1-ethyl-7-methyl-4-oxo-[1,8]naphthyridine-3-carboxylic acid

Absorption
Nalidixic acid is rapidly absorbed from the GI tract. C max is 20 to 40 mcg/mL and T max is 1 to 2 hr.

Distribution
Nalidixic acid concentrates in urine and seminal fluid; protein binding is 90%.

Metabolism
Partially metabolized in liver to hydroxynalidixic acid (activity similar to nalidixic acid) and inactive conjugates. Hydroxynalidixic acid represents 30% of the biologically active drug in the blood and 85% in the urine.

Elimination
Rapidly excreted through the kidney with a t ½ of about 90 min. Approximately 4% excreted in the feces. Peak levels of active drug average approximately 150 to 200 mcg/mL 3 to 4 hr after administration, with a t ½ of about 6 hr.

Special Populations
Renal Function Impairment
Expected to decrease Cl, increase serum concentrations, and decrease urine levels of parent and active metabolite.

Antacids (containing aluminum, calcium, or magnesium), sucralfate, divalent or trivalent cations (eg, iron), multivitamins (containing zinc), buffered tablets (eg, didanosine)
May interfere with quinolone absorption; do not take within 2 hr before or after nalidixic acid.

Anticancer agents (eg, melphalan)
Increased risk of serious GI toxicity.

Anticoagulants (eg, warfarin)
May enhance anticoagulant effects.

Bacteriostatic agents (eg, chloramphenicol, nitrofurantoin, tetracycline)
May inhibit the action of nalidixic acid.

Caffeine
Quinolones may reduce the Cl of caffeine and prolong the t ½ .

Cyclosporine
Elevated plasma levels of cyclosporine have been reported with certain quinolones; therefore, monitor levels and adjust dose as needed.

Probenecid
May inhibit the tubular secretion of nalidixic acid, reducing the efficacy in treating UTIs and increasing the risk of side effects.

Theophylline
Theophylline plasma levels may be elevated by quinolones, increasing the risk of side effects.

1.一個月以下嬰兒及懷孕三個月以內之孕婦不得使用本劑。
2.繼續使用本劑一至二星期以上應作定期血液及肝臟機能試驗。
3.糖尿病患者於服用本劑期間檢驗尿糖時應採用試紙法，如Clinistix Test-tape等。