TY - JOUR T1 - Active Transport of Nitrofurantoin Across the Mammary Epithelium<em>In Vivo</em> JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 664 LP - 668 VL - 280 IS - 2 AU - Frank W. Kari AU - Robert Weaver AU - Margaret C. Neville Y1 - 1997/02/01 UR - http://jpet.aspetjournals.org/content/280/2/664.abstract N2 - Nitrofurantoin is a commonly used urinary tract antibiotic that has been found at high concentrations in human milk. In vivostudies in rats were carried out to determine the mechanism by which this drug crosses the mammary epithelium. Lactating rats were gavage-fed with nitrofurantoin, and their milk and plasma levels of the antibiotic were measured at intervals up to 8 hr. The average milk-to-plasma (M/P) ratio, calculated from the areas under the milk and plasma curves, respectively, was 23 compared with a ratio predicted to be about 0.3 on the basis of lipid partitioning and protein binding determinations. M/P ratios for two nitrofurantoin congeners were also calculated. The neutral compound furazolidone had a M/P ratio of about 1, as predicted, whereas the basic compound furaltadone had a M/P ratio of 3.49 compared with a predicted ratio of 1.4. These data suggest that nitrofurantoin and, to a lesser extent, furaltadone are actively transported across the mammary epithelium into milk. The American Society for Pharmacology and Experimental Therapeutics ER -