What are antibiotics and how are they used?

Antibiotics are powerful drugs that are used to fight infections. Your healthcare team thinks you or your loved one might have an infection that can be treated with an antibiotic.

Not all infections are treated with antibiotics. While antibiotics may be effective against infections caused by bacteria (germs), they are not effective against viruses.

Like all drugs, antibiotics can have side effects and should be used only when necessary. Taking an antibiotic you don’t need can even be harmful. Because of this, there are important things to know about antibiotics.

What do I need to know about antibiotics?

Did you know:

  • Antibiotics are among the most commonly prescribed drugs. However, up to 50% of all the antibiotics prescribed for people are not needed nor as effective as hoped.
  • The overuse of antibiotics is the single most important factor that has led to antibiotic resistance.
  • Each year in the United States, at least 2 million people get serious infections with bacteria that are resistant to one or more of the antibiotics designed to treat those infections.
  • At least 23,000 people die each year as a direct result of these antibiotic-resistant infections. Almost 250,000 people each year need hospital care for treatment of Clostridium difficile (C. difficile) infections. This infection is very difficult to treat. The use of antibiotics was the main reason why the illness developed. At least 14,000 people die each year in the United States from C. difficile infections. Many of these infections could have been prevented.

The overuse or inappropriate use of antibiotics gives bacteria a chance to adapt. When this happens, the antibiotics no longer work as well to treat the infection – the bacteria become “resistant” to antibiotics.

What should I know about antibiotic safety?

Antibiotics are powerful drugs that are generally safe. They are very helpful in fighting disease, but sometimes antibiotics can actually be harmful.
Key facts to know about antibiotic safety:

  • Antibiotics can have side effects including allergic reactions and serious, possibly life-threatening diarrhea caused by the bacteria (germ) Clostridium difficile (C. diff). Antibiotics may also interfere with other drugs you may be taking.
  • Side effects of antibiotics are responsible for almost one out of five emergency department visits. They are the most common cause of emergency department visits for children under 18 years of age.
  • When you take an antibiotic you do not need, you are unnecessarily exposed to the side effects of the drug and do not get any benefit from it.

Taking an antibiotic you don’t need can lead to the development of antibiotic resistance. When resistance develops, antibiotics may not be able to stop future infections. Every time you take an antibiotic you don’t need, you increase your risk of developing a resistant infection in the future.
The bottom line: antibiotics come with benefits and risks. If you are prescribed an antibiotic, discuss the balance of benefits and risks with your healthcare team.

  • Allergic reactions: Every year, there are more than 140,000 emergency department visits for reactions to antibiotics. Almost four out of five emergency department visits for antibiotic-related side effects are due to an allergic reaction. These reactions can range from mild rashes and itching to serious blistering skin reactions, swelling of the face and throat, and breathing problems. Minimizing unnecessary antibiotic use is the best way to reduce the risk of side effects from antibiotics. You should tell your doctor about any past drug reactions or allergies.
  • C. difficile: C. difficile is a type of bacteria (germ) that causes diarrhea linked to at least 14,000 American deaths each year. When you take antibiotics, good bacteria that protect against infection are destroyed for several months. During this time, you can get sick from C. difficile. The bacteria can be picked up from contaminated surfaces or spread from the healthcare environment. People, especially older adults, are most at risk who take antibiotics and also get medical care. Take antibiotics exactly and only as prescribed.
  • Antibiotic resistance: The use of antibiotics may increase the risk of bacteria becoming resistant to them. Antibiotic-resistant infections can be very serious and difficult to treat.

What illnesses are caused by viruses and can’t be treated by antibiotics?

Viruses cause most upper respiratory infections, which include head colds, sore throats, bronchitis, and sinus infections. Viruses cannot be treated by antibiotics.

The common cold and flu (influenza) do not respond to antibiotics. Less than 10% of acute bronchitis cases are caused by bacteria. Most cases of acute ear infections also resolve without antibiotics.

Sore throats are usually caused by viruses as well. Antibiotics are not recommended unless you have strep throat. Only about 15% to 30% of sore throat cases in children and up to 10% of cases in adults are due to strep throat.

