Choosing the Right Antibiotic for Bacterial Infections


Martin Cathrae; licensed via Creative Commons.

At a time when we have become so concerned about the overuse of antibiotics, doctors have become just as vigilant in only prescribed when needed. If they do so, they would 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 fatty layer that acts as a barrier against certain antibiotics

When choosing an antibiotic, your doctor would first consider the type of bacteria involved. This will determine, in part, which drugs can are most capable of penetrating the external barrier or damaging the structure enough to prevent it from replicating.

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 waxy layer 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 the 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, oral antibiotics are stronger than topical antibiotics. Intravenous antibiotics, by contrast, are stronger than both. But strength should only play a part in the selection of the right formulation. It is ultimately about the appropriateness of strength that matters more than just "hitting the infection hard."

The Course of Antibiotic Therapy

When it comes to antibiotics, the lesser the pill count the better. The simple fact is that people will usually stop taking an antibiotic as soon as they feel better. And that's a mistake. Not only does it 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.

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 other. 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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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  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.

Additional Reading

  • Infectious Disease Society of America (IDSA). "Implementing an Antibiotic Stewardship Program: Guidelines by the Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America." Clinical Infectious Diseases. 2016; 62;51-77.