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Choosing the Right Antibiotic for Bacterial Infections


Updated June 05, 2014

With so many different kinds of antibiotics available, how does your healthcare provider know which to prescribe? To determine the appropriate antibiotic for your infection, your doctor should consider the following questions:

  1. Does the prescribed antibiotic kill the bacterium or merely stop it from dividing?
    Antibiotics are divided into two categories. “Bactericidal” antibiotics effectively kill bacteria, whereas “bacteriostatic” antibiotics do not kill the bacteria, but stop them from growing. For some infections, limiting bacterial growth is sufficient to allow the body’s natural defenses (i.e. white blood cells and antibodies) to eliminate the infection.

  2. What type of bacteria does it target?
    Bacteria are divided into two types, depending on their external structure. Gram-positive bacteria have thick waxy layers, whereas gram-negative bacteria have an extra fatty layer that can act as a barrier against some antibiotics. It is important to understand these structures in order to determine which antibiotics can pass through the barrier. Some classes of antibiotics can also target these external structures, damaging them enough to either stop their growth or to kill them.

  3. Which parts of the bacteria does it target? The different classes of antibiotics are divided according to the part of the bacterium that is targeted. For example, all antibiotics in the penicillin class (ampicillin, amoxicillin, etc.) block the formation of the external waxy layer of some bacteria. Other classes of antibiotics target other essential parts of the bacteria, including components necessary for its structure, cell division, and protein synthesis.

  4. How is the antibiotic applied? Depending on the type of infection, the application of the antibiotic will differ. Eye infections can sometimes be treated with antibiotic eye drops, and cuts and scrapes can be treated with topical antibiotic ointments. Other bacterial infections, such as urinary tract infections or pneumonia, can be treated with antibiotic pills.

  5. How long should the antibiotic be used? Each type of antibiotic will be different for each kind of infection. Careful clinical studies have been conducted in order to guide physicians toward knowing how long a patient should receive a given antibiotic. Antibiotics work by eliminating (or stopping the growth of) the majority of bacteria during an infection and allowing the body’s natural defenses to take care of the rest. By not taking the correct amount of antibiotics, surviving bacteria may continue to grow, causing a recurrent infection. Even worse, those that survive may become antibiotic-resistant (see superbugs), resulting in a more dangerous and often fatal disease in which treatment is much more difficult to manage.


    Antibiotics. Medline Plus. US National Library of Medicine and National Institutes of Health.

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