Dear Editor 
The prevalence of allergic disorders has been on the rise for decades. Allergic diseases such as chronic urticaria affect various aspects of a patient’s quality of life. Outdoor and indoor allergens can aggravate symptoms in patients with allergies [1-3].
H1-antihistamines have been available for decades, with some being accessible over the counter. The first-generation H1-antihistamines have anticholinergic and sedative effects. Basically, their use (H1 blockers) is not recommended for the routine management of allergic diseases. However, second-generation H1-antihistamines (bilastine, cetirizine, desloratadine, ebastine, fexofenadine, levocetirizine, loratadine, and rupatadine) exhibit minimal or no sedative effects and lack anticholinergic property. About 10%–15% of pregnant women use antihistamines during pregnancy. 
It is advisable to either refrain from using antihistamines or use the lowest effective dose in the first trimester of pregnancy. If necessary, we can use the recommended category A and category B antihistamines with a standard dose. Cetirizine, loratadine, chlorpheniramine, and diphenhydramine compose pregnancy category B drugs. Category A and category B drugs are safe to use. However, category C drugs should be considered case by case based on the US Food and Drug Administration (FDA).
The recommended doses for certain antihistamines are as follows: Chlorpheniramine at 4 mg q 4-6 h, loratadine at 10 mg daily, and cetirizine at 10 mg daily. 
Further studies are required to determine the safety of levocetirizine (category B) and fexofenadine (category C) in pregnancy [4]. However, desloratadine and fexofenadine are safe in pregnancy [5]. 
Intranasal antihistamines (azelastine and olopatadine) are recommended in pregnancy due to a lack of human data [6]. 
Second-generation antihistamines (cetirizine and loratadine) are usually recommended for treating allergic rhinitis during pregnancy [7]. Conversely, diphenhydramine, hydroxyzine, and ketotifen are the first generation of antihistamines that are not recommended in pregnancy despite no evidence of teratogenicity. 
Chlorpheniramine (first-generation antihistamines) and the second (new) generation H1 antihistamines (cetirizine and loratadine) are usually recommended [6]. 
Chlorpheniramine, loratadine, and cetirizine may be preferred in allergic conditions [8].
The Table 1 lists the categories of antihistamines in pregnancy.


Non-sedating antihistamines are advised in pregnant women and nursing mothers [9]. 
All H1-antihistamines are excreted in breast milk in low concentrations, but loratadine and fexofenadine display minimal excretion into breast milk. To date, there have been no reports of birth defects in women taking second-generation antihistamines during pregnancy. Second-generation antihistamines, such as loratadine and cetirizine, are preferred for breastfeeding women [10]. The use of desloratadine could be safe during pregnancy [11], but there is inadequate data on the newest antihistamines (bilastine, rupatadine) to recommend their use during pregnancy [12].
In general, both first-generation antihistamines (chlorpheniramine, diphenhydramine, and hydroxyzine) and second-generation antihistamines (loratadine, cetirizine, and fexofenadine) are considered safe during pregnancy without considerable side effects [13].

Conclusion 
First-generation H1-antihistamines, except for chlorpheniramine, should be avoided in pregnant and breastfeeding women. Second-generation H1-antihistamines, especially loratadine and cetirizine, are recommended in pregnancy. Caution should be exercised in increasing doses of antihistamines in pregnancy. 



References

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