Is Keflex (cephalexin) effective for treating mastitis?

Keflex (Cephalexin) for Mastitis

Cephalexin is an appropriate first-line antibiotic for lactational mastitis when methicillin-susceptible Staphylococcus aureus (MSSA) is suspected, but it should NOT be used if methicillin-resistant S. aureus (MRSA) is a concern. 1

Primary Treatment Approach

When Cephalexin is Appropriate

• Cephalexin is effective against S. aureus, the most common causative organism in lactational mastitis 1
• The typical dosing is 500 mg orally every 6 hours 2
• Cephalexin should be combined with optimized breastfeeding technique and frequent, complete breast emptying 1
• Continued breastfeeding should be strongly encouraged during treatment and does not pose risk to the infant 1

Critical Limitation: MRSA Consideration

• As MRSA becomes increasingly common, cephalexin may fail as empiric therapy since it has NO activity against MRSA 3, 1
• Cephalexin only appears in MSSA treatment categories in IDSA guidelines and should never be used for confirmed or suspected MRSA infections 3
• If the patient fails to improve within 48-72 hours on cephalexin, MRSA should be suspected and therapy changed 3

Algorithm for Antibiotic Selection in Mastitis

Step 1: Assess Risk Factors for MRSA

• If MRSA risk factors present (prior MRSA infection, healthcare exposure, failed initial therapy, severe/rapidly progressive infection), do NOT use cephalexin 3
• Instead, use trimethoprim-sulfamethoxazole (1-2 double-strength tablets twice daily) or clindamycin (300-450 mg four times daily) 3

Step 2: Initial Empiric Therapy for Low MRSA Risk

• Cephalexin 500 mg every 6 hours OR dicloxacillin are appropriate first-line agents 1, 2
• Obtain cultures when possible before starting antibiotics 3

Step 3: Reassessment at 48-72 Hours

• If no improvement by 48-72 hours, switch to anti-MRSA coverage 3
• Adjust therapy based on culture results if available 3

Adjunctive Measures (Essential for Success)

• Work with a lactation consultant to optimize breastfeeding technique and latch 1
• Ensure frequent, complete breast emptying to reduce mastitis risk 1
• Address sore nipples, which can precipitate mastitis (evaluate for poor latch, infant mouth anomalies, or infection) 1
• Use pain medication as needed 4

Common Pitfalls to Avoid

• Do not assume all staphylococcal infections are methicillin-susceptible without obtaining cultures 3
• Do not continue cephalexin if the patient fails to improve within 48-72 hours—this suggests MRSA or abscess formation 3, 1
• Do not discontinue breastfeeding during mastitis treatment, as this worsens milk stasis and increases abscess risk 1
• Watch for breast abscess development (the most common complication), which requires surgical drainage or needle aspiration in addition to antibiotics 1

Evidence Quality Note

The Cochrane review found insufficient high-quality evidence to definitively confirm antibiotic effectiveness for mastitis, though clinical practice strongly supports their use 4. The evidence base comparing specific antibiotics is particularly weak, with only small trials available 4. However, given the clinical severity of untreated mastitis and risk of abscess formation, antibiotic therapy targeting S. aureus remains standard practice 1.