Cephalexin Safety in Pregnancy
Yes, cephalexin is safe to use during pregnancy and is specifically recommended as a preferred β-lactam antibiotic for pregnant women based on decades of clinical experience showing no teratogenic effects.
Guideline-Based Safety Evidence
Cephalexin is explicitly identified as a preferred and safe antibiotic throughout all trimesters of pregnancy. 1, 2
Primary Safety Data
The American College of Obstetricians and Gynecologists recommends cephalexin as one of the safest first-line antibiotics for pregnant women, with decades of clinical experience demonstrating no teratogenic effects and compatibility throughout all trimesters and during breastfeeding. 2
The Infectious Diseases Society of America guidelines specifically state that β-lactam antimicrobials (usually ampicillin or cephalexin) are preferred because of their safety in pregnant women. 1
The American Academy of Dermatology provides moderate quality evidence supporting cephalexin use with no demonstrated harm to the fetus. 3
FDA Classification and Drug Label Information
FDA Pregnancy Category B: Reproduction studies in mice and rats using oral doses of cephalexin at 0.6 and 1.5 times the maximum daily human dose have revealed no harm to the fetus. 4
The FDA label notes that while animal studies show no fetal harm, there are no adequate and well-controlled studies in pregnant women, so the drug should be used during pregnancy only if clearly needed—this is standard Category B language and does not contraindicate use. 4
Clinical Applications During Pregnancy
Urinary Tract Infections
Cephalexin (500 mg every 6 hours orally) has been proven safe and effective for treating acute pyelonephritis in pregnancy, with a 91.4% success rate in nonbacteremic patients. 5
For recurrent UTI prophylaxis during pregnancy, postcoital cephalexin 250 mg as a single oral dose is highly effective, reducing UTI incidence from 130 infections pre-treatment to only 1 infection during 39 pregnancies. 6
Asymptomatic Bacteriuria
- For asymptomatic bacteriuria in pregnancy requiring 4-7 days of treatment, cephalexin is a preferred agent alongside nitrofurantoin. 1
Other Infections
- For hidradenitis suppurativa requiring systemic antibiotics during pregnancy, guidelines conditionally recommend cephalexin based on moderate quality evidence of safety. 3
Pharmacokinetic Considerations
Cephalexin crosses the placenta and reaches adequate levels in amniotic fluid and cord serum for inhibiting pathogens involved in materno-fetal infections. 7
Peak maternal serum concentrations occur approximately 1 hour after oral administration. 7
Comparative Safety Advantage
Cephalexin offers a significantly safer alternative to contraindicated antibiotics during pregnancy:
Avoid tetracyclines (doxycycline): cause tooth discoloration, transient bone growth suppression, and potential maternal fatty liver after the fifth week of pregnancy. 2
Avoid trimethoprim-sulfamethoxazole: especially in the first trimester due to increased risk of preterm birth, low birthweight, kernicterus, hyperbilirubinemia, and fetal hemolytic anemia. 2
Avoid fluoroquinolones: potential fetal cartilage damage. 2
Breastfeeding Compatibility
Cephalexin is excreted in breast milk, reaching a maximum level of 4 mcg/mL at 4 hours after a 500 mg dose, then disappearing by 8 hours. 4
Caution should be exercised when administering to nursing women, with monitoring of breastfed infants for gastrointestinal effects. 4, 2
Important Clinical Pitfalls
Drug interaction with metformin: Cephalexin can increase metformin plasma concentrations by 34% (Cmax) and 24% (AUC), requiring careful patient monitoring and dose adjustment of metformin. 4
Probenecid interaction: Renal excretion of cephalexin is inhibited by probenecid, as with other β-lactams. 4
Penicillin allergy: Cephalexin should be avoided in patients with a history of anaphylaxis, angioedema, respiratory distress, or urticaria to penicillins due to cross-reactivity risk. 2
False-positive glucose tests: Cephalexin can cause false-positive reactions for glucose in urine with Benedict's and Fehling's solutions and Clinitest® tablets. 4