How should acute lactational mastitis be managed in a breastfeeding woman presenting with a painful, swollen, erythematous breast and fever?

Management of Acute Lactational Mastitis

For a breastfeeding woman presenting with acute lactational mastitis (painful, swollen, erythematous breast with fever), initiate oral antibiotics targeting Staphylococcus aureus immediately—specifically dicloxacillin 500 mg four times daily or cephalexin 500 mg four times daily—while continuing breastfeeding from the affected breast. 1

Diagnostic Criteria

The diagnosis of lactational mastitis is primarily clinical and requires: 2, 3

• Rapid onset of unilateral breast erythema, edema, warmth, and focal tenderness 2
• Fever and systemic symptoms (malaise, flu-like symptoms) 3
• Onset typically within the first few months of breastfeeding 4
• No imaging required for straightforward cases; reserve ultrasound for patients not improving within 48-72 hours to exclude abscess 1, 5

First-Line Antibiotic Therapy

For Patients Without Penicillin Allergy

Dicloxacillin 500 mg orally four times daily for 7 days is the preferred first-line agent, targeting methicillin-susceptible S. aureus, the predominant pathogen. 1

Cephalexin 500 mg orally four times daily for 7 days is an equally effective alternative. 1

For Penicillin-Allergic Patients

Cephalexin 500 mg orally four times daily may be used in patients with non-immediate (non-IgE-mediated) penicillin hypersensitivity. 1

Clindamycin 300-450 mg orally three times daily is appropriate for true penicillin-allergic patients, though it may increase gastrointestinal side effects in the nursing infant. 1

Erythromycin or azithromycin are acceptable macrolide alternatives, but carry a very low risk of infantile hypertrophic pyloric stenosis if used during the first 13 days of the infant's life; they are generally safe after this period. 1

MRSA Coverage (When Indicated)

Consider MRSA-targeted therapy when: 1

• Local MRSA prevalence is high 1
• Previous MRSA infection in the patient 1
• No clinical response to first-line beta-lactam therapy within 48-72 hours 1

MRSA-Targeted Oral Regimens

Clindamycin 300-450 mg orally three times daily if the isolate is clindamycin-susceptible (resistance ranges 3-15%). 1

Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets orally twice daily provides MRSA coverage but lacks activity against Streptococcus species; add a concurrent beta-lactam if streptococcal infection is possible. 1, 6

Linezolid 600 mg orally twice daily is an alternative MRSA-active oral agent, though expensive and bacteriostatic. 1

Essential Supportive Measures

Continue breastfeeding from the affected breast—this does not pose risk to the infant and helps resolve the mastitis through regular breast emptying. 1, 3

Frequent, complete breast emptying reduces the risk of progression and abscess formation. 3

NSAIDs (ibuprofen or naproxen) for pain control and anti-inflammatory effect. 7

Warm or cold compresses applied to the affected breast for symptom relief. 7

Assess infant's latch and breastfeeding technique—poor attachment can precipitate mastitis through nipple trauma and incomplete emptying. 2, 3

Critical Pitfalls to Avoid

Never advise expressing and discarding breast milk—this is illogical and risks breast engorgement, blocked ducts, and worsening mastitis. 1

Do not delay antibiotic therapy when clinical signs of infection are present (fever, erythema, focal tenderness)—early treatment prevents abscess formation, which occurs in approximately 10% of mastitis cases. 1, 8, 3

Do not assume all cases are due to S. aureus—Streptococcus pyogenes can cause severe invasive mastitis with abscess formation and requires prompt recognition. 6

Indications for Urgent Reassessment

Reevaluate within 48-72 hours if: 1

• Symptoms worsen or fail to improve on appropriate antibiotics 1
• Development of a palpable mass or fluctuant area suggesting abscess 5
• Persistent fever beyond 48 hours of antibiotic therapy 3

Perform urgent ultrasound to identify abscess or mass if symptoms persist or worsen. 5

Breast abscess requires drainage—either needle aspiration or surgical drainage—in addition to antibiotics; breastfeeding can usually continue from the affected breast even with a treated abscess. 3, 5

Severe Cases Requiring Hospitalization

For severe mastitis with systemic toxicity requiring intravenous therapy: 1

Vancomycin 1 g IV every 12 hours is the parenteral drug of choice for MRSA or severe infection. 1

Cefazolin 2 g IV loading dose, then 1 g IV every 8 hours for penicillin-allergic patients without anaphylaxis risk. 1

Linezolid 600 mg IV twice daily or daptomycin 4 mg/kg IV once daily are alternative agents for severe cases. 1

Red Flags for Inflammatory Breast Cancer

Although rare, inflammatory breast cancer can mimic mastitis. Suspect malignancy when: 8

• Erythema occupies ≥1/3 of breast surface 8
• Peau d'orange present 8
• Symptoms persist beyond 1 week of appropriate antibiotics 8
• History of recurrent "mastitis" not responding to antibiotics in non-lactating women 8

If inflammatory breast cancer is suspected, obtain urgent ultrasound, diagnostic mammogram, punch biopsy of skin, and multidisciplinary oncology referral within 24-48 hours—delay significantly worsens mortality. 8