Active Transport of Nitrofurantoin into Human Milk

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Abstract
Study Objective. To determine the extent to which nitrofurantoin is transferred 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 nitrofurantoin 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 concentration 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, achieving concentrations in milk greatly exceeding those in serum. Concern is warranted for suckling infants younger than 1 month old, or for infants with a high frequency of glucose‐6–phosphate dehydrogenase deficiency or sensitivity to nitrofurantoin.