Dicloxacillin is Safe During Breastfeeding
Dicloxacillin is safe to use during breastfeeding, with minimal transfer into breast milk and an extremely low relative infant dose of only 0.03% of the maternal dose. 1
Evidence Supporting Safety
Minimal Milk Transfer
- A 2020 pharmacokinetic study measured dicloxacillin levels in three breastfeeding mothers taking 500 mg every 6 hours for mastitis treatment 1
- The maximum concentration detected in breast milk was only 67.6 ng/mL, with a relative infant dose (RID) of 0.03%—well below the 10% threshold considered safe 1
- The minimal transfer is explained by dicloxacillin's high plasma protein binding (approximately 96%), which limits its penetration into breast milk 1
FDA and Clinical Guidance
- The FDA label states that "penicillins are excreted in breast milk" and recommends caution, but does not contraindicate breastfeeding 2
- Penicillins as a class have long been considered safe for breastfeeding mothers and infants, with extensive clinical experience supporting their use 1
- Most antibiotics in clinical use, including penicillinase-resistant penicillins like dicloxacillin, are considered suitable during breastfeeding 3
Clinical Considerations
Monitoring the Infant
- Monitor breastfed infants for gastrointestinal effects (diarrhea, candidiasis) due to potential alteration of intestinal flora 4
- Exercise caution in infants with known hypersensitivity to penicillins, though this is rare 1
- Be aware that antibiotics in breast milk could theoretically cause falsely negative cultures if the infant develops fever requiring evaluation 4
Practical Administration
- Dicloxacillin should be taken with at least 4 fluid ounces (120 mL) of water to minimize risk of esophageal irritation 2
- Avoid taking dicloxacillin in the supine position or immediately before bed 2
- Standard dosing (typically 500 mg every 6 hours) does not require adjustment for breastfeeding 1
Common Clinical Context
Dicloxacillin is frequently prescribed for lactational mastitis in breastfeeding women, making this a particularly relevant clinical scenario 1, 5. The drug effectively treats staphylococcal infections while allowing safe continuation of breastfeeding 1.