Nalidixic acid

Nalidixic acid, a quinolone antibiotic, is effective against both gram-positive and gram-negative bacteria. Nalidixic acid acts in a bacteriostatic manner in lower concentrations and is bactericidal in higher concentrations. Nalidixic acid inhibits a subunit of DNA gyrase and topoisomerase IV and reversibly blocks DNA replication in susceptible bacteria^[1]. In Vitro: Nalidixic acid is against a variety of microorganisms, it is against with Escherichia coli, Pasteurella spp., Klebsiella pneuiiioniae, Aerobacter aeroyenes, Proteus spp., Salmonella spp., Shigella spp. and Brucella spp. with MIC values of 5.0-12.5 μg/ml, 0.5-2.5 μg/ml, 0.8-25.0 μg/ml, 1.0-25.0 μg/ml, 1.25-30.0 μg/ml, 8-3.2 μg/ml, and 7.5-10.0 μg/ml, respectively^[1].
In Vivo: The in vivo activity of Nalidixic acid is most pronounced against Gram-negative bacteria, while Gram-positive organisms are generally more resistant. Maximal activity is observed against systemic infections caused by E. coli, A. aerobacter, Proteus mirabilis, Shigella fkxneri, the ED₅₀ values are 25 mg/kg, 60 mg/kg, 50 mg/kg, and 62 mg/kg, respectively^[1].
The acute toxicity (LD₅₀) of Nalidixic acid in mice following oral and parenteral administration is: oral, 3300 mg/kg; intravenous, 176 mg/kg, and subcutaneous, 500 mg/kg^[1].