Active transport of nitrofurantoin into human milk

Study Objective. To determine the extent to which nitrofurantoin is transfe rred into human milk. Design. Prospective, single-dose pharmacokinetic study Setting. University-affiliated clinical research center. Patients. Four healthy lactating women 8-26 weeks postpartum. Intervention. All subjects received a single, oral, 100-mg dose of nitrofur antoin macrocrystals with food. Serial serum and milk samples were obtained and analyzed by high-performance liquid chromatography Measurements and Main Results. Milk pH, milk fat partitioning, and protein binding in serum and milk were determined. Predicted milk:serum ratio (M:S) was compared with the observed M:S. Nitrofurantoin M:S predicted was 0.28 +/- 0.05, whereas M:S observed was 6.21 +/- 2.71. Average milk concentratio n was 1.3 mg/L, and estimated suckling infant dosage was 0.2 mg/kg/day or 6 % of maternal dose (mg/kg). Conclusions. Nitrofurantoin is actively transported into human milk, achiev ing concentrations in milk greatly exceeding those in serum. Concern is war ranted for suckling infants younger than I month old, or for infants with a high frequency of glucose-6-phosphate dehydrogenase deficiency or sensitiv ity to nitrofurantoin.