What is the most effective treatment for an adult patient with chronic cough, potentially of allergic origin?

Treatment of Chronic Cough with Potential Allergic Origin

For an adult with chronic cough potentially of allergic origin, initiate a first-generation antihistamine/decongestant combination (such as dexbrompheniramine plus sustained-release pseudoephedrine) as first-line therapy, with intranasal corticosteroids added immediately if allergic rhinitis is confirmed. 1, 2

Initial Diagnostic Approach

Before treating, determine if this is truly unexplained chronic cough or if there's an identifiable allergic cause:

• Chronic cough is defined as persisting longer than 8 weeks 3
• Look for specific features suggesting allergic rhinitis: nasal discharge, throat clearing, sensation of postnasal drainage, and cobblestone appearance of the oropharyngeal mucosa 1
• Approximately 20% of patients have "silent" postnasal drip with no obvious upper airway symptoms yet still respond to treatment directed at the upper airway 1
• Obtain a chest radiograph as the first-line investigation to rule out other pathology 4

Treatment Algorithm for Allergic Chronic Cough

First-Line Therapy

Start immediately with combination therapy rather than sequential monotherapy:

• First-generation antihistamine/decongestant combination is the most effective evidence-based treatment 3, 1

  • Specific effective combinations include dexbrompheniramine maleate plus sustained-release pseudoephedrine sulfate, or azatadine maleate plus sustained-release pseudoephedrine sulfate 1
  • First-generation antihistamines are superior to newer non-sedating antihistamines due to their anticholinergic properties that directly suppress cough 1, 2
  • Newer-generation antihistamines (like cetirizine, loratadine) are ineffective for non-allergic causes of postnasal drip cough 1

• Add intranasal corticosteroids immediately for confirmed allergic rhinitis: fluticasone 100-200 mcg daily for a 1-month trial 1, 2

  • For moderate-to-severe allergic rhinitis, the combination of intranasal fluticasone plus intranasal azelastine provides 40% superior symptom reduction compared to monotherapy 2

Dosing Strategy to Minimize Side Effects

• Start with once-daily dosing at bedtime for the first few days to minimize sedation, then increase to twice-daily therapy as tolerated 1
• Common side effects include: dry mouth, transient dizziness, insomnia, urinary retention, jitteriness, tachycardia, and worsening hypertension 1
• Monitor blood pressure after initiating decongestant therapy, as decongestants can worsen hypertension 1

Expected Timeline for Response

• Most patients will see improvement within days to 2 weeks of initiating therapy 1
• Complete resolution may take several weeks to a few months 1
• If no response after 1-2 weeks with the antihistamine-decongestant combination, add or optimize intranasal corticosteroids 1

Alternative and Adjunctive Therapies for Allergic Cough

If Contraindications to Decongestants Exist

• Ipratropium bromide nasal spray (42 mcg per spray, 2 sprays per nostril 4 times daily) provides anticholinergic drying effects without systemic cardiovascular side effects 1, 2
• This is particularly useful in patients with hypertension, obesity, or other cardiovascular contraindications to oral decongestants 1

Additional Options for Allergic Rhinitis

• Oral leukotriene inhibitors (such as montelukast 10 mg daily) decrease symptoms of allergic rhinitis but are less effective than intranasal corticosteroids 1, 2
• Nasal cromolyn can be used as an alternative first-line agent for allergic rhinitis-related cough 2
• High-volume saline nasal irrigation (150 mL) improves outcomes through mechanical removal of mucus and allergens 1

If Cough Persists Despite Adequate Upper Airway Treatment

Sequential Evaluation for Other Causes

After 2 weeks of adequate treatment without response, proceed with evaluation for other common causes 3, 1:

1. Test for bronchial hyperresponsiveness and eosinophilic bronchitis, or conduct a therapeutic corticosteroid trial 3

   • A 2-week oral steroid trial can help determine if cough is due to eosinophilic airway inflammation 3
   • Cough is unlikely to be due to eosinophilic airway inflammation if there is no response to this trial 3

2. Evaluate for gastroesophageal reflux disease (GERD) if clinical profile suggests it 1

   • Initiate empiric therapy with proton pump inhibitor (omeprazole 20-40 mg twice daily before meals) for at least 8 weeks plus dietary modifications 1
   • Improvement in cough from GERD treatment may take up to 3 months 1
   • However, in patients with unexplained chronic cough and a negative workup for GERD, proton pump inhibitor therapy should not be prescribed 3

3. Consider asthma or non-asthmatic eosinophilic bronchitis 3, 1

   • Bronchial provocation testing should be performed in patients without a clinically obvious etiology with normal spirometry 3

Treatment for Truly Unexplained Chronic Cough

If cough remains unexplained after guideline-based assessment and therapeutic trials:

Speech Pathology Therapy

• Multimodality speech pathology therapy is suggested as a therapeutic trial for unexplained chronic cough (Grade 2C) 3

Pharmacologic Options

• Gabapentin can be considered with careful risk-benefit discussion 3

  • Dose escalation schedule: begin at 300 mg once daily, adding doses each day as tolerated up to maximum 1,800 mg daily in two divided doses 3
  • Reassess risk-benefit profile at 6 months before continuing 3

• Inhaled corticosteroids should NOT be prescribed in patients with negative tests for bronchial hyperresponsiveness and eosinophilia (Grade 2B) 3

Critical Pitfalls to Avoid

• Never use topical nasal decongestants (oxymetazoline, xylometazoline) for more than 3-5 consecutive days due to risk of rhinitis medicamentosa (rebound congestion) 1
• Do not discontinue partially effective treatments prematurely - maintain all therapies that provide some benefit, as upper airway cough syndrome, asthma, and GERD together account for approximately 90% of chronic cough cases 1
• Do not assume purulent nasal discharge indicates bacterial infection requiring antibiotics - yellowish-green discharge is typical of viral infections 1
• Monitor for increased intraocular pressure in glaucoma patients taking first-generation antihistamines 1
• Recognize that approximately 20% of patients have "silent" postnasal drip with no obvious symptoms, so consider empiric treatment even without classic upper airway symptoms 1