What is the next step in managing a patient with a persistent dry cough not relieved by dextromethorphan (cough suppressant), considering potential underlying conditions such as asthma or chronic obstructive pulmonary disease (COPD)?

Management of Dry Cough Unresponsive to Dextromethorphan

When dextromethorphan fails to control a dry cough, pursue a systematic diagnostic and treatment algorithm targeting the three most common causes: upper airway cough syndrome (UACS), asthma, and gastroesophageal reflux disease (GERD), in that specific order. 1

Step 1: Initiate Treatment for Upper Airway Cough Syndrome (UACS)

• Start a first-generation antihistamine/decongestant combination (such as brompheniramine with sustained-release pseudoephedrine) as the initial empiric therapy. 1, 2, 3
• First-generation antihistamines are specifically required—newer non-sedating antihistamines are ineffective for UACS-related cough. 3
• Expect initial improvement within 1-2 weeks, though complete resolution may require several weeks of continuous therapy. 2, 3

Step 2: If Inadequate Response, Add Asthma Treatment

• After 2-4 weeks without adequate response to UACS treatment, initiate inhaled corticosteroids (ICS) combined with long-acting β-agonists (LABA), such as fluticasone/salmeterol twice daily. 1, 2
• The medical history alone is unreliable for diagnosing asthma as a cause of cough. 1
• Ideally, perform bronchoprovocation challenge (BPC) if spirometry does not show reversible airflow obstruction; if BPC is unavailable, proceed with empiric antiasthma therapy. 1
• Monitor for response within 2-4 weeks. 2, 3
• Critical pitfall: Do not discontinue UACS treatment when adding asthma therapy, as multiple conditions frequently coexist and contribute simultaneously to chronic cough. 3

Step 3: If Still Inadequate Response, Add GERD Treatment

• Initiate proton pump inhibitor (PPI) therapy with dietary modifications for patients with incomplete response to UACS and asthma treatments. 1, 2, 3
• Continue all previous treatments that provided partial benefit, as chronic cough is often multifactorial. 2, 3
• Allow 1-3 months to assess response to GERD therapy, as improvement is typically slower than with UACS or asthma treatment. 2, 3

Step 4: Consider Non-Asthmatic Eosinophilic Bronchitis (NAEB)

• If diagnoses of UACS and asthma have been eliminated or treated without cough resolution, perform induced sputum testing for eosinophils. 1
• If induced sputum testing cannot be performed, administer an empiric trial of oral corticosteroids. 1

Step 5: Alternative Antitussive Agents for Refractory Cases

When systematic treatment of underlying causes fails, consider alternative cough suppressants:

• Low-dose morphine (slow-release preparation) has demonstrated efficacy for idiopathic chronic cough, though it should be reserved for severe cases due to side effect profile. 1, 4
• Gabapentin has case report evidence of success in chronic cough refractory to standard treatments. 1, 5, 4
• Baclofen or nebulized local anesthetics (lidocaine, mepivicaine) have weak evidence but may be considered. 1
• Codeine has limited efficacy and was shown ineffective in controlled studies of COPD-related cough. 5, 4

Critical Considerations

• Discontinue ACE inhibitors if the patient is taking one, as this can resolve cough within days to 2 weeks (median 26 days). 3
• Strongly advise smoking cessation, as 90% of patients with chronic bronchitis will have cough resolution after quitting. 3
• Obtain a chest radiograph to rule out significant pathology such as pneumonia, pulmonary embolism, or lung cancer. 2
• Use sequential and additive therapy rather than substituting one treatment for another, as multiple conditions often contribute simultaneously. 3

When to Refer to a Cough Specialist

• Refer patients whose cough persists despite sequential trials of therapy for UACS, asthma, and GERD. 1, 2
• Specialist cough clinics provide improved patient outcomes compared to general respiratory clinics and offer access to advanced diagnostic testing and novel therapies. 1