Can antihistamines be used to treat allergic cough?

Antihistamines for Allergic Cough Treatment

Antihistamines are effective for treating allergic cough, with first-generation antihistamines being more effective than newer non-sedating antihistamines due to their anticholinergic properties. 1, 2

Types of Antihistamines for Allergic Cough

First-Generation Antihistamines

• First-generation antihistamines are the preferred treatment for allergic cough, particularly when combined with decongestants 1, 2
• Recommended options include:
  • Dexbrompheniramine maleate (6 mg twice daily) 2
  • Azatadine maleate (1 mg twice daily) 2
  • Brompheniramine (12 mg twice daily for adults) 2
  • Chlorpheniramine (4 mg four times daily for adults) 2
  • Diphenhydramine (25-50 mg four times daily for adults) 2

Second-Generation Antihistamines

• Second-generation antihistamines like cetirizine may be beneficial for allergic cough associated with allergic rhinitis 3, 4
• These are less effective than first-generation antihistamines for non-allergic causes of cough 1, 5
• Loratadine has shown some efficacy in treating allergic cough in patients with allergic rhinoconjunctivitis 6

Treatment Algorithm for Allergic Cough

For Allergic Rhinitis-Related Cough

1. First-line therapy options:

   • Nasal corticosteroids 1, 5
   • Antihistamines (oral or nasal) 1, 5
   • Cromolyn 1
   • Consider oral leukotriene inhibitors 1, 5

2. Antihistamine selection:

   • For allergic rhinitis: Second-generation (non-sedating) antihistamines may be effective 1, 7
   • For mixed or unclear etiology: First-generation antihistamines are preferred 1, 2

For Non-Allergic Rhinitis-Related Cough

1. First-line therapy:

   • First-generation antihistamine plus decongestant combination 1, 2, 5
   • Effective combinations include:
     • Dexbrompheniramine maleate (6 mg twice daily) plus pseudoephedrine sulfate (120 mg twice daily) 1, 2
     • Azatadine maleate (1 mg twice daily) plus pseudoephedrine sulfate (120 mg twice daily) 1, 2

2. Alternative therapy:

   • Ipratropium bromide nasal spray for patients who don't respond to antihistamine/decongestant combinations or have contraindications 1, 5

Mechanism of Action and Efficacy

• First-generation antihistamines work primarily through anticholinergic properties in Upper Airway Cough Syndrome (UACS), rather than through antihistamine effects 1, 2
• They limit secretory response to inflammatory cytokines and may limit inflammatory cell access to areas of antigen deposition 1
• Improvement typically occurs within days to 2 weeks of starting treatment 1, 2
• Studies have shown that cetirizine reduces both cough intensity and frequency in children with pollen allergy 4

Important Clinical Considerations

Dosing Strategy

• To minimize sedation from first-generation antihistamines, start with once-daily dosing at bedtime for a few days before increasing to twice-daily therapy 2, 5
• For children, appropriate dosing based on age and weight is essential 8

Side Effects and Precautions

• Common side effects of first-generation antihistamines include:
  • Sedation (primary side effect) 2
  • Dry mouth and transient dizziness 5
  • Anticholinergic effects (constipation, urinary retention) 2
• More serious side effects to monitor:
  • Insomnia, jitteriness, tachycardia 5
  • Worsening hypertension 5
  • Increased intraocular pressure in glaucoma patients 2, 5

Special Populations

• Avoid first-generation antihistamines in patients with:
  • Glaucoma 1, 2
  • Symptomatic prostatic hypertrophy 1, 2
  • Cognitive impairment 2
• Use caution in older adults due to increased sensitivity to side effects 2
• In children, second-generation antihistamines are generally preferred due to safety profile, except when anticholinergic effects are specifically desired 8

Common Pitfalls and Caveats

• Newer-generation antihistamines are less effective for non-allergic causes of postnasal drip cough 1, 5
• First-generation antihistamines can cause performance impairment even without subjective awareness of sedation 2
• Concomitant use with alcohol or other CNS depressants may enhance performance impairment 2
• For chronic rhinitis conditions, longer treatment courses may be necessary 5
• Evidence for antihistamine use in children with non-specific chronic cough is limited, and benefits must be weighed against potential adverse events 9