Mastitis Organism-Specific Therapy

Organism-specific regimens for mastitis are provided below, including those for Staphylococcus aureus, coagulase-negative staphylococci, staphylococci, streptococci, and Peptostreptococcus.

Mastitis most commonly is caused by S Aureus. ^[1]

Methicillin-sensitive S aureus or coagulase-negative staphylococci

Treatment Duration 10-14 days ^{[2, 3]}

Routine cases without risk factors for MRSA:

• Amoxicillin-clavulanate 875 mg/125 mg PO BID  ^[4]
• Cephalexin 500 mg PO QID  
• Dicloxacillin 500 mg PO QID

If penicillin intolerance (not allergy):

• Cephalexin 500 mg PO QID 

​If beta-lactam allergy:

• Clindamycin 450 PO TID (questionable safety if breastfeeding)

When clinical improvement is apparent, transition the patient from IV to oral antibiotics for completion of a 10- to 14-day course. ^{[5, 6, 7, 8, 9]}

Methicillin-resistant S aureus or coagulase-negative staphylococci

Treatment Duration 10-14 days

Initial or routine cases:

• Clindamycin 600 mg IV q8h infuse over 10-60 minutes (max 30 mg/min) or 300 mg PO TID  (First Line)  ^{[2, 9]}
• Trimethoprim-sulfamethoxazole 160 mg/800 mg 1 DS tablet BID ( Caution in women breastfeeding infants under 2 months old or immunocompromised infants   ^[5] )

For severe Infections: 

• Vancomycin 1 g IV q12h, target trough levels of 10-15 mcg/mL (MSSA) or 15-20 mcg/mL (MRSA); infusion not to exceed 1 g/hour

For rare strains or refractory cases:

• L inezolid 600 mg PO/IV q12h for 10-14 days, infuse over 30-120 minutes (pregnancy category C; secreted in breast milk, caution if used while breastfeeding) 
• T igecycline 100-mg IV infusion, then 50-mg IV infusion q12h for 5-14 days; infuse over 30-60 minutes​ (pregnancy Category D, suspected to be secreted in breast milk; do not use in pregnancy or if breastfeeding) 
• Daptomycin 4 mg/kg IV infusion q24h for 7-14 days; infuse over 30 minutes (pregnancy category B; secreted in breast milk in low concentrations, although it has poor oral bioavailability; use caution if breastfeeding)

Streptococci or peptostreptococci

Routine:

• Amoxicillin-clavulanate 875 mg/125 mg PO BID for 10-14 days or
• Cephalexin 500 mg PO QID for 10-14 days or
• Clindamycin 600 mg IV q8h infuse over 10-60 minutes (max 30 mg/min) or 300 mg PO TID for 10-14 days or
• Dicloxacillin 500 mg QID for 10-14 days or
• Flucloxacillin 250-500 mg QID for 5-7 days ^[4] or
• Nafcillin 2 g IV q4h for 10-14 days; infuse over 30-60 minutes or
• Oxacillin 2 g IV q4h for 10-14 days; infuse over 30 minutes

​Emerging treatment options

The following drugs have been approved by the FDA for treatment of soft-tissue infections but have not yet been assessed specifically for efficacy in treating breast infections.

• Ceftaroline 600 mg IV q12h; infuse over 5-60 minutes for 5-14 days (approved to treat MRSA infections; pregnancy Category B, unknown if secreted in breast milk) or
• Dalbavancin: (1) 1-dose regimen of 1500 mg IV or (2) 2-dose regimen of 1000 mg IV followed 1 week later by 500 mg IV; infuse IV over 30 minutes (pregnancy category C, unknown if secreted in breast milk) or
• Oritavancin: 1-dose regimen of 1200 mg dose IV infusion over 3 hours. (pregnancy category C, unknown if secreted in breast milk) or
• Delafloxacin 450 mg PO q12h for 10-14 days or 300 mg IV q12h for 10-14 days; infuse over 60 minutes (no pregnancy classification, unknown if secreted in breast milk, use caution if pregnant or breastfeeding ) ^{[10, 11]}

When clinical improvement is apparent using ceftaroline, transition the patient from IV to oral antibiotics for completion of a 10- to 14-day course. ^{[5, 6, 7, 12, 13]} When using dalbavancin or oritavancin, additional antibiotics are not required except as indicated for failure of clinical resolution.

Fungal mastitis

Fungal mastitis should be suspected when pain is disproportional to clinical findings. Pain is often described as “shooting from nipple through the breast to the chest wall.” ^[14]   A "burning" sansation, rather than pain has also been reported. ^[5]  Concurrent yeast infections, such as oral thrush or diaper dermatitis, are common. The infant should be treated, as well as the mother. ^[5]  Evidence regarding treatment is conflicting. ^[11]

Mild infections: (treatment Duration 2 weeks) ^[5]

• Nystatin topical applied to affected area q8-12hr (pregnancy category B, no lactation information) 
• Miconazole topical applied to affected area BID (pregnancy category C, no lactation information)
• Ketoconazole topical applied to affected area once daily (pregnancy category C, no lactation information)

Moderate-to-severe infections:

• Fluconazole 400 mg IV/PO (initial dose), followed by 200 mg daily, for a minimum of 10 days. Single large doses are ineffective. Infants are not adequately treated with the amount of fluconazole that is passed via breast milk and therefore should be treated independently with 6-12 mg/kg initial dose, followed by 3-6 mg/kg/day for a minimum of 10 days. ^[5]

Recurrent mastitis

Consider the following:

• Rule out abscess with ultrasonography.
• Consider choosing an antibiotic to cover (MRSA). ^[5]
• If an abscess develops, consider irrigation and debridement along with IV antibiotics.

Special considerations

If lactating:

• Milk culture is not specific; 1 mL of normal breast milk may contain >1000 colonies of skin flora
• Milk stasis (as with skipped or incomplete feedings) is a major risk factor for mastitis