Transfer of methylprednisolone into breast milk in a mother with multiple sclerosis.

High-dose intravenous methylprednisolone, a glucocorticoid with powerful anti-inflammatory activities, has become increasingly important in treating acute relapses of multiple sclerosis (MS). This is a case report of a 36-year-old lactating female who was receiving a 3-day course of high-dose methylprednisolone (1000 mg IV) to treat MS. Breast milk samples were obtained at 1, 2, 4, 8, and 12 hours following a 2-hour intravenous infusion on days 1, 2, and 3. The relative infant dose was found to be 1.45%, 1.35%, and 1.15% for days 1, 2, and 3, respectively. Using the average measured concentrations (C(avg)) for days 1, 2, and 3, the estimated infant exposure was 0.207, 0.194, and 0.164 mg/kg/day, respectively, which is below the recommended dose given to neonates requiring methylprednisolone drug therapy. Infant exposure is low and mothers could continue to breastfeed if treatment with IV methylprednisolone is very brief. However, if the mother wishes to limit infant exposure further, she could wait 2 to 4 hours after IV methylprednisolone administration, thus significantly limiting the amount of drug in the breast milk.

Transfer of natalizumab into breast milk in a mother with multiple sclerosis.

Natalizumab (Tysabri) is a recombinant humanized antibody to α4-integrin that is approved by the Food and Drug Administration for the treatment of multiple sclerosis (MS) and Crohn disease. This is a case report of a 28-year-old woman with MS who was taking natalizumab (300 mg intravenously infused over 1 hour every 4 weeks) while breastfeeding her 11.5-month-old daughter 3 times a day. Breast milk samples were collected over a 50-day period after the patient's first drug infusion. The average concentration of natalizumab was 0.93 µg/mL/d, and the relative infant dose was 1.74% of the weight-adjusted maternal dose. Transfer of natalizumab into human milk increased over time and with subsequent injections, with the highest concentration of 2.83 µg/mL at day 50 with a relative infant dose of 5.3%. Because these data suggest continued accumulation of natalizumab in milk, and because we cannot provide an accurate assessment of levels of this drug at 24 weeks (steady state), we are unable to determine safety at this time.

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.