What antibiotics are safe for pregnant women?

Safe Antibiotics for Pregnant Women

Penicillins (such as amoxicillin) and cephalosporins (such as cephalexin) are the first-line antibiotics during pregnancy due to their established safety profiles and decades of clinical experience showing no harm to the fetus. 1, 2

First-Line Safe Antibiotics

Beta-Lactams (Preferred)

• Penicillins are the primary choice for most infections during pregnancy, including amoxicillin (500 mg orally three times daily) and penicillin V (500 mg orally twice daily), with reproduction studies showing no evidence of fetal harm at doses up to 3-6 times the human dose. 1, 3, 2
• Cephalosporins are equally safe first-line alternatives, particularly cephalexin, and should be prioritized for patients with non-anaphylactic penicillin allergies. 1, 3
• Cefazolin is specifically recommended for penicillin-allergic pregnant women requiring intravenous therapy (2 g IV initially, then 1 g IV every 8 hours). 1, 3

Macrolides (Safe with Caveats)

• Azithromycin is safe during pregnancy with no adverse effects reported in studies, making it suitable for chlamydial infections (1 g orally as a single dose). 1, 4
• Erythromycin base is safe and recommended for chlamydial infections in pregnancy (500 mg orally four times daily for 7 days), though gastrointestinal side effects may reduce compliance. 4, 1
• Erythromycin estolate is specifically contraindicated due to drug-related hepatotoxicity. 4

Other Safe Options

• Clindamycin has moderate safety evidence (300 mg orally four times daily for 10 days) and should be used for penicillin-allergic patients with anaphylaxis risk when susceptibility testing confirms sensitivity. 1, 3
• Metronidazole is permitted during pregnancy when indications are strictly verified, though it should be used as a second-line agent. 5, 6
• Nitrofurantoin is safe for uncomplicated urinary tract infections (avoid near term due to neonatal hyperbilirubinemia risk), with treatment duration of 7 days or at least 3 days after sterile urine. 4, 7

Infection-Specific Recommendations

Group B Streptococcal Prophylaxis

• Penicillin G: 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery. 1
• For penicillin allergy without anaphylaxis: Cefazolin 2 g IV, then 1 g IV every 8 hours. 1

Chlamydial Infections

• First-line: Erythromycin base 500 mg orally four times daily for 7 days OR amoxicillin 500 mg orally three times daily for 7-10 days. 4
• Alternative: Azithromycin 1 g orally as a single dose. 4, 1

Syphilis

• Penicillin is the only proven effective treatment for preventing maternal transmission and treating fetal infection, with the regimen matched to disease stage. 4
• Pregnant women with penicillin allergy must be desensitized and treated with penicillin, as no proven alternatives exist. 4

Antibiotics to Strictly Avoid

Absolutely Contraindicated

• Tetracyclines (including doxycycline) are contraindicated after the fifth week of pregnancy due to dental staining and potential bone growth inhibition in the fetus. 4, 1, 5
• Fluoroquinolones (ciprofloxacin, levofloxacin) should be avoided due to potential fetal toxicity affecting cartilage development. 1, 6

Use Only When Absolutely Necessary

• Aminoglycosides (gentamicin) should be avoided except for life-threatening gram-negative infections, with careful serum level monitoring required due to ototoxicity and nephrotoxicity risks. 1, 5, 8
• Trimethoprim-sulfamethoxazole should be avoided in the first trimester (birth defect risk) and near term (neonatal hyperbilirubinemia risk). 1, 6

Critical Clinical Considerations

Dosing Adjustments

• Pregnancy-induced physiologic changes (increased glomerular filtration rate, increased total body volume, enhanced cardiac output) may require dose adjustments for renally cleared antibiotics. 7
• Penicillin is occasionally prescribed at increased dosages (25.6% of cases), while erythromycin and amoxicillin are sometimes given at reduced dosages, though individualization based on pharmacokinetics is often needed. 9

Important Warnings

• Amoxicillin may reduce oral contraceptive efficacy by affecting intestinal flora and estrogen reabsorption. 2
• Treatment duration should typically be 7-10 days for most infections, with 10 days specifically required for streptococcal pharyngitis to prevent rheumatic fever. 3, 9
• All pregnant women should be screened for asymptomatic bacteriuria and Group B Streptococcus (at 35-37 weeks gestation). 1

Common Pitfall

The most critical error is withholding necessary antibiotic treatment due to pregnancy concerns—untreated infections pose far greater risks (preterm birth, low birth weight, spontaneous abortion) than appropriate antibiotic use with safe agents. 5, 7