What are the recommended antibiotics for acute mastitis in a lactating woman, including first‑line oral agents, alternatives for penicillin allergy, and options for MRSA risk or severe infection?

Recommended Antibiotics for Acute Mastitis in Lactating Women

For acute mastitis in breastfeeding women, dicloxacillin 500 mg orally four times daily or cephalexin 500 mg orally four times daily are the first-line antibiotics, with treatment duration of 10-14 days. 1, 2

First-Line Oral Antibiotics

Dicloxacillin is the oral agent of choice for methicillin-susceptible Staphylococcus aureus, which causes the majority of infectious mastitis cases. 1 The standard dose is 500 mg orally four times daily. 2 This antibiotic has minimal transfer into breast milk (relative infant dose of only 0.03%), making it extremely safe for the nursing infant. 3

Cephalexin is an equally effective alternative at 500 mg orally four times daily. 1, 2 Cephalosporins are generally considered safe during breastfeeding with minimal transfer to breast milk. 1, 4

Both antibiotics are effective against Staphylococcus aureus and are compatible with continued breastfeeding. 1, 2

Alternatives for Penicillin Allergy

For women with non-severe penicillin allergy (no history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours can be used if parenteral therapy is needed. 5
• Cephalexin remains an option as cross-reactivity is low. 1

For women with severe penicillin allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Erythromycin or azithromycin are acceptable alternatives, though there is a very low risk of infantile hypertrophic pyloric stenosis if macrolides are used during the first 13 days of the infant's life. 1, 6 After this period, they are generally considered safe. 1
• Clindamycin 300-450 mg orally three times daily is an option, but use with caution as it may increase gastrointestinal side effects in the infant, including diarrhea and candidiasis. 1, 6, 4

Options for MRSA Risk or Severe Infection

Consider MRSA coverage when:

• Local MRSA prevalence is high 1
• Patient has previous MRSA infection 1
• No response to first-line therapy within 48-72 hours 1
• Signs of systemic illness or sepsis 7

For suspected or confirmed MRSA:

• Clindamycin 600 mg IV every 8 hours or 300-450 mg orally three times daily. 5, 1 Monitor the infant closely for GI effects. 1, 6
• TMP-SMX (trimethoprim-sulfamethoxazole) 1-2 double-strength tablets twice daily orally. 5 Note that TMP-SMX lacks coverage for Streptococcus species, so consider adding a beta-lactam if streptococcal infection is possible. 5
• Linezolid 600 mg orally or IV twice daily. 5

For severe infection requiring hospitalization:

• Vancomycin 1 g IV every 12 hours. 5
• Linezolid 600 mg IV twice daily. 5
• Daptomycin 4 mg/kg IV once daily. 5

Treatment Duration and Monitoring

• Standard treatment duration is 10-14 days, though some sources suggest 7-10 days may be sufficient. 1, 2
• If symptoms do not improve within 48-72 hours of starting antibiotics, reevaluation is necessary to rule out abscess formation. 1
• Obtain milk cultures to guide antibiotic therapy, especially in immunocompromised patients or those with worsening/recurrent symptoms. 7
• Perform ultrasonography if abscess is suspected. 7

Critical Management Principles

Continued breastfeeding is essential and does not pose risk to the infant. 1, 2 In fact, regular breast emptying through continued breastfeeding helps resolve the condition. 1, 2

Conservative measures first: For early mastitis without systemic symptoms, a 1-2 day trial of NSAIDs, ice application, and feeding directly from the breast may be sufficient before starting antibiotics. 7 However, if symptoms persist beyond 12-24 hours, antibiotics should be added to prevent abscess formation, which occurs in approximately 10% of mastitis cases. 1, 2, 7

Common Pitfalls to Avoid

• Do not advise expressing and discarding breast milk. This is counterproductive and risks worsening mastitis through breast engorgement and blocked ducts. 1
• Avoid excessive pumping, heat application, and aggressive breast massage. These practices overstimulate milk production and cause tissue trauma, potentially worsening the condition. 7
• Do not use fluoroquinolones or tetracyclines as first-line agents in breastfeeding women due to potential infant developmental concerns. 6, 4
• Do not delay antibiotics beyond 48-72 hours if conservative measures fail, as this increases abscess risk. 1, 7