What is the best approach to manage a dry cough in an adult patient with no significant past medical history?

Management of Dry Cough in Adults

Initial Assessment and Duration Classification

The first critical step is determining cough duration: acute (<3 weeks), subacute (3-8 weeks), or chronic (>8 weeks), as this fundamentally changes your diagnostic and therapeutic approach. 1, 2

For Acute Dry Cough (<3 weeks)

• Most acute dry coughs are viral upper respiratory tract infections that are self-limiting and benign in patients without significant comorbidities. 1
• Over-the-counter preparations may provide symptomatic benefit, though evidence for specific pharmacological effects is limited. 1
• Simple home remedies like honey and lemon mixtures should be tried before pharmacological treatments. 3
• If using dextromethorphan, prescribe 60 mg for maximum cough reflex suppression—standard OTC doses of 15-30 mg are subtherapeutic. 3, 4
• Red flags requiring immediate investigation include hemoptysis, prominent systemic illness, suspicion of inhaled foreign body, or suspicion of lung cancer. 1
• Do not use dextromethorphan if the patient is taking an MAOI or has stopped one within the past 2 weeks. 4

For Subacute Cough (3-8 weeks)

Any cough lasting ≥2 weeks with paroxysmal episodes, post-tussive vomiting, or inspiratory whooping should be treated as pertussis with immediate azithromycin 500 mg daily for 3-5 days without waiting for laboratory confirmation. 5

• Stop any ACE inhibitor immediately regardless of temporal relationship—ACE inhibitor-induced cough can persist and typically resolves within 1-4 weeks (median 26 days) after cessation. 5, 3
• If the patient smokes, smoking cessation is first-line treatment with most coughs resolving within 4 weeks. 5
• Mandatory investigations at this stage include chest radiograph to exclude pneumonia, malignancy, tuberculosis, or structural lung disease. 5
• Trial inhaled ipratropium bromide as it may attenuate postinfectious cough. 5
• If cough persists despite ipratropium and affects quality of life, consider inhaled corticosteroids for post-viral airway inflammation. 5

For Chronic Dry Cough (>8 weeks)

Chronic dry cough requires a systematic algorithmic approach targeting the three most common causes: upper airway cough syndrome (UACS), asthma, and gastroesophageal reflux disease (GERD), which account for the vast majority of cases. 2, 6

Mandatory Initial Workup for Chronic Cough

• Chest radiograph is required for all patients to rule out malignancy, infection, or structural abnormalities. 1, 2
• Spirometry with bronchodilator response is essential to identify airflow obstruction and assess for reversibility. 1, 2
• Detailed history focusing on: timing with meals (GERD), phonation changes (GERD), postnasal symptoms (UACS), and occupational exposures. 2, 5
• Assessment of cough severity using validated tools such as cough visual analogue scores. 1, 2

Algorithmic Treatment Approach for Chronic Dry Cough

Step 1: Treat Upper Airway Cough Syndrome First

Begin with a first-generation antihistamine-decongestant combination as UACS is the most common cause, with a typical response time of at least 1-2 weeks. 2

• First-generation antihistamines like chlorpheniramine are effective, particularly for nocturnal cough, though they cause drowsiness. 3, 7

Step 2: Assess for Asthma if UACS Treatment Fails

If UACS treatment fails, proceed with bronchial provocation testing (methacholine challenge) in patients with normal spirometry, as cough-variant asthma commonly presents without airflow obstruction. 1, 2

• A negative methacholine challenge essentially excludes asthma from the differential. 2
• If methacholine testing is unavailable, a 2-week trial of oral corticosteroids (e.g., prednisone) can confirm eosinophilic airway inflammation if cough improves. 2
• Lack of response to a 2-week corticosteroid trial effectively rules out eosinophilic airway inflammation. 2

Step 3: Empiric GERD Treatment

If asthma is excluded, initiate empiric treatment for GERD as reflux-associated cough may occur without typical gastrointestinal symptoms. 2

• GERD treatment requires at least 3 months of intensive acid suppression for proper evaluation—inadequate trial periods are a common pitfall. 2
• An empiric treatment trial is preferred over diagnostic testing as the initial approach. 2

Critical Recognition: Multifactorial Cough

Chronic cough is frequently multifactorial, with patients commonly having two or even all three common diagnoses (UACS, asthma, GERD) simultaneously, and the cough will not resolve until all contributing factors are effectively treated. 2

• Maintain all partially effective treatments rather than stopping one when adding another. 5

When to Pursue Advanced Investigation

• High-resolution CT chest may be useful when other targeted investigations are normal. 1, 2
• Bronchoscopy should be undertaken if inhalation of a foreign body is suspected. 1, 2
• Consider additional workup if the patient is immunocompromised or from a tuberculosis-endemic area. 2

Symptomatic Antitussive Therapy

Symptomatic antitussive therapy should only be considered when cough interferes with quality of life and after addressing underlying causes. 8, 9

• Benzonatate 100-200 mg three to four times daily is preferred as it works peripherally without affecting blood glucose or causing sedation. 3
• Codeine or pholcodine should not be prescribed due to their adverse side effect profile (drowsiness, nausea, constipation, physical dependence) with no greater efficacy than dextromethorphan. 3, 7
• Menthol by inhalation provides acute but short-lived relief and may be used for quick temporary symptom control. 3

Common Pitfalls to Avoid

• Overlooking GERD as a cause, since reflux-associated cough may occur without typical gastrointestinal symptoms. 2
• Relying solely on spirometry to diagnose asthma, as cough-variant asthma may present with normal spirometry. 2
• Inadequate trial periods for empiric therapy, particularly for GERD which requires at least 3 months. 2
• Using antitussives indiscriminately without proper diagnosis when cough becomes chronic. 5
• Forgetting to discontinue ACE inhibitors, which cause cough in up to 16% of patients. 3

Referral Considerations

Chronic cough should only be labeled as idiopathic after thorough assessment at a specialist cough clinic. 2

• Referral to a pulmonologist is indicated if the cause is not identified after systematic evaluation. 2, 6
• For refractory chronic cough with uncertain etiology and negative evaluation for life-threatening causes, consider cough hypersensitivity syndrome managed with gabapentin or pregabalin and speech therapy. 10