What is the appropriate treatment for an adult patient with chronic cough and no significant medical history, considering potential underlying causes such as allergies, asthma, or smoking exposure?

Treatment for Chronic Cough

Begin immediately with a first-generation antihistamine/decongestant combination (such as dexbrompheniramine plus sustained-release pseudoephedrine or azatadine plus sustained-release pseudoephedrine) as the most effective first-line treatment, targeting upper airway cough syndrome (UACS), which is the most common cause of chronic cough in adults. 1, 2

Initial Mandatory Steps Before Treatment

• Discontinue ACE inhibitors immediately if the patient is taking them, as no patient with troublesome cough should continue these medications 1
• Encourage smoking cessation as it is one of the commonest causes of persistent cough and cessation leads to significant symptom remission 1
• Obtain chest radiograph and spirometry as mandatory baseline investigations to rule out serious pathology 1, 3, 4
• Assess cough severity using visual analogue scores or cough-specific quality of life questionnaires 1, 4

Systematic Treatment Algorithm

Phase 1: Treat Upper Airway Cough Syndrome (Most Common Cause)

• Start with first-generation antihistamine/decongestant combination for 1-2 weeks 1, 2
• To minimize sedation, begin with once-daily dosing at bedtime for a few days before increasing to twice-daily therapy 2
• Most patients will see improvement within days to 2 weeks 2
• Common side effects include dry mouth and transient dizziness; monitor for insomnia, urinary retention, jitteriness, tachycardia, worsening hypertension, and increased intraocular pressure in glaucoma patients 2

If no improvement after 1-2 weeks:

• Add intranasal corticosteroids (fluticasone 100-200 mcg daily) for a 1-month trial 1, 2
• Consider ipratropium bromide nasal spray (42 mcg per spray, 2 sprays per nostril 4 times daily) as an alternative for patients with contraindications to decongestants 2
• Add high-volume saline nasal irrigation (150 mL) to mechanically remove secretions 2

Phase 2: Treat Asthma/Eosinophilic Bronchitis (If UACS Treatment Fails)

• Perform bronchial provocation testing (methacholine challenge) in patients with normal spirometry to assess for bronchial hyperresponsiveness 1, 3
• If testing is unavailable, conduct a 2-week trial of oral corticosteroids (e.g., prednisone); cough is unlikely to be due to eosinophilic airway inflammation if there is no response 1, 3
• A negative methacholine test excludes asthma but does not rule out a steroid-responsive cough 1
• Initiate inhaled corticosteroids or bronchodilators based on clinical response 5, 6

Phase 3: Treat Gastroesophageal Reflux Disease (If Above Treatments Fail)

• Initiate intensive acid suppression with proton pump inhibitors (omeprazole 20-40 mg twice daily before meals) and alginates for a minimum of 3 months 1, 4
• GERD-associated cough may occur in the absence of gastrointestinal symptoms, making it a common reason for treatment failure when not considered 1
• Improvement in cough from GERD treatment may take up to 3 months 2
• Empirical treatment should be offered before oesophageal testing 1

Recognition of Multifactorial Cough

• In 92-100% of nonsmoking patients not using ACE inhibitors with normal chest radiographs, one, two, or all three conditions (UACS, asthma, GERD) explain chronic cough 1
• Maintain all partially effective treatments rather than discontinuing them prematurely, as multiple causes often coexist 2
• Treatment effects should be formally quantified using validated measures 1, 4

When to Pursue Advanced Investigation

• Consider high-resolution computed tomography if other targeted investigations are normal and empiric treatments have failed 1, 4
• Perform bronchoscopy in patients with suspected foreign body inhalation 1
• Obtain induced sputum for eosinophil count after exclusion of other common causes, as sputum eosinophilia (>3%) has important treatment implications 1
• Consider nonasthmatic eosinophilic bronchitis (NAEB), which presents with cough, eosinophilic infiltration, normal spirometry, lack of bronchial hyperresponsiveness, and responds to corticosteroid treatment 1

Specialist Referral Criteria

• Refer to a specialist cough clinic when chronic cough remains undiagnosed after systematic evaluation of UACS, asthma, eosinophilic bronchitis, and GERD 1, 4
• Chronic cough should only be considered idiopathic following thorough assessment at a specialist cough clinic 1
• For truly refractory chronic cough, consider multimodality speech pathology therapy or gabapentin (starting at 300 mg once daily with dose escalation) 2, 7, 6, 8

Critical Pitfalls to Avoid

• Never overlook "silent" presentations: UACS, asthma, and GERD can each present with cough as the only manifestation without typical associated symptoms 1, 2
• Approximately 20% of patients have "silent" postnasal drip with no obvious symptoms yet still respond to treatment 2
• Newer-generation antihistamines are ineffective for non-allergic causes of UACS; first-generation antihistamines are superior due to their anticholinergic properties 2
• Failure to consider GORD as a cause is a common reason for treatment failure 1
• Inadequate treatment duration: GERD requires at least 3 months of intensive acid suppression for proper evaluation 1
• Never use topical nasal decongestants (oxymetazoline, xylometazoline) for more than 3-5 consecutive days due to risk of rhinitis medicamentosa 2