Clinafloxacin is a broad-spectrum fluoroquinolone antibiotic that was originally developed and subsequently abandoned in the late 1990s as a human health antibiotic for respiratory diseases. Clinafloxacin displays broad-spectrum antibacterial activity against Gram-positive, Gram-negative, and anaerobic pathogens by inhibiting the bacterial regulatory enzyme DNA gyrase (IC50 = 0.92 ug/ml) as well as topoisomerase IV (IC50 = 1.62 ug/ml).

Gemifloxacin is an oral broad-spectrum quinolone antibacterial agent used in the treatment of acute bacterial exacerbation of chronic bronchitis and mild-to-moderate pneumonia. Gemifloxacin mesylate is marketed under the brand name Factive, indicated for the treatment of bacterial infection caused by susceptible strains such as S. pneumoniae, H. influenzae, H. parainfluenzae, or M. catarrhalis, S. pneumoniae (including multi-drug resistant strains [MDRSP]), M. pneumoniae, C. pneumoniae, or K. pneumoniae. Gemifloxacin has in vitro activity against a wide range of Gram-negative and Grampositive microorganisms. Gemifloxacin is bactericidal with minimum bactericidal concentrations (MBCs) generally within one dilution of the minimum inhibitory concentrations (MICs). Gemifloxacin acts by inhibiting DNA synthesis through the inhibition of both DNA gyrase and topoisomerase IV (TOPO IV), which are essential for bacterial growth. Streptococcus pneumoniae showing mutations in both DNA gyrase and TOPO IV (double mutants) are resistant to most fluoroquinolones. Gemifloxacin has the ability to inhibit both enzyme systems at therapeutically relevant drug levels in S. pneumoniae (dual targeting), and has MIC values that are still in the susceptible range for some of these double mutants.

Pefloxacin is a fluorinated quinolone that is structurally related to nalidixic acid. It can be administered both orally and intravenously, and has a broad spectrum of in vitro activity against Gram-negative organisms and staphylococci. The bactericidal action of pefloxacin results from interference with the activity of the bacterial enzymes DNA gyrase and topoisomerase IV, which are needed for the transcription and replication of bacterial DNA. DNA gyrase appears to be the primary quinolone target for gram-negative bacteria. Topoisomerase IV appears to be the preferential target in gram-positive organisms. Interference with these two topoisomerases results in strand breakage of the bacterial chromosome, supercoiling, and resealing. As a result DNA replication and transcription is inhibited. It is prescribed for the treatment of uncomplicated gonococcal urethritis in males and for gram-negative bacterial infections in gastrointestinal system and genitourinary tract.

Pefloxacin is a fluorinated quinolone that is structurally related to nalidixic acid. It can be administered both orally and intravenously, and has a broad spectrum of in vitro activity against Gram-negative organisms and staphylococci. The bactericidal action of pefloxacin results from interference with the activity of the bacterial enzymes DNA gyrase and topoisomerase IV, which are needed for the transcription and replication of bacterial DNA. DNA gyrase appears to be the primary quinolone target for gram-negative bacteria. Topoisomerase IV appears to be the preferential target in gram-positive organisms. Interference with these two topoisomerases results in strand breakage of the bacterial chromosome, supercoiling, and resealing. As a result DNA replication and transcription is inhibited. It is prescribed for the treatment of uncomplicated gonococcal urethritis in males and for gram-negative bacterial infections in gastrointestinal system and genitourinary tract.

Sitafloxacin hydrate (DU-6859a, Gracevit), a new-generation, broad-spectrum oral fluoroquinolone that is very active against many Gram-positive, Gram-negative and anaerobic clinical isolates, including strains resistant to other fluoroquinolones, was recently approved in Japan for the treatment of respiratory and urinary tract infections. This is a new quinolone oral antibacterial to inhibit DNA replication of bacteria at the time of infection, and shows antibacterial action. Sitafloxacin is active against methicillin-resistant staphylococci, Streptococcus pneumoniae and other streptococci with reduced susceptibility to levofloxacin and other quinolones and enterococci. Sitafloxacin has also demonstrated activity against clinical isolates of Klebsiella pneumoniae (including about 67% of strains producing extended-spectrum, beta-lactamases and resistant to ciprofloxacin), Enterobacter cloacae, Pseudomonas aeruginosa with some activity against quinolone-resistant strains and Acinetobacter baumannii. The in vitro activity against anaerobes is comparable to imipenem or metronidazole. Sitafloxacin showed dual inhibitory activity against both enzymes: Streptococcus pneumoniae DNA gyrase and topoisomerase IV.

Sitafloxacin hydrate (DU-6859a, Gracevit), a new-generation, broad-spectrum oral fluoroquinolone that is very active against many Gram-positive, Gram-negative and anaerobic clinical isolates, including strains resistant to other fluoroquinolones, was recently approved in Japan for the treatment of respiratory and urinary tract infections. This is a new quinolone oral antibacterial to inhibit DNA replication of bacteria at the time of infection, and shows antibacterial action. Sitafloxacin is active against methicillin-resistant staphylococci, Streptococcus pneumoniae and other streptococci with reduced susceptibility to levofloxacin and other quinolones and enterococci. Sitafloxacin has also demonstrated activity against clinical isolates of Klebsiella pneumoniae (including about 67% of strains producing extended-spectrum, beta-lactamases and resistant to ciprofloxacin), Enterobacter cloacae, Pseudomonas aeruginosa with some activity against quinolone-resistant strains and Acinetobacter baumannii. The in vitro activity against anaerobes is comparable to imipenem or metronidazole. Sitafloxacin showed dual inhibitory activity against both enzymes: Streptococcus pneumoniae DNA gyrase and topoisomerase IV.