In vitro activity: Pefloxacin like that of other quinolones mainly targets bacterial DNA gyrase (topoisomerase II) which is an essential bacterial enzyme with a variety of activities. Pefloxacin is a strongly bactericidal in a complex manner; the bactericidal effect has been described as 'biphasic' with a single rapidly killing effect followed by a paradoxical reduced killing phase in the presence of increased concentration; in bacterial cells incubated with Pefloxacin, non-replicative DNA synthesis (DNA repair), termed SOS response, is induced and SOS response prevents replication, blocking cell division and producing filarnentation. Thus the end result of the SOS response is harmful for the bacteria with morphological and biochemical disturbances. Pefloxacin is highly active against the Enterobacteriaceae (Citrobacter, Enterobacter, Klebsiella, Morganella, Proteus); the minimal inhibitory concentrations (MICs) of Pefloxacin for all genus and species of this family of bacteria ranges usually between 0.03 and 4 or 8 mg/L; against Salmonella, Shigella and Yersinia the MIC50/MIC90 are lower: 0.12/1.0, 0.06/0.06, 0.12/0.25 mg/L, respectively. The MICs of Pefloxacin for Gram- negative aerobic bacilli, such as Pseudomonas aeruginosa, Acinetobacter spp., Alcaligenes, Pseudomonas spp. , ranges from 1 to 4 mg/L. Gram-positive cocci Staphylococci including S. aureus and coagulase-negative staphylococci even resistant to other antibiotics are susceptible or moderately susceptible to Pefloxacin, with MICs in the range 0.125-0.5 mg/L. The MICs of Pefloxacin for Legionella pneumophila are moderately low (MIC50/MIC90:1.0/1.0mg/L); for Eikenella corrodens, Vibrio cholerae, the MICs are very low, whereas Helicobacter pylori, Listeria monocytogenes and Nocardia astero'ides are resistant to Pefloxacin, with MIC50 of 8 mg/L or more.Mycobacteria are moderately or not susceptible to Pefloxacin and most anaerobes are resistant to Pefloxacin. Mycoplasma spp and Chlamydiae are poorly susceptible to Pefloxacin (MIC50/MIC90: 2/8 mg/L) whereas Rickettsia conori and Coxiella burneti are susceptible at therapeutically achievable concentrations.

Int J Antimicrob Agents. 1991;1(1):29-46.