Primary pathogens (Staphylococcus aureus (MSSA > MRSA depending on local epidemiology) · Group A Streptococcus)
Clinical context (Localized breast erythema, pain, induration ± low-grade fever · no systemic toxicity · no drainable collection on exam/ultrasound)
First-line therapy
Cephalexin • p.o. • 25–25 mg/kg/dose • 3×/day
Max 1000 mg/dose · Max 3000 mg/day · Duration: 7 days · Typical 7 days; extend to 10 days if slow response or surrounding cellulitis
• MRSA coverage is not routine for mild non-purulent mastitis; add MRSA-active therapy when risk factors present (prior MRSA, household contact, high local prevalence, purulent focus/abscess, or beta-lactam failure) — IDSA SSTI principles, CPS.
• Reassess at 24–48 hours: progression, persistent fever, or new fluctuance warrants ultrasound, culture if drainage possible, and antibiotic adjustment.
• If abscess is present, antibiotics alone are often insufficient — arrange drainage (I&D or ultrasound-guided aspiration) plus culture-directed therapy.
Max 600 mg/dose · Max 1800 mg/day · Duration: 7 days · MRSA-active oral option when indicated; verify local susceptibility and consider D-test if inducible resistance concern
• MRSA risk factors: personal/household MRSA infection or colonization, recurrent abscesses, penetrating skin trauma, high local CA-MRSA prevalence, or prior beta-lactam failure at 48 h (IDSA SSTI, CPS).
• Non-anaphylactic beta-lactam allergy where cephalexin cannot be used (IDSA SSTI).
• Purulent drainage present and abscess cannot yet be excluded — obtain ultrasound and culture when possible.
Enter weight on Kids to calculate doses
Clinical notes
• Neonates vs older children: neonatal mastitis (≤28 days) more often bacteremic or associated with abscess; low threshold for admission, IV antibiotics, blood culture, and ultrasound (neonatal infection principles, AAP Red Book).
• Ultrasound: obtain when fluctuance is uncertain, symptoms fail to improve within 24–48 h, significant swelling, severe pain, or to evaluate for drainable abscess; ultrasound also guides aspiration/drainage (IDSA SSTI principles).
• Abscess/source control: breast abscess generally requires drainage (I&D or ultrasound-guided aspiration) plus culture — antibiotics alone have higher failure/recurrence.
• MRSA coverage: consider if purulent focus/abscess, prior MRSA, household MRSA, high local CA-MRSA rates, or failure of beta-lactam at 48 h; tailor to culture and local resistance (IDSA SSTI, CPS).
• Admission/IV criteria: systemic toxicity, inability to tolerate oral therapy, immunocompromise, failed outpatient therapy, rapidly progressive infection, suspected abscess requiring procedure, or any neonate/young infant with mastitis (NICE/IDSA SSTI principles; neonatal safety).
• IDSA — Practice guidelines for skin and soft tissue infections (purulent SSTI principles) (2014)
• CPS — Community-associated bacterial SSTI in children (2024)
• AAP Red Book — Staphylococcal and MRSA infections / neonatal infection principles (2024)
