Nalidixic acid kinetics after single and repeated oral doses

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Abstract
Nalidixic acid, 1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naphtyridine-3-carboxylic acid (NA), is an antibacterial widely used for urinary tract infections. The kinetics of NA and its 2 metabolites, 7-hydroxynalidixic acid (HNA) and 7-carboxynalidixic acid (CNA), were studied after a single oral dose and after 2 doses a day for 7 days. Total unconjugated NA, HNA and CNA concentrations in plasma and urine samples were assayed by a new high-pressure liquid chromatographic technique. NA was rapidly absorbed and hydroxylated to HNA. Both were rapidly excreted in urine with an apparent elimination half-life of 6-7 h. CNA was never detected in the plasma, but it accounted for .apprx. 25% of total urinary NA and metabolites. No major sex-related differences in the kinetics and the metabolic pattern were observed. During the 7 day treatment there was no significant cumulation of NA and HNA. The concentration of the active compounds, unconjugated NA and HNA, was > 5 times the minimum bacteria inhibiting concentration for 8 h after drug and slightly above this concentration during the next 4 h.

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