What is the recommended dosing regimen for Dextromethorphan in a typical adult patient without severe underlying medical conditions?

Dextromethorphan Dosing Schedule

For adults and children 12 years and older, dextromethorphan should be dosed at 10-15 mg three to four times daily (every 6-8 hours), with a maximum daily dose of 120 mg, though maximum cough suppression occurs at 60 mg single doses. 1, 2, 3

Standard Dosing Regimen by Age

Adults and Children ≥12 Years

• 10-15 mg every 6-8 hours (three to four times daily) 1, 2
• Maximum daily dose: 120 mg 1, 2
• For bedtime dosing: 15-30 mg to suppress nocturnal cough and promote sleep 2
• FDA-approved extended-release formulation: 10 mL every 12 hours, not exceeding 20 mL in 24 hours 3

Children 6 to <12 Years

• 5 mL every 12 hours (extended-release formulation) 3
• Maximum: 10 mL in 24 hours 3

Children 4 to <6 Years

• 2.5 mL every 12 hours (extended-release formulation) 3
• Maximum: 5 mL in 24 hours 3

Children <4 Years

• Do not use 3

Critical Dosing Considerations

Dose-Response Relationship

• Standard over-the-counter doses are often subtherapeutic 1, 2
• Maximum cough reflex suppression occurs at 60 mg and can be prolonged 1, 2
• A clear dose-response relationship exists, with higher doses providing superior cough suppression 1

Combination Product Warning

• Exercise extreme caution with combination preparations containing acetaminophen or other ingredients 1, 2
• Higher doses of dextromethorphan in combination products could lead to toxic levels of additional ingredients 1, 2
• Always verify the formulation before prescribing higher doses 1, 2

When to Use Dextromethorphan

Appropriate Indications

• Dry, non-productive cough from viral upper respiratory infections 1, 4
• Postinfectious cough only after other measures (inhaled ipratropium) have failed 1
• Short-term symptomatic relief in acute bronchitis 4

Contraindications and Red Flags

• Do NOT use in suspected pneumonia with tachycardia, tachypnea, fever, or abnormal chest examination 1, 4
• Avoid in productive cough where secretion clearance is physiologically necessary 1, 4
• Do not suppress cough in asthma or COPD if it serves a protective clearance function 1

Clinical Algorithm for Scheduling

Step 1: First-Line Non-Pharmacological Approach

• Start with honey and lemon mixture, which may be as effective as pharmacological treatments 1, 2, 4
• Consider voluntary cough suppression through central modulation 1, 2

Step 2: Pharmacological Treatment

• If non-pharmacological measures fail, initiate dextromethorphan 10-15 mg every 6-8 hours 1, 2
• For severe symptoms requiring maximum suppression, consider 60 mg single dose (verify no combination ingredients) 1, 2

Step 3: Nocturnal Cough Management

• Add bedtime dose of 15-30 mg if cough disrupts sleep 2
• Alternatively, consider first-generation sedating antihistamines for nocturnal cough 1, 2, 4

Step 4: Duration and Reassessment

• Use for short-term symptomatic relief only 2
• Discontinue if no improvement after short course 2
• If cough persists beyond 3 weeks, stop antitussive therapy and perform full diagnostic workup 2, 4

Critical Pitfalls to Avoid

• Using subtherapeutic doses (<60 mg for maximum effect) may provide inadequate relief 1, 2, 4
• Prescribing codeine-based products, which have no efficacy advantage over dextromethorphan but significantly more adverse effects (drowsiness, nausea, constipation, physical dependence) 1, 2, 4
• Suppressing productive cough in pneumonia or bronchiectasis where clearance is essential 1, 4
• Continuing therapy beyond 3 weeks without investigating underlying causes 2, 4
• Missing serious conditions like hemoptysis, breathlessness, or foreign body aspiration before treating symptomatically 1

Safety Profile Advantages

• Superior safety compared to codeine or pholcodine with fewer adverse effects 1, 2, 5
• No risk of physical dependence at therapeutic doses 2
• No dose adjustment required in chronic kidney disease as it is hepatically metabolized via CYP2D6, not renally excreted 2
• Safe even in overdose at therapeutic ranges 5

Special Populations

Renal Impairment

• No dose adjustment necessary for patients with chronic kidney disease 2
• Primarily metabolized hepatically by CYP2D6, not renally excreted 2

Abuse Potential Warning

• At inappropriately high doses (>1500 mg/day), dextromethorphan can induce PCP-like psychosis with delusions, hallucinations, and paranoia 6
• Not detected on standard urine drug screens 6