Pefloxacin Mesylate Dihydrate (1589 RB) , an antibacterial agent, restrains bacterial DNA replication by inhibiting DNA gyrase (topoisomerase).

Pefloxacin exerts potent bactericidal activity through several pathways and exhibits biphasic action: its killing effect decreases with increased concentration following initial rapid bactericidal activity. In bacterial cells cultured with Pefloxacin, the SOS response (non-replicative DNA repair) is induced, which inhibits replication, disrupts spindle formation, and blocks cell division, ultimately proving detrimental to bacteria by interfering with their morphological and biochemical properties. Similar to other quinolone antibiotics, Pefloxacin primarily targets bacterial DNA gyrase (topoisomerase II), a critical bacterial enzyme. It effectively inhibits members of the Enterobacteriaceae family (E. coli, Citrobacter, Klebsiella, Proteus, Morganella) with minimum inhibitory concentrations (MICs) ranging from 0.03 to 8 mg/L; for Shigella, Salmonella, and Yersinia, the MIC50/MIC90 values are 0.06/0.06, 0.12/1.0, and 0.12/0.25 mg/L respectively. Pefloxacin has weaker activity against Legionella pneumophila (MIC50/MIC90: 1.0/1.0 mg/L), very weak activity against Vibrio cholerae and Eikenella corrodes, and Listeria monocytogenes, Helicobacter pylori, and Nocardia asteroides show resistance with MIC50 ≥8 mg/L. Mycobacterial sensitivity to Pefloxacin varies from moderate to none, and most anaerobes are resistant. Rickettsiae and Chlamydiae are sensitive at treatable concentrations, while Mycoplasma and Ureaplasma show poor sensitivity (MIC50/MIC90: 2/8 mg/L). Pefloxacin's MICs for Gram-negative aerobes such as Alcaligenes, Pseudomonas aeruginosa, Acinetobacter, and Klebsiella range from 1 to 4 mg/L. For Gram-positive cocci, including coagulase-negative staphylococci and Staphylococcus aureus, even those resistant to other antibiotics, Pefloxacin maintains some sensitivity with MICs spanning 0.125 to 0.5 mg/L.