Screening Approach for Antihistaminic Drugs

Patient-Specific Considerations

• The American Academy of Allergy, Asthma, and Immunology recommends that second-generation antihistamines should be prioritized over first-generation agents due to their superior safety profile, particularly for older adults, patients with renal or hepatic impairment, and children 1
• For older adults, second-generation antihistamines (fexofenadine, loratadine, desloratadine) are strongly preferred due to less sedation and fewer anticholinergic effects 1
• No currently licensed antihistamines are contraindicated in children 12 years and older, but dosing and age restrictions vary for younger children 2
• Acrivastine should be avoided in moderate renal impairment (creatinine clearance 10-20 mL/min) 2
• Cetirizine, levocetirizine, and hydroxyzine doses should be halved in moderate renal impairment 2, 1
• Cetirizine, levocetirizine, and alimemazine should be avoided in severe renal impairment (creatinine clearance <10 mL/min) 2
• Loratadine and desloratadine should be used with caution in severe renal impairment 2
• Mizolastine is contraindicated in significant hepatic impairment 2
• Alimemazine should be avoided due to hepatotoxicity risk 2
• Chlorphenamine and hydroxyzine should be avoided in severe liver disease due to inappropriate sedating effects 2, 1
• Best to avoid all antihistamines in pregnancy, especially during first trimester 2
• Hydroxyzine is specifically contraindicated during early pregnancy 2, 3
• Chlorphenamine is often chosen when antihistamine therapy is necessary due to long safety record 2
• Loratadine and cetirizine are FDA Pregnancy Category B drugs 2

Efficacy and Safety Screening

• Doxepin has useful antihistaminic properties but has sedating and anticholinergic side effects 2
• May be appropriate for nighttime use when sedation is beneficial for sleep 3

Screening for Potential Adverse Reactions

• First-generation antihistamines have high sedation potential that can persist longer than plasma levels 1
• Performance impairment can occur without subjective awareness of drowsiness 1
• First-generation antihistamines have significant anticholinergic effects (dry mouth, dry eyes, constipation, urinary retention) 1
• These effects are particularly problematic in older adults and those with narrow-angle glaucoma 1

Screening Algorithm for Antihistamine Selection

• Determine if antihistamine is truly necessary for the patient's condition 1
• Screen for patient-specific risk factors (age, renal/hepatic function, pregnancy status) 2, 1
• For nighttime use when sedation is beneficial, consider first-generation antihistamines 3
• For patients with renal or hepatic impairment, adjust selection based on specific contraindications 2, 1
• Monitor for adverse effects including sedation, falls, confusion, dry mouth, constipation, and urinary retention 1

Special Considerations for Allergic Testing

• Antihistamines with anti-histamine activity must be discontinued a few days before skin testing 4
• Pre-treatment with antihistamines will not reduce the severity of anaphylaxis 5
• There is no evidence supporting the use of H2-blocking drugs in immediate management of anaphylaxis 5