What is the weight-based dosage of dextromorphan (cough suppressant)?

Weight-Based Dosing of Dextromethorphan

For children and adolescents, dextromethorphan should be dosed at 0.5 mg/kg per dose for optimal cough suppression, with a maximum single dose of 30 mg for children under 12 years and 60 mg for adolescents and adults. 1, 2

Pediatric Dosing Algorithm

Age-Based Dosing (Standard OTC Recommendations)

• Ages 2-5 years: 7.5 mg per dose 2
• Ages 6-11 years: 15 mg per dose 2
• Ages 12-18 years: 30 mg per dose 2

Weight-Based Dosing (Optimal Approach)

The weight-based approach of 0.5 mg/kg per dose provides better symptomatic relief while minimizing adverse events compared to standard age-based dosing. 2

• Target dose: 0.5 mg/kg per dose 2
• Dosing frequency: Three to four times daily 1
• Maximum daily dose: 120 mg 1
• Maximum single dose for optimal cough suppression: 60 mg 1

Adult Dosing

For adults, the recommended dose is 10-15 mg three to four times daily, with a maximum daily dose of 120 mg. 1

• Standard dose: 10-15 mg three to four times daily 1
• Maximum cough suppression: 60 mg single dose 1
• Maximum daily dose: 120 mg 1

Critical Dosing Considerations

Standard OTC Dosing is Subtherapeutic

Standard over-the-counter dosing (15-30 mg) is often inadequate for optimal cough suppression, as maximum cough reflex suppression occurs at 60 mg. 1

Combination Product Warning

Exercise caution with higher doses when using combination products containing acetaminophen or other ingredients to avoid toxicity from co-formulated medications. 1

Dose-Response Relationship

Research demonstrates that medium-dose (0.45 to <0.60 mg/kg) and high-dose (0.60-0.94 mg/kg) dextromethorphan provide somewhat better symptomatic relief than low-dose (0.35 to <0.45 mg/kg), though adverse events occur more frequently at higher doses. 2

Safety Profile in Pediatrics

Accidental ingestions in children under 5 years are generally well-tolerated with supportive care alone, with no fatalities reported in large surveillance studies. 3, 4

• Mean dose in accidental ingestions: 2.64 mg/kg resulted in only lethargy as the primary adverse event 4
• Most common adverse events: CNS effects (ataxia) and autonomic symptoms (tachycardia) 3
• Dystonia occurs in 5.4% of overdose cases 3
• Flushing/urticarial rash occurs in 18.1% of cases 3

Practical Dosing Algorithm

Step 1: Calculate Weight-Based Dose

• Multiply patient's weight in kg by 0.5 mg/kg 2
• Round to nearest practical dose based on available formulation 5

Step 2: Apply Age-Appropriate Maximum

• Children 2-11 years: Cap single dose at 15-24.75 mg 6
• Adolescents 12-18 years: Cap single dose at 30 mg 2
• Adults: Can use up to 60 mg for maximum suppression 1

Step 3: Verify Combination Product Safety

• Check all ingredients in formulation 1
• Ensure acetaminophen or other co-ingredients remain within safe limits at calculated dose 1

Step 4: Establish Dosing Frequency

• Administer three to four times daily 1
• Ensure total daily dose does not exceed 120 mg 1

Common Pitfalls to Avoid

Do not use age-based dosing alone, as this results in substantial variability (0.35-0.94 mg/kg) in actual drug exposure. 2

Do not prescribe for productive cough where secretion clearance is beneficial. 1

Do not continue beyond short-term use (typically less than 7 days); cough persisting beyond 3 weeks requires diagnostic workup. 1

Consider non-pharmacological approaches (honey and lemon) first for benign viral cough before using dextromethorphan. 1