What is the maximum daily dosing of dextromethorphan (cough suppressant)?

Maximum Daily Dosing of Dextromethorphan

The maximum daily dose of dextromethorphan is 120 mg for adults and children 12 years and older, with dosing divided throughout the day. 1, 2

Age-Specific Maximum Daily Doses

Adults and Children ≥12 Years

• Maximum: 120 mg per 24 hours 1
• Standard dosing: 10-15 mg three to four times daily 1
• Extended-release formulations: 10 mL (60 mg) every 12 hours, not exceeding 20 mL (120 mg) in 24 hours 2

Children 6 to <12 Years

• Maximum: 10 mL (60 mg) in 24 hours 2
• Extended-release dosing: 5 mL every 12 hours 2

Children 4 to <6 Years

• Maximum: 5 mL (30 mg) in 24 hours 2
• Extended-release dosing: 2.5 mL every 12 hours 2

Children <4 Years

• Do not use 2

Clinical Context and Dosing Considerations

Standard over-the-counter dosing is often subtherapeutic for optimal cough suppression. 1 Maximum cough reflex suppression occurs at 60 mg single doses, which is higher than typical OTC recommendations but still within the 120 mg daily maximum. 1

Optimal Therapeutic Dosing

• For effective cough suppression, 60 mg provides maximum reflex suppression 1
• This can be achieved with a single 60 mg dose or divided dosing totaling up to 120 mg daily 1
• Research suggests doses of 0.5 mg/kg may balance symptomatic relief with adverse event avoidance in pediatric patients 3

Critical Safety Warnings

Exercise caution with combination products containing dextromethorphan plus other ingredients like acetaminophen. 1 When using higher doses approaching the 120 mg maximum, verify that combination preparations do not result in excessive doses of other active ingredients. 1

Drug Interactions

• Use with extreme caution in patients taking MAO inhibitors or other serotonergic agents 4
• The dextromethorphan/quinidine combination requires special precaution in elderly patients due to increased fall risk and drug interactions 4

Contraindications

• Do not use for productive cough where secretion clearance is beneficial 1, 4
• Avoid in patients with compromised hepatic or renal function without dose adjustment 5

Duration of Treatment

Dextromethorphan should be used for short-term symptomatic relief only. 1 If cough persists beyond 3 weeks, discontinue antitussive therapy and pursue full diagnostic workup for alternative diagnoses. 1

Common Prescribing Pitfalls

• Underdosing: Standard OTC doses may not provide adequate cough suppression; consider doses up to 60 mg for maximum effect while staying within the 120 mg daily limit 1
• Overlooking combination products: Always verify total daily doses of all ingredients in multi-drug formulations 1
• Prolonged use: Continuing dextromethorphan beyond short-term symptomatic treatment delays appropriate diagnostic evaluation 1
• Inappropriate patient selection: Using in productive cough or without ruling out serious underlying causes 1, 4