First-generation cephalosporin
ATC code: J01DB01 (Cefalexin)
Beta-lactam antibiotic. Blocks bacterial peptidoglycan cell wall synthesis via inhibition of transpeptidases (PBPs). Bactericidal against gram-positive cocci, especially Staphylococcus aureus (MSSA) and Streptococcus spp. Weak activity against gram-negatives. Oral bioavailability 90%.
First line
Lactational mastitis due to MSSA. Per ABM Protocol #36 2022 and SEGO 2023, first-line 500 mg 4 times daily for 10-14 days. If no improvement by 48 h – assess breast drainage, consider MRSA (switch to clindamycin) or abscess (ultrasound + aspiration). Continue breastfeeding on the affected side.
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Safe in pregnancy. Not linked to birth defects.
Fully compatible. Hale L1. RID about 0.5%, T½ 0.9 h. Peak in milk at 1 h. Possible infant thrush with prolonged use.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Cefalexin is evaluated for the following indications with varying evidence strength: Lactational mastitis (evidence tier A). See the full indication matrix with dosing and citations above on this page.
Common side effects of Cefalexin (≥ 1 in 100): Diarrhea, Nausea, Skin rash, Candidiasis (thrush), Headache. See the Safety section for uncommon and serious reactions.
FDA category B. Safe in pregnancy. Not linked to birth defects.
Fully compatible. Hale L1. RID about 0.5%, T½ 0.9 h. Peak in milk at 1 h. Possible infant thrush with prolonged use.
Cefalexin is contraindicated in: Anaphylaxis to cephalosporins or severe penicillin reaction; Severe renal impairment (dose adjustment). Full list in the Safety section.