Gatifloxacin is a recently developed antibacterial agent differing from earlier fluoroquinolones by the presence of a methoxy group at the C-8 position. The presence of the methoxy group has conferred improved antibacterial activity against both Gram-positive and Gram-negative organisms, making gatifloxacin a broad-spectrum antimicrobial agent applicable in many clinical settings. Gatifloxacin is sold under the brand Zymar and is indicated for the treatment of bacterial conjunctivitis caused by susceptible strains of the following organisms: Aerobic Gram-Positive Bacteria: Cornyebacterium propinquum, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mitis, Streptococcus pneumoniae and Aerobic Gram-Negative Bacteria: Haemophilus influenza. The antibacterial action depends on blocking of bacterial DNA replication by binding itself to an enzyme called DNA gyrase, which allows the untwisting required to replicate one DNA double helix into two. Notably the drug has 100 times higher affinity for bacterial DNA gyrase than for mammalian. In addition, Gatifloxacin inhibits bacterial topoisomerase IV. This enzyme is an enzyme known to play a key role in the partitioning of the chromosomal DNA during bacterial cell division. The mechanism of action of fluoroquinolones including gatifloxacin is different from that of aminoglycoside, macrolide, and tetracycline antibiotics. Therefore, gatifloxacin may be active against pathogens that are resistant to these antibiotics and these antibiotics may be active against pathogens that are resistant to gatifloxacin. There is no cross-resistance between gatifloxacin and the aforementioned classes of antibiotics. Cross-resistance has been observed between systemic gatifloxacin and some other fluoroquinolones.

Levofloxacin is the L-isomer of the racemate, ofloxacin, a quinolone antimicrobial agent. Levofloxacin is used for oral and intravenous administration. Levofloxacin is sold under brand name levaquin and is used to treat infections in adults (≥18 years of age) caused by designated, susceptible bacteria such as, pneumonia: nosocomial and community acquired; skin and skin structure infections: complicated and uncomplicated; chronic bacterial prostatitis; inhalational anthrax. In addition this drug is used to treat plague; urinary tract infections: complicated and uncomplicated; acute pyelonephritis; acute bacterial exacerbation of chronic bronchitis and acute bacterial sinusitis. Levofloxacin, like other fluoroquinolones, inhibits the bacterial DNA gyrase, halting DNA replication. This results in strand breakage on a bacterial chromosome, supercoiling, and resealing. In addition, levofloxacin inhibits a bacterial type II topoisomerase.

Sarafloxacin [A 55620] is a quinolone antibiotic that was under development with Abbott Laboratories in the USA. It was removed from clinical use by its manufacturer Abbott Laboratories from April 30, 2001. It was never approved for use in the US or Canada.

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.

Orbifloxacin (brand name Orbax) is a fluoroquinolone antibiotic which is approved for use in dogs and cats, abd marketed by Schering-Plough Animal Health. Orbifloxacin is a synthetic broad-spectrum antibacterial agent from the class of fluoroquinolone carboxylic acid derivatives. Orbifloxacin is the international nonproprietary name for 1-cyclopropyl-5,6,8-trifluoro-1,4-dihydro-7-(cis-3,5-dimethyl-1-piperazinyl)-4-oxoquinoline-3-carboxylic acid. ORBAX® Oral Suspension is a malt flavored antibiotic suspension containing 30 mg/mL of orbifloxacin and sorbic acid as a preservative. ORBAX® Oral Suspension is indicated for the treatment of urinary tract infections (cystitis) and also for skin and soft tissue infections (wounds and abscesses). Orbifloxacin is bactericidal against a wide range of gram-negative and gram-positive organisms and exerts its antibacterial effect through interference with the bacterial enzyme DNA gyrase which is needed for the maintenance and synthesis of bacterial DNA.

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.

Nadifloxacin (INN, brand names Acuatim, Nadiflox, Nadoxin, Nadixa, activon) is a topical fluoroquinolone antibiotic for the treatment of acne vulgaris. It is also used to treat bacterial skin infections. In vitro studies of nadifloxacin showed potent and broad-spectrum antibacterial activity against aerobic Gram-positive, Gram-negative and anaerobic bacteria, including Propionibacterium acnes and Staphylococcus epidermidis. Nadifloxacin inhibits the enzyme DNA gyrase that is involved in bacterial DNA synthesis and replication, thus inhibiting the bacterial multiplication. In some European countries, the drug has been approved for the treatment of acne vulgaris. In a 2013 multicenter, randomized clinical study with a total of 184 Japanese patients with moderate to severe acne, adapalene 0.1% gel plus nadifloxacin 1% cream (combination therapy) showed a significant efficacy in decrement of inflammatory papulopustular lesions. Despite this it should be noted that in patients with skin lesions, topical application of nadifloxacin can result in plasma concentrations of 1 to 3 ng/ml. During the treatment some patients may develop some adverse effects predominantly of the skin and subcutaneous tissue: burning and itching (in absolute the most common side effect), contact dermatitis, dryness and skin irritation.

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.

Rosoxacin, a quinolone derivative, is an antibiotic, which is used for the treatment of uncomplicated acute gonococcal urethritis. Administration of rosoxacin is an effective regimen for the therapy of chancroid and is a reasonable alternative to other short-course regimens. The drug binds to and inhibits two enzymes topoisomerase II (DNA gyrase), which is required for bacterial DNA replication, transcription, repair, and recombination.