Choosing the Right Antibiotic for Bacterial Infections

Antibiotics

Martin Cathrae; licensed via Creative Commons.

At a time when we have become so concerned about the overuse of antibiotics, doctors have to become just as vigilant in only prescribing them when needed. To do so, they would need to make their selection based on five basic criteria: effectiveness, appropriateness, cost, ease of use, and avoidance of side effects.

To determine the antibiotic appropriate to your infection, your doctor would consider the following:

The Type of Bacteria Involved

Bacteria are divided into two types depending on their external structure:

  • Gram-positive bacteria which has thick, waxy external layer
  • Gram-negative bacteria which has an extra lipid layer that acts as a barrier against certain antibiotics

When choosing an antibiotic, your doctor first considers the type of bacteria involved. The type of bacteria can help determine which antibiotic drugs to choose, since not all antibiotics affect all bacteria.

The Action of the Antibiotic

The different classes of antibiotics are divided according to the part of the bacterium they affect. For example, all penicillin-class antibiotics (ampicillin, amoxicillin) block the formation of the external cell wall of the bacteria. Other classes attack the replication cycle of the bacteria, including cell division and protein synthesis needed to reproduce.

Antibiotics are further divided into bactericidal antibiotics (which kill bacteria) and bacteriostatic antibiotics (which stop them from growing). For some infections, limiting bacterial growth is sufficient enough to allow the body’s natural defenses to fully eradicate the bacteria.

How the Antibiotic Is Administered

Depending on the type and location of the infection, the choice of antibiotic will differ. Eye infections can often be treated with antibiotic eye drops while cuts and scrapes can be relieved with topical ointments. Other infections, such as urinary tract infections or pneumonia, may require pills.

As a general rule, topical antibiotics are suitable for some specific infections at localized sites (like an infected cut, or some eye infections) whereas oral and intravenous antibiotics are needed for more severe and systemic infections. For the most severe infections (requiring hospitalization), intravenous antibiotics are usually but not always required.

The Course of Antibiotic Therapy

When it comes to antibiotics, getting the proper duration of the correct antibiotic safely is the priority. However, the simple fact is that people will usually stop taking an antibiotic as soon as they start feeling better. And that's a mistake. Not only does not finishing the full course increase the likelihood of recurrence, but it also promotes the development of drug resistance.

Antibiotics work by eliminating the majority of bacteria while allowing the immune system to take care of the rest. By not completing a course of antibiotics, the surviving bacteria have the opportunity to thrive, some of which may be fully or partially resistant to the antibiotic. If these are allowed to predominate, antibiotic-resistant strains and superbugs can develop.

Whether You Actually Need Antibiotics

Ultimately the most important question everyone should ask is: Do you really need a course of antibiotics to treat your infection?

Generally speaking, you do not need an antibiotic every time you have an infection or might have an infection. They are not there to take "just in case" or to save for another occasion if you cut your treatment short. Both are bad ideas. Antibiotics do not work for colds or most upper respiratory infections.

Focus instead on avoiding infections by following three simple tips: 

  • Get vaccinated for both bacterial and viral infections. Speak with your doctor about which ones you need or are missing.
  • Wash your hands. This is not about being germ-phobic. It's about understanding that your hands are among the most effective vectors of infection. Wash thoroughly, ideally with an antibacterial wash, whenever you are in a public place where you might pick up a bug.
  • Cover your mouth when you sneeze or a cough. Try to avoid doing so into your hands as this can spread an infection to others. Instead, use a tissue or the crook of your elbow. If in a confined space such as an airplane, consider wearing a disposable mask if you are ill or at risk of infection.
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  1. Leekha S, Terrell CL, Edson RS. General principles of antimicrobial therapyMayo Clin Proc. 2011;86(2):156–167. doi:10.4065/mcp.2010.0639

  2. World Health Organization. Antibiotic resistance. Updated February 5, 2018.

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