What is the recommended starting dose of dextromethorphan for cough suppression in healthy adults and children, for pseudobulbar affect (Nuedexta), and as an adjunct for major depressive disorder?

Starting Dose for Dextromethorphan

For cough suppression in adults, start dextromethorphan at 10-15 mg three to four times daily (every 6-8 hours), with a maximum daily dose of 120 mg. 1

Cough Suppression Dosing

Standard Adult Dosing

• The recommended starting dose is 10-15 mg administered three to four times daily for effective cough suppression in adults 1, 2
• A bedtime dose of 15-30 mg can help suppress nocturnal cough and promote undisturbed sleep 2
• Maximum daily dose should not exceed 120 mg 1, 2

Optimal Therapeutic Dosing

• Standard over-the-counter doses (15-30 mg) are often subtherapeutic—maximum cough reflex suppression occurs at 60 mg per dose 3, 2, 4
• For daytime cough requiring maximal suppression, 30-60 mg per dose provides optimal antitussive effect 3, 2, 4
• The dose-response relationship demonstrates that 60 mg achieves superior cough suppression compared to lower doses 3, 2

Pediatric Dosing (Ages 6-11 Years)

• Children ages 6-11 years: 15 mg per dose 5
• Research suggests 0.5 mg/kg may balance symptomatic relief with adverse event avoidance in children 5
• Multiple-dose regimens in children aged 6-11 years have demonstrated statistically significant reductions in objective cough frequency (25.5% reduction) and subjective cough severity 6

Important Safety Considerations

Combination Product Warning

• Exercise caution with combination preparations containing acetaminophen or other ingredients—higher dextromethorphan doses could lead to excessive amounts of these additional components 2, 4
• Always verify the formulation before prescribing doses above 30 mg 2

Duration and Monitoring

• Use dextromethorphan for short-term symptomatic relief only 2
• Cough persisting beyond 3 weeks requires full diagnostic workup rather than continued antitussive therapy 3, 4
• Discontinue if no improvement occurs after a short trial and consider alternative approaches 1

Clinical Algorithm for Cough Management

1. First-line non-pharmacologic approach: Recommend honey and lemon mixtures, which may be as effective as pharmacologic treatments through central modulation of the cough reflex 3, 2, 4

2. If medication needed for daytime cough: Prescribe dextromethorphan 30-60 mg per dose for adequate suppression 3, 2, 4

3. If medication needed for nighttime cough: Consider dextromethorphan 15-30 mg at bedtime OR a sedating first-generation antihistamine alone 3, 2

4. Avoid redundant antitussive combinations: Do not combine dextromethorphan with benzonatate or other antitussives, as this provides no added benefit 3

Common Pitfalls to Avoid

• Using subtherapeutic doses below 30-60 mg for maximal cough suppression—this is the most common prescribing error 3, 2, 4
• Combining multiple antitussive agents without clear rationale 3
• Prescribing promethazine-containing products for cough despite lack of supporting efficacy evidence 3
• Suppressing productive cough when airway clearance is beneficial 3
• Continuing therapy beyond 3 weeks without diagnostic evaluation 3, 4

Special Formulations

Pseudobulbar Affect (Nuedexta)

• Dextromethorphan 30 mg combined with quinidine 30 mg (fixed-dose combination) administered every 12 hours 7
• Quinidine inhibits CYP2D6 metabolism, elevating and prolonging dextromethorphan plasma levels 7
• This formulation has been repurposed from cough suppression to treat pseudobulbar affect 8

Major Depressive Disorder

• Dextromethorphan has been compounded with bupropion for treatment of major depressive disorder, representing a novel repurposing of this agent 8