What are the common antihistamines used in Perth?

Common Antihistamines Used in Perth

Second-generation antihistamines like cetirizine, loratadine, and fexofenadine are the most commonly used antihistamines in Perth due to their favorable safety profiles, once-daily dosing, and minimal sedative effects. 1, 2

Second-Generation Antihistamines

Cetirizine

• Available as 10 mg tablets for adults and children 6 years and older 3
• Provides 24-hour relief of allergic symptoms including sneezing, runny nose, itchy/watery eyes, and itchy throat/nose 3
• Has a rapid onset of action compared to other second-generation antihistamines 2
• May cause mild sedation in some patients, especially at higher doses 1
• Dose adjustments required in moderate renal impairment (half dose) and should be avoided in severe renal impairment 2, 1

Loratadine

• Non-sedating at recommended doses 4
• Once-daily dosing (typically 10 mg)
• Safe cardiovascular profile compared to older antihistamines 4
• Should be used with caution in severe renal impairment 2

Fexofenadine

• Considered non-sedating even at high doses 4
• Excellent safety profile with minimal drug interactions 4
• Developed as a safer alternative to terfenadine (which was withdrawn due to cardiac concerns) 5

First-Generation Antihistamines

While less commonly prescribed as primary therapy, these may be used in specific situations:

Diphenhydramine

• Used for acute allergic reactions and urticaria 2
• Typically dosed at 25-50 mg
• Significant sedation limits daytime use 2

Chlorphenamine (Chlorpheniramine)

• Sometimes added to nighttime regimens (4-12 mg) to help with sleep when urticaria is problematic 2
• Often chosen during pregnancy when antihistamine therapy is necessary due to its long safety record 2

Clinical Application

For Allergic Rhinitis

• Start with a second-generation antihistamine (cetirizine, loratadine, or fexofenadine)
• For moderate symptoms that don't respond adequately, consider combination therapy with oral antihistamine plus intranasal antihistamine 1
• For severe symptoms, use oral antihistamine plus intranasal antihistamine and consider adding intranasal corticosteroids 1

For Urticaria

• Begin with a second-generation antihistamine at standard dose
• If response is inadequate, increasing the dose above licensed recommendations may be considered when benefits outweigh risks 2
• Addition of H2 antihistamine may provide better control than H1 antihistamine alone in some cases 2

Special Considerations

Renal Impairment

• Cetirizine and levocetirizine: Halve dose in moderate impairment, avoid in severe impairment 2, 1
• Loratadine: Use with caution in severe renal impairment 2
• Acrivastine: Avoid in moderate renal impairment 2

Pregnancy

• Best to avoid all antihistamines if possible, especially in first trimester 2
• If necessary, chlorphenamine is often chosen due to its long safety record 2
• Loratadine and cetirizine are FDA Pregnancy Category B drugs 2

Children

• Second-generation antihistamines are preferred due to lower sedative effects 1, 6
• Cetirizine is recommended at 5 mg daily for children 4 years old 1
• For children under 6 years, consultation with a doctor is necessary before administering antihistamines 1

Pitfalls to Avoid

• Don't use first-generation antihistamines as first-line therapy due to their sedative effects, which can impair school/work performance and driving ability 4
• Avoid using H1 antihistamines as monotherapy for anaphylaxis; they should be considered adjunctive to epinephrine 2
• Be cautious with antihistamine use in elderly patients due to potential for increased sedation and anticholinergic effects 1
• Remember that antihistamines only relieve itching and urticaria; they do not relieve stridor, shortness of breath, wheezing, GI symptoms, or shock in anaphylaxis 2