Is cephalexin (Keflex) safe to use during pregnancy?

Is Keflex (Cephalexin) Safe During Pregnancy?

Yes, cephalexin (Keflex) is safe to use during pregnancy and is considered a first-line antibiotic option for treating bacterial infections in pregnant women. 1

Safety Classification and Evidence

• Cephalexin is FDA Pregnancy Category B, meaning reproduction studies in animals at doses 0.6 to 1.5 times the maximum human dose have revealed no harm to the fetus 1
• The European Respiratory Society/Thoracic Society of Australia and New Zealand (ERS/TSANZ) classifies cephalexin and other cephalosporins as "Compatible" for use throughout all trimesters of pregnancy 2
• Human data indicate that cephalosporins, including cephalexin, are not teratogenic at usual therapeutic doses 2

Clinical Recommendations

Cephalexin can be used throughout pregnancy when clinically indicated for bacterial infections, with the following considerations:

When to Use Cephalexin

• First-line treatment option for susceptible bacterial infections during pregnancy, alongside penicillins 3, 4
• Particularly effective for urinary tract infections (UTIs), which are common in pregnancy 5
• Can be used for prophylaxis of recurrent UTIs during pregnancy at 250 mg postcoital dosing 5

Dosing and Monitoring

• Standard therapeutic doses are safe; no special dose adjustments required based on trimester 1
• The drug should be used during pregnancy "only if clearly needed," though decades of clinical experience support its safety 1, 4

Pharmacokinetics in Pregnancy

• Cephalexin crosses the placenta and reaches adequate levels in amniotic fluid and cord serum for antimicrobial activity 6
• Peak maternal serum concentrations occur approximately 1 hour after oral administration 6
• The drug is substantially excreted by the kidney 1

Use During Breastfeeding

• Cephalexin is compatible with breastfeeding 2
• The drug is excreted in human milk, reaching maximum levels of 4 mcg/mL at 4 hours post-dose, then disappearing by 8 hours 1
• Caution should be exercised, but no serious adverse effects in breastfed infants have been documented 1

Important Clinical Considerations

Advantages Over Other Antibiotics

• Safer than aminoglycosides (which carry nephrotoxicity and ototoxicity risks and should be avoided) 3
• Safer than tetracyclines (contraindicated after 5 weeks gestation due to tooth discoloration and bone effects) 2, 3
• Safer than fluoroquinolones (which should be avoided due to potential cartilage damage) 2, 3

When Antibiotics Are Necessary

• Untreated maternal infections pose greater risks to both mother and fetus than appropriate antibiotic therapy 3
• Infections during pregnancy can lead to abortion, preterm labor, premature rupture of membranes, and complications in the newborn 3
• The benefit of treating serious maternal infections outweighs theoretical antibiotic risks 4

Common Pitfalls to Avoid

• Do not withhold necessary antibiotic treatment due to pregnancy concerns when cephalexin is indicated 3
• Complete the full course of therapy as prescribed to prevent bacterial resistance 1
• Monitor for antibiotic-associated diarrhea, including potential Clostridioides difficile infection, even months after treatment 1

Drug Interactions in Pregnancy

• Metformin interaction: Cephalexin can increase metformin levels by 24-34% and decrease renal clearance by 14%; careful monitoring and dose adjustment of metformin is recommended if coadministered 1
• Probenecid: Inhibits renal excretion of cephalexin, potentially increasing drug levels 1