What is the recommended first-line antibiotic regimen for acute lactational mastitis in an otherwise healthy postpartum woman?

First-Line Antibiotic for Acute Lactational Mastitis

For acute lactational mastitis in an otherwise healthy postpartum woman, dicloxacillin 500 mg orally four times daily or cephalexin 500 mg orally four times daily are the recommended first-line antibiotics, targeting methicillin-susceptible Staphylococcus aureus, which causes the majority of infectious mastitis cases. 1

Initial Conservative Management (Before Antibiotics)

• Start with a 1-2 day trial of conservative measures including NSAIDs, ice application, feeding the infant directly from the breast, and minimizing pumping, as most cases of mastitis are caused by inflammation rather than true infection. 2
• If symptoms do not improve within 12-24 hours of conservative management, add antibiotics to prevent abscess formation, which occurs in approximately 10% of mastitis cases. 1, 3

First-Line Antibiotic Regimens

• Dicloxacillin 500 mg orally four times daily is the oral agent of choice for methicillin-susceptible S. aureus, which causes the majority of infectious mastitis. 1
• Cephalexin 500 mg orally four times daily is an equally effective alternative, particularly useful for patients with non-severe penicillin allergies. 1
• Both antibiotics are classified as "compatible" with breastfeeding and are safe for the nursing infant. 4, 1

Alternative Regimens for Penicillin Allergy

• Amoxicillin/clavulanic acid is a broad-spectrum alternative that is safe during breastfeeding, classified as FDA Category B and explicitly "compatible" with nursing. 4, 1
• Erythromycin or azithromycin are acceptable alternatives for penicillin-allergic patients, though there is a very low risk of infantile hypertrophic pyloric stenosis if macrolides are used during the first 13 days of infant life. 1
• Clindamycin is an option for suspected or confirmed MRSA, but use with caution as it may increase GI side effects in the infant, including diarrhea, candidiasis, or rarely antibiotic-associated colitis. 4, 1

When to Consider MRSA Coverage

• Consider MRSA coverage if local MRSA prevalence is high, the patient has a previous MRSA infection, or there is no response to first-line therapy within 48-72 hours. 1
• For suspected MRSA, clindamycin is the preferred oral agent, though infant monitoring for GI effects is essential. 1

Critical Management Points

• Continue breastfeeding during antibiotic treatment—this does not pose a risk to the infant and actually helps resolve the mastitis by ensuring regular breast emptying. 1, 3
• Dicloxacillin transfers into breast milk at very low levels (relative infant dose 0.03%), well below the 10% threshold of concern. 5
• Reassess within 48-72 hours—if symptoms worsen or do not improve, reevaluate to rule out breast abscess, which requires surgical drainage or needle aspiration. 1, 3

Common Pitfalls to Avoid

• Do not advise expressing and discarding breast milk—this is illogical and risks breast engorgement, blocked ducts, and worsening mastitis. 1
• Avoid excessive pumping, heat application, and aggressive breast massage—these practices overstimulate milk production and cause tissue trauma, potentially worsening the condition. 2
• Do not delay antibiotics beyond 24 hours if conservative measures fail, as this increases the risk of abscess formation. 1

Infant Monitoring

• Monitor breastfed infants for gastrointestinal effects (diarrhea, gastroenteritis) due to alteration of intestinal flora from maternal antibiotic use. 4
• All recommended antibiotics (dicloxacillin, cephalexin, amoxicillin/clavulanic acid) are considered compatible with breastfeeding, with minimal transfer to breast milk. 4, 1