What is the appropriate management of right‑breast mastitis in a lactating woman, including antibiotic choice, continuation of breastfeeding or milk expression, and indications for imaging or abscess drainage?

Management of Right Breast Mastitis in a Lactating Woman

Initial Conservative Management (First 12–24 Hours)

Begin with a 1–2 day trial of conservative measures before adding antibiotics: NSAIDs for pain, ice application, and continued direct breastfeeding from the affected right breast. 1

• Most mastitis cases are inflammatory rather than infectious, with 14–20% resolving spontaneously within this timeframe. 1
• Continue breastfeeding directly from the right breast—this is essential for clinical resolution and does not endanger the infant. 1
• Avoid expressing and discarding milk, as interrupting breastfeeding causes engorgement, blocked ducts, and worsening mastitis. 1
• Do not recommend excessive pumping, heat application, or aggressive breast massage, as these practices exacerbate inflammation and tissue injury. 1

When to Add Antibiotics

If symptoms do not improve within 12–24 hours of conservative management, initiate narrow-spectrum antibiotics immediately. 1

• Delaying antibiotic therapy beyond 24 hours increases the risk of abscess formation, which occurs in approximately 10% of mastitis cases. 1, 2, 3

First-Line Antibiotic Selection

Dicloxacillin 500 mg orally four times daily for 10–14 days is the preferred first-line agent for methicillin-susceptible Staphylococcus aureus, which causes the majority of infectious mastitis. 1, 2

Alternative First-Line Options:

• Cephalexin 500 mg orally four times daily is equally effective and particularly useful for patients with non-severe penicillin allergy. 1, 2
• Both dicloxacillin and cephalexin are safe during breastfeeding with minimal transfer to breast milk. 1, 4

For True Penicillin Allergy:

• Clindamycin 300–450 mg orally three times daily is appropriate for patients with immediate hypersensitivity to penicillin, though it may increase gastrointestinal side effects in the infant. 2

MRSA Coverage (When Indicated)

Consider MRSA-targeted therapy if there is high local MRSA prevalence, previous MRSA infection, or failure to respond to first-line beta-lactam antibiotics within 48–72 hours. 1, 2

MRSA-Targeted Oral Regimens:

• Clindamycin 300–450 mg orally three times daily if the isolate is clindamycin-susceptible (resistance ranges 3–15%). 2
• 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. 2
• Avoid TMP-SMX in infants ≤28 days old or those with jaundice, prematurity, or G6PD deficiency due to risk of bilirubin displacement and hemolytic anemia. 1
• Linezolid 600 mg orally twice daily is an alternative MRSA-active agent, though expensive. 2

Continuation of Breastfeeding During Treatment

The patient should continue breastfeeding directly from the right breast throughout antibiotic therapy—this aids recovery and is safe for the infant. 1, 2, 3

• Breastfeeding may be maintained on the involved side provided the infant's mouth does not contact purulent drainage. 1
• All recommended antibiotics (dicloxacillin, cephalexin, clindamycin, amoxicillin/clavulanic acid, macrolides) are compatible with breastfeeding. 1, 2

Indications for Imaging

Obtain ultrasound imaging if symptoms persist 48–72 hours despite appropriate antibiotics, or if the patient lacks fever or systemic signs. 1

• For women ≥30 years old: mammography with ultrasound. 1
• For women <30 years old: ultrasound alone. 1
• Urgent ultrasound within 48 hours is warranted if erythema occupies at least one-third of the breast surface or peau d'orange appearance is present. 1

Indications for Abscess Drainage

Breast abscess occurs in approximately 10% of mastitis cases and requires surgical drainage or needle aspiration. 1, 2, 3

• Suspect abscess if a fluctuant mass is palpable or ultrasound demonstrates a fluid collection. 3
• Breastfeeding can usually continue from the affected breast even after abscess drainage. 3

Criteria for Hospital Admission

Admit patients with systemic symptoms suggesting sepsis risk, such as fever with chills, tachycardia, tachypnea, or abnormal white blood cell count. 1, 2

Intravenous Therapy for Severe Cases:

• Vancomycin 1 g IV every 12 hours for MRSA or severe infection. 2
• Cefazolin 2 g IV loading dose, then 1 g IV every 8 hours for non-severe penicillin allergy. 2
• Linezolid 600 mg IV twice daily or daptomycin 4 mg/kg IV once daily are alternatives. 2

Red Flags Requiring Urgent Evaluation

Symptoms persisting beyond 1 week of appropriate antibiotics may indicate inflammatory breast cancer and warrant urgent evaluation. 1

• The probability that focal breast pain represents underlying malignancy ranges from 1.2% to 6.7%, though breast cancer rarely presents with pain alone. 1

Common Pitfalls to Avoid

• Never advise expressing and discarding breast milk—this interrupts nursing and worsens mastitis. 1
• Avoid recommending excessive pumping, heat, or aggressive massage—these exacerbate inflammation. 1, 5
• Do not delay antibiotics beyond 24 hours if conservative measures fail—this increases abscess risk. 1
• Ensure a breast pump is available if prolonged separation occurs, to reduce mastitis risk. 6