Nitrofurantoin Excretion in Human Milk

Six lactating white healthy women (26-36 years old, weighing 45-58 kg) were treated with 50 mg nitrofurantoin tablets, a urinary antiseptic. They received either 50 mg (group I; n = 3) or 100 mg (group II; n = 3) 3 times a day (09.00, 16.00, 19.00 h) for 24 h, 2-5 days after the delivery of a full-term neonate. The study was performed on the 4th dose at 09.00 h just before breakfast. Milk samples were collected before, 3 and 6 h after the nitrofurantoin administration with an Egnell SMB breast pump. The complete milk samples were collected from each breast, and pooled. 5 ml venous blood samples were drawn before, 1,2,3 and 6 h after nitrofurantoin administration. Plasma and milk nitrofurantoin concentrations were measured by HPLC. Apparent elimination half-life and apparent plasma clearance were the same in both groups, 0.8 ± 0.09 h and 27.6 ± 5.57 l/h, respectively. Nitrofurantoin was not detectable in the milk just before the 4th administration. The amount excreted in the milk within 6h after nitrofurantoin administration was 22-57 μg (I) and 61-284 μg (II) which represents 0.05-0.11 % (I) and 0.06-0.28 (II) of the nitrofurantoin dose. The nitrofurantoin concentration ratio of the breast milk to the plasma collected at 3 h was 2.2 ± 1.2 (I) and 2.3 ± 1.6 (II). These results show that nitrofurantoin excretion in human milk is low: below 0.12 (I) and 0.29% (II). It suggests that breast-fed newborn infants from mothers treated with nitrofurantoin would be exposed to small amounts of drug. Nevertheless, since in glucose-6-phosphate dehydrogenase-deficient individuals a very small amount of this drug may be sufficient to trigger a hemolytic reaction, nitrofurantoin should not be used by nursing mothers in populations with a high incidence of glucose-6-phosphate dehydrogenase deficiency.