What antibiotics are safe for pregnant women with bacterial infections?

Safe Antibiotics for Bacterial Infections in Pregnant Women

Penicillins (particularly amoxicillin) and cephalosporins (particularly cephalexin) are 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

First-Line Safe Antibiotics

Beta-Lactams (Preferred)

• 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, 4
• Cephalexin has moderate-quality evidence supporting safety throughout pregnancy with no demonstrated fetal harm 1, 2
• Amoxicillin-clavulanate is compatible during pregnancy but should be avoided in women at risk of preterm delivery due to a very low risk of necrotizing enterocolitis 2
• Ceftriaxone provides reliable coverage for gram-positive, gram-negative, and anaerobic bacteria and is recommended as an alternative to conventional peripartum regimens 3
• Piperacillin-tazobactam is explicitly listed as "compatible" for use during pre-conception and first trimester, with all penicillins considered low risk 3, 2

Macrolides (Safe Alternatives)

• Azithromycin is safe for use in pregnancy with no adverse effects reported in studies of pregnant patients 1
• Erythromycin (except erythromycin estolate) is probably safe during pregnancy, though one epidemiological study suggested a small increase in risk of cardiovascular defects and pyloric stenosis 3
• Erythromycin base 500 mg orally four times daily for 7 days is recommended for chlamydial infections in pregnant women 3, 2

Other Safe Options

• Clindamycin has moderate evidence supporting its safety in pregnancy with no significant risks of congenital anomalies or preterm delivery 1, 2
• Metronidazole can be used during pregnancy if there are no safer alternatives, though it is associated with fetal damage in animals (no confirmed reports in humans) 3, 5
• Nitrofurantoin is generally considered safe and effective in pregnancy for uncomplicated urinary tract infections 5, 6
• Fosfomycin is considered safe and effective in pregnancy 5, 6

Antibiotics to STRICTLY AVOID

Tetracyclines (Contraindicated)

• Doxycycline and all tetracyclines are contraindicated after the fifth week of pregnancy due to tooth discoloration, transient bone growth suppression, and potential maternal fatty liver of pregnancy 3, 2, 7
• Tetracyclines should be avoided during second and third trimesters and at delivery 3

Trimethoprim-Sulfamethoxazole (Avoid, Especially First Trimester)

• Trimethoprim 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, 7
• Co-trimoxazole should be avoided during the first trimester due to neural tube defect risk; if necessary, supplement with 5 mg/day folic acid 2

Aminoglycosides (Avoid If Possible)

• Aminoglycosides (gentamicin, tobramycin) should be avoided if possible due to eighth cranial nerve toxicity (ototoxicity) and theoretical nephrotoxicity in the fetus 3, 7
• If aminoglycosides must be used for life-threatening infections, monitor levels carefully, use once-daily dosing, and perform renal function and auditory testing in the neonate if treatment is prolonged 3

Fluoroquinolones (Contraindicated)

• Fluoroquinolones are contraindicated during pregnancy as a precautionary measure due to concerns about cartilage damage in animal studies 8, 5

Infection-Specific Recommendations

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 penicillin allergy without anaphylaxis risk: cefazolin 2 g IV initially, then 1 g IV every 8 hours 1
• For penicillin allergy with anaphylaxis risk: clindamycin or vancomycin if susceptibility confirmed 1

Urinary Tract Infections

• For asymptomatic bacteriuria: single-dose antimicrobial to which organism is susceptible 9
• For symptomatic UTI: amoxicillin 500 mg three times daily for 3 days 9
• Nitrofurantoin and fosfomycin are safe alternatives for uncomplicated UTI 5, 6

Sexually Transmitted Infections

• 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 1
• Azithromycin 1 g orally as single dose may be considered as alternative for chlamydia 1

Critical Trimester-Specific Considerations

First Trimester (Highest Risk Period)

• Avoid trimethoprim-sulfamethoxazole due to neural tube defect risk 2, 7
• Avoid sulfonamides due to association with hyperbilirubinemia 2
• Tetracyclines are strictly contraindicated after week 5 2

Second and Third Trimesters

• Continue avoiding tetracyclines due to tooth discoloration and bone growth suppression 3, 2
• Avoid sulfonamides near term due to risk of neonatal hyperbilirubinemia 1

At Delivery

• Avoid tetracyclines and sulfonamides 3
• If rifampin used long-term, give vitamin K to mother and neonate to prevent bleeding 3

Breastfeeding Considerations

Safe During Breastfeeding

• Penicillins (amoxicillin, ampicillin) are compatible with breastfeeding and considered low risk 7
• Cephalosporins are compatible with breastfeeding and have low oral bioavailability in infants 7
• Metronidazole is considered safe during breastfeeding; if single 2 g dose used, stop feeding for 12-24 hours 3, 7

Use with Caution During Breastfeeding

• Macrolides have very low risk of hypertrophic pyloric stenosis if used during first 13 days (safe after 2 weeks) 3, 7
• Clindamycin may increase risk of gastrointestinal side effects in infant 7
• Aminoglycosides: avoid breastfeeding for 2 hours following IV injection when concentration is maximal 3, 7

Avoid During Breastfeeding

• Fluoroquinolones should not be used as first-line due to theoretical cartilage damage concerns (ciprofloxacin preferred if class necessary) 7
• Doxycycline should be limited to maximum 3 weeks without repeating courses 7

Important Clinical Pitfalls

• All pregnant women should be screened for asymptomatic bacteriuria and Group B Streptococcus at 35-37 weeks gestation 1
• Prophylactic antibiotics should not be used before the intrapartum period to treat GBS colonization 1
• Physiologic changes in pregnancy (increased GFR, total body volume, cardiac output) may require dose adjustment or careful monitoring 5
• Monitor all breastfed infants for gastrointestinal effects when mother receives antibiotics 7
• Antibiotics in breast milk may cause falsely negative cultures if febrile infant requires evaluation 7
• Repeat urine cultures 7 days following therapy to assess cure or failure 9