What are the commonly prescribed antihistamines in New Zealand?

Commonly Prescribed Antihistamines in New Zealand

In New Zealand, the commonly prescribed antihistamines include fexofenadine, loratadine, cetirizine, and desloratadine, with second-generation non-sedating antihistamines being the preferred options for most patients. 1, 2

Second-Generation Antihistamines (Preferred)

These are the first-line options due to their favorable safety profile and minimal sedative effects:

• Fexofenadine (180mg) - Non-sedating even at higher doses, no performance impairment 1, 2, 3
• Loratadine (10mg) - Non-sedating at recommended doses 1, 2
• Desloratadine - Non-sedating at recommended doses 1
• Cetirizine (10mg) - Mildly sedating, may cause drowsiness in some patients 1, 2

First-Generation Antihistamines (Limited Use)

These are used less frequently due to their sedative and anticholinergic effects:

• Chlorphenamine (chlorpheniramine) - Sedating, used primarily for acute allergic reactions or when sedation is desired 1
• Hydroxyzine - Highly sedating, typically reserved for nighttime use or short-term treatment 1
• Diphenhydramine - Sedating, used primarily for sleep or acute allergic reactions 2

Clinical Decision-Making Algorithm

1. For most patients with allergic conditions:

   • Start with a second-generation antihistamine (fexofenadine, loratadine)
   • These provide effective symptom control with minimal sedation 1, 3

2. For elderly patients:

   • Avoid first-generation antihistamines due to increased risk of falls, cognitive impairment, and anticholinergic effects 1
   • Use fexofenadine or loratadine at standard doses 1

3. For patients with daytime symptoms requiring alertness:

   • Use fexofenadine (preferred) or loratadine 1, 3
   • Avoid cetirizine if sedation is a concern 1

4. For patients with nighttime symptoms or sleep disturbance:

   • Consider adding a first-generation antihistamine at night only 1
   • Example: daytime non-sedating + nighttime sedating antihistamine

5. For refractory symptoms:

   • Increase dose of second-generation antihistamine up to 4 times the standard dose 2
   • Consider combination therapy with H2 antagonists (e.g., cimetidine) 1, 2

Important Clinical Considerations

• Sedation risk: First-generation antihistamines significantly impair cognitive function, driving ability, and work performance 1, 3, 4

• Dosing adjustments: Reduce doses in renal impairment, particularly for cetirizine and levocetirizine 1

• Pregnancy considerations: Avoid all antihistamines if possible, especially in the first trimester; chlorphenamine has the longest safety record if treatment is necessary 1

• Pediatric use: Second-generation antihistamines are generally safe for children over 12 years; consult product information for younger children 1, 5

• Drug interactions: Second-generation antihistamines have fewer drug interactions than first-generation options 6

Common Pitfalls to Avoid

1. Prescribing first-generation antihistamines for daytime use - These cause significant sedation and impair performance, even when patients don't feel drowsy 1, 4

2. Prescribing sedating antihistamines to elderly patients - This increases fall risk and can worsen cognitive function 1

3. Assuming all second-generation antihistamines are equally non-sedating - Cetirizine has more sedative potential than fexofenadine or loratadine 1, 3

4. Underdosing in refractory cases - For difficult-to-control symptoms, increasing the dose of second-generation antihistamines (up to 4x standard dose) may be more effective than adding other medications 2