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Cefalexin

AEMPS

First-generation cephalosporin

ATC code: J01DB01

Updated · Methodology

Indications

A

Lactational mastitis

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.

Sources

  1. AEMPS: Ficha técnica de Cefalexina (2024)
  2. ABM: Academy of Breastfeeding Medicine Clinical Protocol #36: The Mastitis Spectrum (2022)

ICD-10: O91.2 · ICD-11: JB45.1

How to read tiers A–F
  • AStrong evidence – first or second line in international guidelines
  • BRecommended in selected cases
  • CStudy data contradict each other
  • DBenefit not proven, no documented harm
  • FDocumented harm, or risk without benefit

Mechanism of action

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%.

Safety

Contraindications

  • Anaphylaxis to cephalosporins or severe penicillin reaction
  • Severe renal impairment (dose adjustment)

Serious adverse effects

  • Pseudomembranous colitis (C. difficile)
  • Anaphylaxis
  • Stevens-Johnson syndrome (rare)

Common adverse effects

  • Diarrhea
  • Nausea
  • Skin rash
  • Candidiasis (thrush)
  • Headache

Pregnancy: can you take Cefalexin?

Safe in pregnancy. Not linked to birth defects.

Breastfeeding: can you take Cefalexin?

Hale L1 · Compatible

Fully compatible. Hale L1. RID about 0.5%, T½ 0.9 h. Peak in milk at 1 h. Possible infant thrush with prolonged use.

RID, infant dose via milk
0.5%
Maternal half-life
0.9 h
Maternal peak time
1 h
Peak milk concentration
0.5 mg/L
Milk-to-plasma ratio
0.01
Calculate RIDSafe feeding windowFull profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Practical notes

Timing and administration

Take 1 hour before or 2 hours after meals – food reduces bioavailability. May take with milk. Do not stop earlier than 10 days even with symptom relief.
Label mentions6 mentions

Verbatim lines from the interaction sections, in the language of the label

From this drug’s label

  • aminoglucósidosclass named in the label
    «Como con otros medicamentos betalactámicos, la excreción renal de cefalexina es inhibida por probenecid. La administración concomitante con otros principios activos, como aminoglucósidos, otras…»

    AEMPS, section 4.5 · Open on CIMA

  • antineoplásicosclass named in the label
    «Se ha descrito hipopotasemia en pacientes que toman fármacos citotóxicos para la leucemia cuando se les administró gentamicina y cefalexina.»

    AEMPS, section 4.5 · Open on CIMA

  • diuréticosclass named in the label
    «Como con otros medicamentos betalactámicos, la excreción renal de cefalexina es inhibida por probenecid. La administración concomitante con otros principios activos, como aminoglucósidos, otras…»

    AEMPS, section 4.5 · Open on CIMA

  • Furosemide
    «Como con otros medicamentos betalactámicos, la excreción renal de cefalexina es inhibida por probenecid. La administración concomitante con otros principios activos, como aminoglucósidos, otras…»

    AEMPS, section 4.5 · Open on CIMA

  • Gentamicin
    «Se ha descrito hipopotasemia en pacientes que toman fármacos citotóxicos para la leucemia cuando se les administró gentamicina y cefalexina.»

    AEMPS, section 4.5 · Open on CIMA

  • Metformin
    «En un estudio de 12 sujetos sanos a los que se les administraron dosis únicas de 500 mg de cefalexina y metformina, la C máx en plasma y el AUC de metformina aumentaron en un promedio del 34% y el…»

    AEMPS, section 4.5 · Open on CIMA

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Frequently asked

What is Cefalexin used for?

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.

What are the side effects of Cefalexin?

Common side effects of Cefalexin (≥ 1 in 100): Diarrhea, Nausea, Skin rash, Candidiasis (thrush), Headache. See the Safety section for uncommon and serious reactions.

Is Cefalexin safe during pregnancy?

Safe in pregnancy. Not linked to birth defects.

Is Cefalexin compatible with breastfeeding?

Fully compatible. Hale L1. RID about 0.5%, T½ 0.9 h. Peak in milk at 1 h. Possible infant thrush with prolonged use.

Who should not take Cefalexin?

Cefalexin is contraindicated in: Anaphylaxis to cephalosporins or severe penicillin reaction; Severe renal impairment (dose adjustment). Full list in the Safety section.

Official sources

Direct links to regulator labels. Open in a new tab.

Other drugs in this group

Cefditoren pivoxil, Ceftriaxone, Cefuroxime axetil, Chloramphenicol, Ciprofloxacin, Doxycycline, Levofloxacin, Norfloxacin