Which H1 antihistamine is preferred in a pregnant woman in the first trimester suffering from allergic rhinitis, and why?
- A Chlorpheniramine (chlorphenamine); first-generation, most safety data, Category B in most guidelines ✓
- B Cetirizine; Category B, minimal teratogenic data
- C Fexofenadine; Category C, longest clinical safety record
- D Loratadine; only antihistamine with FDA Category A rating in pregnancy
Correct answer: A. Chlorpheniramine (chlorphenamine); first-generation, most safety data, Category B in most guidelines
Explanation
Chlorpheniramine (a first-generation alkylamine H1 antagonist) has the most extensive safety data in pregnancy due to decades of use, and is generally classified as acceptable in the first trimester. Second-generation antihistamines (cetirizine, loratadine) are also considered relatively safe but have less longitudinal human data from the first trimester. Fexofenadine is category C. No antihistamine holds FDA Category A as no adequate controlled studies in pregnant women have established complete safety.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.