Antihistamines
First-generation antihistamines, including hydroxyzine, have been used as antiemetics in pregnant women. Hydroxyzine is generally considered safe, but should be discussed carefully, as it carries a slightly increased risk of congenital malformations (5.8% vs. 2.3% background risk).
Newborns exposed to large doses of hydroxyzine (150 mg or more daily) have also exhibited withdrawal symptoms at birth, including irritability, poor feeding, and tonic-clinic seizures.
“Antihistamines can exert oxytocin-like effects, especially in overdose or when given intravenously, so please avoid using them in the last month of pregnancy. There have also been a few reports of retrolental fibroplasia in preterm infants who were exposed to antihistamines within 2 weeks of delivery,” Dr. Murase said.