Safe Antibiotics for Bacterial Infections in Pregnant Women

First-Line Safe Antibiotics

The American College of Obstetricians and Gynecologists recommends penicillins, particularly amoxicillin, and cephalosporins, particularly cephalexin, as the safest first-line antibiotics for pregnant women with bacterial infections, with decades of clinical experience demonstrating no teratogenic effects and compatibility throughout all trimesters and during breastfeeding 1, 2
Amoxicillin is classified as Category A/B and is compatible throughout all trimesters and breastfeeding, with extensive human data showing no harm to the fetus at therapeutic doses 3, 2
Cephalexin has moderate-quality evidence supporting safety throughout pregnancy with no demonstrated fetal harm 1, 2

The American Academy of Pediatrics recommends avoiding tetracyclines, such as doxycycline, after the fifth week of pregnancy due to tooth discoloration, transient bone growth suppression, and potential maternal fatty liver of pregnancy 3, 2, 6
Trimethoprim-sulfamethoxazole should be avoided, especially during the first trimester, due to increased risk of preterm birth, low birthweight, kernicterus, hyperbilirubinemia, and fetal hemolytic anemia 3, 2, 6

For group B streptococcal infection, penicillin G is first-line: 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery 1
For chlamydia, erythromycin base 500 mg orally four times daily for 7 days or amoxicillin 500 mg orally three times daily for 7-10 days is recommended 1

Penicillins, such as amoxicillin, and cephalosporins are compatible with breastfeeding and considered low risk 6
Metronidazole is considered safe during breastfeeding; if single 2 g dose used, stop feeding for 12-24 hours 3, 6
Macrolides have very low risk of hypertrophic pyloric stenosis if used during first 13 days (safe after 2 weeks) 3, 6

All pregnant women should be screened for asymptomatic bacteriuria and Group B Streptococcus at 35-37 weeks gestation 1
Monitor all breastfed infants for gastrointestinal effects when mother receives antibiotics 6
Antibiotics in breast milk may cause falsely negative cultures if febrile infant requires evaluation 6