Excretion of nalidixic acid via mother's milk

Following the oral administration of 2.0 g nalidixic acid (NA) to lactating women only 0.003% of the dose was excreted chemotherapeutically active in the total 24 h milk. In milk, minimal inhibitory concentrations of nalidixic acid were never reached. 6-8 h after medication the milk/serum quotient was 0.061 +/- 0.003.