Almost all cases of acute bacterial sinusitis resolve without antibiotics.

The bottom line: Taking antibiotics for most acute upper respiratory tract infections does little or no good, and the downsides are real.

What’s making you sick: viruses or bacteria?

  • Cold/Runny Nose: Virus
    • Antibiotics needed: No
  • Bronchitis/Chest Cold (in otherwise healthy children and adults): Virus
    • Antibiotics needed: No
  • Whooping cough: Bacteria
    • Antibiotics needed: Yes
  • Flu: Virus
    • Antibiotics needed: No
  • Strep throat: Bacteria
    • Antibiotics needed: Yes
  • Sore throat (except strep): Virus
    • Antibiotics needed: No
  • Fluid in the Middle Ear (otitis media with effusion): Virus
    • Antibiotics needed: No
  • Urinary Tract Infection: Bacteria
    • Antibiotics needed: Yes

How are viruses treated?

Symptoms caused by viruses are usually treated with the over-the-counter drugs (drugs you can buy without a prescription). Some drugs reduce pain, such as acetaminophen (Tylenol®). Other drugs help make breathing easier (decongestants), and or relieve sneezing and runny nose (antihistamines). Symptoms can also be treated by gargling with salt water or drinking warm tea.

The best defense against getting the flu is to get a flu shot. The flu shot, however, does not protect against other viruses that cause other illnesses.

For some patients, a doctor may prescribe an antiviral drug, such as oseltamivir (Tamiflu®). These patients have a confirmed diagnosis of the flu and have risk factors for flu-related complications. These risk factors include:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Heart, liver or kidney disease
  • Age older than 65
  • Living in a nursing home
  • Weakened immune system due to cancer or HIV or organ transplantation – the immune system is the body’s defense system against infections

Although oseltamivir (Tamiflu®) does not “cure” the flu, it can shorten the amount of time with symptoms.

Finally, there are a few situations in which antibiotics are needed. See your healthcare provider if you have a weakened immune system due to cancer, or if you are taking steroids, have HIV, or have had an organ transplant. Also call if your symptoms worsen or last longer than 7 to 10 days.

If you think you may be getting the flu and you already have these conditions, you may be less able to fight bacterial infections should they occur.

How does my healthcare team know I need to take antibiotics?

The healthcare team may run tests to determine whether you need an antibiotic at all, and if so, which will work best. For example, your blood or urine may be checked for bacteria.

During treatment things may change. More tests and more information may show a different antibiotic is needed, or that this is a different type of infection. Tests may show that the antibiotic is not working. Or they may show an infection that cannot be treated with antibiotics.

Drug interactions

Antibiotics can interact with other drugs you take, making those drugs or the antibiotics less effective. Some drug combinations can worsen the side effects of the antibiotic or other drug. Common side effects of antibiotics include nausea, diarrhea, and stomach pain. Sometimes these symptoms can lead to dehydration and other problems. Ask your doctor about drug interactions and potential side effects of antibiotics. Notify your doctor right away if you have any side effects from antibiotics you are taking.

What questions should be asked about treatment with antibiotics?

It is important to understand what is happening with you or your loved one’s care. Here are a few important questions caregivers or patients should ask about antibiotic treatment:

  • What infection is this antibiotic treating? How does the healthcare team know that is the infection?
  • What side effects might occur from this antibiotic?
  • How long should these antibiotics be taken?
  • Are there special instructions on taking this antibiotic, such as which medications or supplements are safe to take with it, or if it should be taken with food?
  • What tests or monitoring will be done during treatment to show that the antibiotic is working?

Last reviewed by a Cleveland Clinic medical professional on 11/20/2016.


  • Centers for Disease Control and Prevention - Get Smart: Know When Antibiotics Work. Antibiotic Resistance Q and A (http://www.cdc.gov/getsmart/community/about/antibiotic-resistance-faqs.html)
  • Centers for Disease Control and Prevention - Get Smart: Know When Antibiotics Work. What Everyone Should Know (http://www.cdc.gov/getsmart/community/about/should-know.html)

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