What is the proper dosage and usage of Robitussin (dextromethorphan) for cough relief?

Robitussin (Dextromethorphan) Dosing and Usage for Cough Relief

Recommended Dosing

For optimal cough suppression in adults, use dextromethorphan 30-60 mg, with maximum cough reflex suppression occurring at 60 mg—significantly higher than standard over-the-counter dosing which is often subtherapeutic. 1

Adult Dosing (≥12 years)

• Standard dose: 10-15 mg three to four times daily 1
• Maximum single dose: 60 mg for severe cough 1, 2
• Maximum daily dose: 120 mg 1
• FDA-approved OTC dosing: 10 mL every 12 hours (not to exceed 20 mL in 24 hours) 3

Pediatric Dosing

• Ages 6 to <12 years: 5 mL every 12 hours (maximum 10 mL in 24 hours) 3
• Ages 4 to <6 years: 2.5 mL every 12 hours (maximum 5 mL in 24 hours) 3
• Under 4 years: Do not use 3
• Important caveat: Evidence for dextromethorphan efficacy in children is minimal to absent, with studies showing no difference from placebo 4, 5

When to Use Dextromethorphan

First-Line Indications

Start with simple home remedies like honey and lemon before considering dextromethorphan, as these may be equally effective for benign viral cough. 1, 6

• Dry, non-productive cough interfering with daily activities or sleep 6, 7
• Postinfectious cough only after inhaled ipratropium has failed 1, 6
• Acute bronchitis for short-term symptomatic relief 1, 2

When NOT to Use

• Productive cough where secretion clearance is beneficial 1, 2
• Cough with fever, purulent sputum, or signs of pneumonia (tachycardia, tachypnea, abnormal chest exam)—rule out serious infection first 6
• Children under 4 years 3
• Cough lasting >3 weeks—requires full diagnostic workup rather than continued antitussive therapy 1

Treatment Algorithm

Step 1: Non-Pharmacological Approaches

• Honey and lemon mixtures 1, 6
• Voluntary cough suppression techniques 1, 6

Step 2: Pharmacological Options

• Dextromethorphan 30-60 mg for additional daytime relief 1, 6
• First-generation antihistamines (e.g., diphenhydramine) specifically for nocturnal cough due to sedative properties 1, 6
• Menthol inhalation for quick but temporary relief 1, 6

Step 3: Alternative Agents if Dextromethorphan Fails

• Inhaled ipratropium for postinfectious cough 1, 2
• Short-course prednisone (30-40 mg daily) for severe paroxysms of postinfectious cough 1, 6
• Peripheral antitussives (levodropropizine, moguisteine) for opioid-resistant cough 1, 2

Critical Safety Considerations

Avoid Combination Products at Higher Doses

Exercise caution with higher doses of dextromethorphan as many combination preparations contain acetaminophen or other ingredients that can reach toxic levels. 1, 2

Why NOT Codeine

Codeine has no greater efficacy than dextromethorphan but carries significantly more adverse effects including drowsiness, nausea, constipation, and physical dependence. 1, 6, 2

Abuse Potential

• Dextromethorphan has documented recreational abuse potential, particularly in teenagers 8
• Monitor for substance dependence syndrome with prolonged use 8

Common Pitfalls to Avoid

1. Using subtherapeutic doses: Standard OTC dosing (15-30 mg) may not provide adequate relief; consider 60 mg for maximum effect 1, 2

2. Prescribing for children based on adult evidence: Dextromethorphan shows no benefit over placebo in pediatric studies 4, 5

3. Continuing beyond 3 weeks: Persistent cough requires diagnostic evaluation, not continued suppression 1

4. Using for productive cough: Suppressing a productive cough impairs necessary secretion clearance 1, 2

5. Choosing codeine over dextromethorphan: No efficacy advantage with substantially worse side effect profile 1, 6, 2