Polymyxin B is a lipopeptide antibiotic isolated from Bacillus polymyxa. Its basic structure consists of a polycationic peptide ring and a tripeptide side chain with a fatty acid tail. Polymyxin B is a mixture of at least four closely related components, polymyxin B1 to B4, with polymyxin B1 and B2 being the two major components. Polymyxin B acts on Gram-negative bacteria by interacting with lipopolysaccharide (LPS) of the outer membrane and destabilizing it. Polymyxin B is indicated for the treatment of many bacterial diseases such as meningeal infections, urinary tract infections and bacteremia.

Bacitracin is a polypeptide antibiotic produced by Bacillus subtilis and Bacillus licheniformis. Bacitracin in combination with neomycin and polymyxin B is indicated for the treatment of many bacterial diseases. The antibacterial properties of bacitracin are mediated by its binding to C55-isoprenyl pyrophosphate, resulting in inhibition of cell wall biosynthesis.

Kanamycin (a mixture of kanamycin A, B and C) is an aminoglycoside bacteriocidal antibiotic, available in oral, intravenous, and intramuscular forms, and used to treat a wide variety of infections. It is effective against Gram-negative bacteria and certain Gram-positive bacteria. Aminoglycosides work by binding to the bacterial 30S ribosomal subunit, causing misreading of t-RNA, leaving the bacterium unable to synthesize proteins vital to its growth. Serious side effects include tinnitus or loss of hearing, toxicity to kidneys, and allergic reactions to the drug. Mixing of an aminoglycoside with beta-lactam-type antibiotics (penicillins or cephalosporins) may result in a significant mutual inactivation. Even when an aminoglycoside and a penicillin-type drug are administered separately by different routes, a reduction in aminoglycoside serum half-life or serum levels has been reported in patients with impaired renal function and in some patients with normal renal function.

Spiramycin, a macrolide antibiotic, has been studied in the United States for the treatment of cryptosporidial diarrhea. Some reports suggest that spiramycin is useful in improving the symptoms of cryptosporidial diarrhea in some patients. It has been used in Europe and Canada for over 20 years to treat bacterial infections. Serious adverse effects from spiramycin are apparently rare, and no drug-associated deaths have been reported. Spiramycin inhibits translocation by binding to bacterial 50S ribosomal subunits with an apparent 1:1 stoichiometry. This antibiotic is a potent inhibitor of the binding to the ribosome of both donor and acceptor substrates. Spiramycin induces rapid breakdown of polyribosomes, an effect which has formerly been interpreted as occurring by normal ribosomal run-off followed by an antibiotic-induced block at or shortly after initiation of a new peptide. However, there is now convincing evidence that spiramycin, and probably all macrolides, act primarily by stimulating the dissociation of peptidyl-tRNA from ribosomes during translocation

Ceftaroline is a fifth-generation broad-spectrum cephalosporin with potent antimicrobial activity against Gram-positive and Gram-negative pathogens. Ceftaroline is the bioactive metabolite of ceftaroline fosamil, an N-phosphonoamino water-soluble cephalosporin prodrug, which is rapidly converted in vivo upon the hydrolysis of the phosphonate group by plasma phosphatises. Ceftaroline fosamil is being developed by Forest Laboratories, under a license from Takeda. In 2010, the U.S. Food and Drug Administration (FDA) approved ceftaroline fosamil for use in the treatment of acute bacterial skin and skin structure infections as well as community-acquired pneumonia. Ceftaroline has bactericidal activity against methicillin-resistant Staphylococcus aureus, therefore serving as an attractive alternative agent for the treatment of methicillin-resistant Staphylococcus aureus bacteremia when approved agents are contraindicated or treatment failures have occurred. Like other β-lactams, ceftaroline’s mechanism of action is mediated by binding to the penicillin-binding protein (PBP), the enzyme mediating the cross-linking transpeptidation of the peptidoglycan which are the terminal steps in completing formation of the bacterial cell wall. MRSA strains have a mutated PBP2a which prohibits β-lactam antibiotics from accessing its active site that mediates the transpeptidation reaction. Ceftaroline possesses an ethoxyimino side-chain mimicking a portion of a cell wall structure, which acts as a “Trojan horse”, allosterically opening and facilitating access to the active site of the PBP2a. Based on clinical trial data to date, ceftaroline appears to be safe and well-tolerated. Since ceftaroline is a cephalosporin, it has caused serious hypersensitivity reactions in patients who are allergic to cephalosporins and among some patients with penicillin allergies.

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.

Meropenem (generic name: meropenem hydrate) is a carbapenem antibiotic for injection showing a strong antibacterial activity to a wide range of bacteria strains from Gram-positive bacteria, Gram-negative bacteria to anaerobic bacteria. It is used as single agent therapy for the treatment of the following infections: complicated skin and skin structure infections due to Staphylococcus aureus (b-lactamase and non-b-lactamase producing, methicillin-susceptible isolates only), Streptococcus pyogenes, Streptococcus agalactiae, viridans group streptococci. This drug also used in case of Intra-abdominal Infections for the treatment complicated appendicitis and peritonitis caused by viridans group streptococci, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Bacteroides fragilis, B. thetaiotaomicron, and Peptostreptococcus species. In addition is used the treatment of bacterial meningitis caused by Streptococcus pneumoniae, Haemophilus influenzae (b-lactamase and non-b-lactamase-producing isolates), and Neisseria meningitides. The bactericidal activity of meropenem results from the inhibition of cell wall synthesis. Meropenem readily penetrates the cell wall of most Gram-positive and Gram-negative bacteria to reach penicillin-binding-protein (PBP) targets. Its strongest affinities are toward PBPs 2, 3 and 4 of Escherichia coli and Pseudomonas aeruginosa; and PBPs 1, 2 and 4 of Staphylococcus aureus. Meropenem has significant stability to hydrolysis by β-lactamases, both penicillinases and cephalosporinases produced by Gram-positive and Gram-negative bacteria. Meropenem should not be used to treat methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus epidermidis (MRSE). Meropenem product with such superior effectiveness and safety has been approved for marketing by 100 countries or more in the world (as of March 2004) since its first launch in Italy in 1994.

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.