Transfer of linezolid into breast milk

Linezolid, a broad-spectrum antibiotic used primarily for treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections, is the first oxazolidinone approved for clinical use. This is a case report of a 30-year-old woman who was exclusively breastfeeding her infant prior to taking linezolid 600 mg orally every 12 hours to treat a MRSA mastitis. Breast milk samples were obtained over a 12-hour dosing interval on day 1 (after a single dose of therapy) and again on day 14 (at steady state). The relative infant dose at steady state was found to be 15.61% on day 14 of therapy. Using the average concentration at steady state, the estimated infant dose would have been 1.84 mg/kg/day, which is well below the recommended dose given to neonates requiring linezolid drug therapy. The infant did not breastfeed during maternal treatment with linezolid.