological treatments for benign viral cough and represents the simplest, cheapest option 1, 2, 4
• Consider voluntary cough suppression techniques through central modulation 1, 4

When to Use Dextromethorphan

• Use dextromethorphan when non-pharmacological measures are insufficient for symptom control 1
• Dextromethorphan is the preferred antitussive due to superior safety profile compared to codeine 1, 2, 4, 6
• Effective for dry, non-productive cough 2, 4

Special Situations

• For nocturnal cough disrupting sleep: Consider first-generation sedating antihistamines instead of or in addition to dextromethorphan 1, 2
• For menthol inhalation: Provides quick but brief relief and can be used adjunctively 1

When NOT to Use Dextromethorphan

Absolute Contraindications

• Do not use in patients requiring assessment for pneumonia (tachycardia, tachypnea, fever, abnormal chest examination) 2, 4
• Avoid in productive cough with significant sputum - suppression prevents necessary mucus clearance 2

Relative Contraindications

• Not recommended for routine use in acute bronchitis due to inconsistent efficacy 1
• Should not be first-line for postinfectious cough - try inhaled ipratropium first 1

Common Prescribing Pitfalls to Avoid

• Using subtherapeutic doses (less than 30 mg) that provide inadequate relief 1, 2, 4, 7
• Prescribing codeine-based products which have no efficacy advantage but significantly more adverse effects (drowsiness, nausea, constipation, dependence) 1, 2, 4
• Suppressing productive cough when secretion clearance is physiologically necessary 2
• Continuing therapy beyond 3 weeks without diagnostic evaluation 1

Evidence Supporting This Approach

• Dextromethorphan at 30 mg provides modest reduction in cough counts (19-36%) in adults with upper respiratory infections 1, 5
• A dose-response relationship exists with maximum cough reflex suppression at 60 mg 1, 2, 5
• Dextromethorphan is more effective than codeine at reducing cough intensity and is preferred by patients 6
• The 30 mg single dose showed limited efficacy in some studies, supporting the use of higher or more frequent dosing 7