What is the recommended dose of Delsym (dextromethorphan) for an adult patient with an acute cough and no significant medical history?

Delsym (Dextromethorphan) Dosing for Adults

For an adult with acute cough and no significant medical history, the FDA-approved dose of Delsym is 10 mL every 12 hours, not to exceed 20 mL in 24 hours, though clinical evidence suggests this standard dosing is often subtherapeutic and maximum cough suppression occurs at 60 mg doses. 1, 2

Standard FDA-Approved Dosing

• Adults and children 12 years and older: 10 mL every 12 hours, with a maximum of 20 mL in 24 hours 1
• Shake the bottle well before use and measure only with the provided dosing cup 1

Important Clinical Context: Standard Dosing May Be Subtherapeutic

• The British Thoracic Society notes that commonly prescribed over-the-counter doses of dextromethorphan are often subtherapeutic 2, 3
• A clear dose-response relationship exists, with maximum cough reflex suppression occurring at 60 mg, which can provide prolonged relief 2, 3, 4
• Standard 30 mg doses provide only modest reduction in cough counts (19-36%) in adults with upper respiratory infections 3

First-Line Approach Before Pharmacotherapy

• Simple home remedies like honey and lemon should be considered first, as they are the simplest, cheapest, and often as effective as pharmacological treatments for benign viral cough 2, 3
• Voluntary cough suppression through central modulation may be sufficient to reduce cough frequency in some patients 2, 3

When to Use Higher Doses

• For patients requiring maximum cough suppression, a single 60 mg dose can be used 2, 3
• Exercise caution with higher doses, as some combination preparations contain additional ingredients like acetaminophen that could lead to toxicity 2, 3, 4
• The American College of Chest Physicians recommends dosing at 10-15 mg three to four times daily, with a maximum daily dose of 120 mg 3

Critical Safety Considerations

• Do not use dextromethorphan in patients requiring assessment for pneumonia (characterized by tachycardia, tachypnea, fever, or abnormal chest examination findings)—pneumonia must be ruled out first 2
• Avoid suppressing productive cough where clearance of secretions is beneficial 3
• Patients taking monoamine oxidase inhibitors or selective serotonin reuptake inhibitors require careful monitoring due to risk of serotonin syndrome 5

Alternative Options for Specific Situations

• For nocturnal cough disrupting sleep: First-generation sedating antihistamines (e.g., diphenhydramine) may be more appropriate 2, 3
• For postinfectious cough: Try inhaled ipratropium before central antitussives like dextromethorphan 2, 3
• Avoid codeine-based products—they have no greater efficacy than dextromethorphan but significantly more adverse effects including drowsiness, nausea, constipation, and physical dependence 2, 3, 4

Duration of Treatment

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

Red Flags Requiring Immediate Medical Evaluation

• Hemoptysis, breathlessness, or tachypnea 2
• Cough with increasing breathlessness (assess for asthma or anaphylaxis) 2
• Cough with fever, malaise, or purulent sputum (may indicate serious lung infection) 2