Safe Antibiotics in First Trimester of Pregnancy

First-Line Safe Options

Penicillins (amoxicillin, ampicillin) are compatible throughout all trimesters with decades of clinical experience documenting safety, according to Praxis Medical Insights 1
First-generation cephalosporins (cephalexin) have moderate-quality evidence supporting safety throughout pregnancy with no demonstrated fetal harm, as stated by Praxis Medical Insights 1
Amoxicillin-clavulanate is compatible during the first trimester, though it should be avoided later if there's risk of preterm delivery due to potential necrotizing enterocolitis, as noted by Praxis Medical Insights 1

Azathioprine can be used at doses up to 2 mg/kg daily throughout pregnancy for specific rheumatologic conditions, according to the Annals of the Rheumatic Diseases 2
Methotrexate is proven teratogenic and must be discontinued 1-3 months before conception, as reported by the Annals of the Rheumatic Diseases 2 and 4

Tetracyclines (doxycycline) are strictly contraindicated after week 5 of pregnancy due to tooth discoloration, bone growth suppression, and potential maternal fatty liver, as stated by Praxis Medical Insights 1
Trimethoprim/Sulfonamides (co-trimoxazole) should be avoided during the first trimester due to neural tube defect risk and association with hyperbilirubinemia, according to Praxis Medical Insights 1 and 3
Aminoglycosides (gentamicin, tobramycin) are associated with eighth cranial nerve damage and nephrotoxicity, and should be reserved only for life-threatening infections, as noted by Praxis Medical Insights 3

Vancomycin has limited first-trimester experience and should only be used for life-threatening infections, as stated by Praxis Medical Insights 3
High-dose fluconazole (≥400 mg/day) during the first trimester is associated with craniosynostosis and dysmorphic facies, according to Praxis Medical Insights 3