Pharmacokinetics of nalidixic acid in man: hydroxylation and glucuronidation

Nalidixic acid is metabolized by hydroxylation to 7-hydroxymethylnalidixic acid[[ and then by oxidation to 7-carboxynalidixic acid.[[ The half-lives of the two elimination phases of nalidixic acid are 0.75 and 2.5 h. The apparent half-lives of the metabolite 7-hydroxymethylnalidixic acid are 2.5 and 5.5 h. Plasma protein binding of nalidixic acid is 95% and that of 7-hydroxymethylnalidixic acid 65%. The renal clearance of nalidixic acid varies between 2 and 25 ml/min and that of 7-hydroxymethylnalidixic acid between 37 and 162 ml/min. Of nalidixic acid 42% is glucuronidated and 40% hydroxylated. Of the hydroxy metabolite 57% is glucuronidated and 32% excreted unchanged. 7-Carboxynalidixic acid is excreted in the urine and is not glucuronidated. The variations in the glucuronidation/hydroxylation ratio of nalidixic acid and the glucuronidation/renal excretion ratio of the 7-hydroxymethyl metabolite belong to a normal distribution.