What is the best antibiotic for treating mastitis?

Best Antibiotic for Mastitis

For treating mastitis in breastfeeding women, dicloxacillin or flucloxacillin is the first-line antibiotic of choice due to its effectiveness against Staphylococcus aureus, the most common causative organism, and its minimal transfer into breast milk.

Antibiotic Selection Algorithm

First-line options:

• Dicloxacillin: 500 mg orally four times daily for 5-7 days 1, 2
• Flucloxacillin/Cloxacillin: 500 mg orally four times daily for 5-7 days 3

Alternative options (for penicillin allergies):

• Cephalexin: 500 mg orally four times daily for 5-7 days 1
• Clindamycin: 300-450 mg orally three times daily for 5-7 days 4

For MRSA infections:

• Clindamycin: 300-450 mg orally three times daily 5
• Trimethoprim-sulfamethoxazole: 1-2 DS tablets orally twice daily 5

Rationale for Treatment Selection

Pathogen Considerations

Mastitis is most commonly caused by Staphylococcus aureus (S. aureus), which is frequently resistant to beta-lactamase sensitive antibiotics. Therefore, beta-lactamase resistant antibiotics like dicloxacillin or flucloxacillin are preferred 3.

Safety During Breastfeeding

Dicloxacillin/cloxacillin has minimal transfer into breast milk with a relative infant dose of only 0.03%, well below the theoretical level of concern of 10% 2. This makes it particularly suitable for breastfeeding mothers.

Treatment Approach

1. Effective milk removal is the most essential part of treatment and may make antibiotics unnecessary in some cases 3
2. Culture of milk should be obtained when possible to determine the infecting organism and its antibiotic sensitivity 3
3. Continue breastfeeding during treatment, as this helps with milk removal and generally does not pose a risk to the infant 1, 5

Special Considerations

MRSA Infections

As methicillin-resistant S. aureus (MRSA) becomes more common, it may become a more frequent cause of mastitis 1. In areas with high MRSA prevalence or for patients with previous MRSA infection, consider:

• Clindamycin (300-450 mg orally three times daily)
• Trimethoprim-sulfamethoxazole (1-2 DS tablets orally twice daily)
• Linezolid (600 mg orally twice daily) - though this should be reserved for severe cases due to its higher transfer into breast milk (15.61% relative infant dose) 6

Complications

Breast abscess is the most common complication of mastitis and can be prevented by early treatment and continued breastfeeding. If an abscess develops, surgical drainage or needle aspiration is needed, but breastfeeding can usually continue 1.

Important Clinical Pearls

• Regular feeding or expression of milk is an essential adjunct to antibiotic treatment 5
• Breastfeeding should continue on the affected side as long as the infant's mouth does not contact purulent drainage from the breast 5
• Approximately 10% of mastitis cases progress to breast abscesses, requiring drainage 5
• Most patients should show improvement within 48-72 hours of starting appropriate antibiotic therapy 4
• If no improvement is seen after 72 hours, consider reevaluation of diagnosis, changing antibiotic therapy, or possible drainage if abscess has formed 4

By following this evidence-based approach to antibiotic selection for mastitis, clinicians can effectively treat the infection while supporting continued breastfeeding and minimizing risks to both mother and infant.