Are cefuroxime, N‑acetylcysteine, and cetirizine safe to use during the third trimester of pregnancy?

Safety of Cefuroxime, N-Acetylcysteine, and Cetirizine in Third Trimester

All three medications—cefuroxime, N-acetylcysteine, and cetirizine—are safe to use during the third trimester of pregnancy based on current evidence.

Cefuroxime (Cephalosporin Antibiotic)

Cefuroxime is compatible with use throughout pregnancy, including the third trimester 1. The 2020 ERS/TSANZ guidelines explicitly classify cefuroxime as "compatible" for use during pregnancy, stating that "human data indicate that cefuroxime (and other cephalosporins) not teratogenic at usual therapeutic doses" 1.

• The FDA drug label confirms reproduction studies in mice (up to 6.3 times human dose) and rabbits (2.1 times human dose) revealed no evidence of harm to the fetus 2
• A clinical follow-up study of 78 pregnant women treated with cefuroxime (13 in first trimester, 19 in second, 46 in third) found no abnormalities in physical or mental development of 80 infants followed for 18 months 3
• Recent 2026 pharmacokinetic data shows increased clearance during pregnancy, but evidence-based dosing regimens have been established for pregnant women 4

Clinical consideration: Standard dosing is appropriate, though awareness of increased drug clearance in late pregnancy may be relevant for severe infections.

N-Acetylcysteine (Mucolytic/Antioxidant)

N-acetylcysteine is safe during the third trimester based on animal reproduction data and clinical experience. The FDA label states that reproduction studies in rabbits at 2.6 times the human mucolytic dose showed no teratogenic effects 5.

• Animal studies (rats and rabbits) at doses up to 2.6 times human exposure demonstrated no impaired fertility or fetal harm 5
• Teratology studies in rabbits exposed to aerosolized N-acetylcysteine throughout organogenesis (days 6-18) showed no teratogenic effects 5
• Perinatal/postnatal rat studies with exposure from day 15 of gestation through 21 days postpartum showed no adverse effects on dams or newborns 5

Clinical consideration: While classified as "use only if clearly needed" due to lack of controlled human studies, the extensive animal safety data and clinical experience support its use when indicated.

Cetirizine (Second-Generation Antihistamine)

Cetirizine is safe and preferred for use during the third trimester 1, 6. Multiple guidelines specifically recommend cetirizine as a preferred antihistamine choice during pregnancy.

• The 2020 ERS/TSANZ guidelines state cetirizine is "probably safe" with the recommendation that "loratadine or cetirizine should be preferred as they have been most used" 1
• Cetirizine is classified as FDA Pregnancy Category B, indicating no evidence of fetal harm 6
• A meta-analysis including data from over 186,000 exposures in Scandinavian registries found no statistically significant associations with major congenital malformations, spontaneous abortions, or premature births 7
• A 2014 cohort study and meta-analysis confirmed cetirizine is not associated with increased teratogenic risk 8

Important caveat: One 2026 case report described fetal supraventricular tachycardia temporally associated with maternal cetirizine use combined with an antihistamine-decongestant in the third trimester 9. However, this single case involved combination therapy and does not outweigh the extensive safety data from large population studies.

The 2007 British guidelines note one older study associated antihistamine use in the last 2 weeks of pregnancy with retrolental fibroplasia in premature infants, though these findings were never corroborated 1.

Summary Recommendation

All three medications can be used safely in the third trimester when clinically indicated:

• Cefuroxime: Compatible throughout pregnancy with extensive human safety data
• N-acetylcysteine: Safe based on robust animal data and clinical experience
• Cetirizine: Preferred antihistamine with excellent safety profile from large population studies

The combination of these three medications has not been specifically studied together, but no pharmacological interactions or additive risks are expected based on their individual safety profiles and mechanisms of action.