Antibiotics for Gram Negative Bacteria

Page content

In human beings, many of the severe infectious diseases are caused by gram negative bacteria. When the era of antibiotics commenced with the discovery of penicillin, it was found that most of the penicillin-based antibiotic derivatives were ineffective against gram negative bacterial infections. This lead to the discovery and development of antibiotics for gram negative bacteria caused infections. In this article, information is provided on the different classes of antibiotics available, their uses, the bacteria they are active against and the possible adverse side-effects.

Different Groups of Antibiotics, Their Uses and Side-effects

The most commonly used antibiotics to treat infections caused by gram negative bacteria include the following classes:

a) Aminoglycosides: This class includes amikacin, gentamicin, kanamycin, neomycin, streptomycin and tobramycin. These are used to treat infections caused by Escherichia coli and bacteria belonging to the Klebsiella species. Aminoglycosides are combined with cephalosporins to give a more efficient activity against gram negative bacterial infections. They are administered through injections and can’t be taken orally since stomach acids tend to destroy them easily. Some of the adverse side-effects are loss of hearing due to ear damage, spells of dizziness and kidney damage. To avoid effects, they are usually given on a short-term basis.

b) Cephalosporins: Cephalosporins have been divided into first, second, third and fourth “generations” based on both their antimicrobial properties and chronology. At present, a fifth generation has been introduced. Every new generation possesses higher activity against gram negative infections.

First generation cephalosporins include cefadroxil, cefazolin and cephalexin. They are used in the treatment of skin as well as soft-tissue infections. Their adverse side-effects include gastrointestinal problems like diarrhea, nausea and allergic reactions.

Second generation cephalosporins include cefaclor, cefoxitin, cefprozil, cefuroxime and loracarbef. They are used in the treatment of certain respiratory and stomach infections. Their adverse side-effects are stomach upsets, diarrhea, nausea and allergic reactions.

Third generation cephalosporins include cefixime, cefdinir, cefditoren, cefoperazone, cefotaxime and cefpodoxime. They are used orally to treat a wide range of gram negative bacterial infections. Injectable forms are used in the treatment of hospital acquired infections like meningitis. Their adverse side-effects are stomach upsets, diarrhea, nausea and allergic reactions.

Fourth generation cephalosporins like cefepime are used to treat severe Pseudomonas infections in patients who have weak immunity or suffer from infections by bacteria resistant to the first three generations of cephalosporins. Their adverse effects are the same as the other cephalosporins.

Fifth generation cephalosporins like ceftobiprole are prescribed for treatment of serious skin infections, especially in diabetic patients. It is also used to treat infections caused by Escherichia coli, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) which are one of the most prominent public health issues today.

c) Monobactams: This class includes aztreonam, used in the treatment of a broad range of gram negative bacterial infections in people who have allergies to antibiotics like cephalosporins.

d) Several miscellaneous antibiotics are used to treat gram negative bacterial infections such as linezolid. Linezolid is prescribed sparingly because it has several adverse side-effects such as nausea, headaches, diarrhea, anemia accompanied by severely decreased white blood cell and platelet counts, visual impairments and peripheral neuropathy. In some patients the side-effects have even included tremors. This medicine is contraindicated in individuals who have been prescribed selective serotonin-release inhibitors (SSRIs) as it causes the patient to go into comas.

Due to the ever-increasing problem of antibiotic resistance in bacteria, new antibiotics for gram negative bacteria have to be discovered and developed to combat this public health problem.


“Antibiotics”. (2008). Retrieved on May 18th, 2011 from:

Evans M E, Feola D J, Rapp R P. Polymyxin B sulfate and colistin: old antibiotics for emerging multiresistant gram-negative bacteria. Ann Pharmacother. 1999; 33:960–967.

Falagas ME, Kasiakou SK. Colistin: the revival of polymyxins for the management of multidrug-resistant gram-negative bacterial infections. Clin Infect Dis 2005; 40:1333-41.