October 2, 2022

List of infections, side effects, prescription information

Antibiotics are medicines used to treat certain types of bacterial infections. They work to eliminate infections by killing bacteria or stopping their growth. They usually must be prescribed by a health care provider.

Learn more about the use of antibiotics, including when and how to take them safely.

Katleho Seisa/Getty Images

Antibiotic Information

Antibiotics were widely used in the 1940s, after British scientist Alexander Fleming discovered penicillin (the first antibiotic) in molds. Before Fleming began experimenting with penicillin, many people died from common bacterial infections.

Today, antibiotics are safe and effective for most people. They are usually prescribed to treat common bacterial infections, such as strep throat and urinary tract infections (UTIs).

Types and Forms

Antibiotics are divided into several classes based on their mode of action and the types of conditions they treat. Classes of antibiotics include:

  • Penicillinssuch as penicillin and Moxatag (amoxicillin)
  • Cephalosporinsas Keflex (cephalexin)
  • Beta-lactams with increased activityas Augmentin (amoxicillin with clavulanic acid)
  • Lincosamidesas Cleocin (clindamycin)
  • Macrolidessuch as Zithromax (azithromycin) and Erythrocin (erythromycin)
  • Fluoroquinolonesas Cipro (ciprofloxacin)
  • Trimethoprim-sulfamethoxazolebrand names include Bactrim and Septra
  • Urinary anti-infectivessuch as Furadantin (nitrofurantoin)
  • Tetracyclinessuch as Sumycin (tetracycline) and Vibramycin (doxycycline)

Antibiotics can be taken in different ways, including:

  • Topically (through ointments, drops, creams, or sprays)
  • By mouth (by capsule, liquid or tablet)
  • Injection
  • Intravenously (intravenously)

Usually, injection and IV antibiotics are used for more serious infections that have started to spread.

When are antibiotics prescribed?

It is not necessary to take antibiotics every time you have an illness. Antibiotics are most effective at treating certain bacterial infections, such as:

  • Urinary tract infections: Bacterial infections of the bladder and kidneys
  • Strep throat: A bacterial infection of the throat by group A Streptococcus pyogenes
  • Pertussis: An infection with the Whooping cough Bordetella bacteria that can be prevented by a vaccine
  • Certain sexually transmitted infections (STIs): including gonorrhea, chlamydiaand syphilis
  • Certain cases of pneumonia: An infection of the lungs which can be bacterial, in particular by Streptococcus pneumoniae and Haemophilus influenzae
  • Sepsis: A whole-body reaction to a blood infection

Some infections can be caused by either bacteria or viruses. Your health care provider will be able to determine if you have a viral or bacterial infection and prescribe (or not) antibiotics accordingly. They may also prescribe antibiotics if your infection seems to be getting worse or spreading.

Antibiotics cannot treat viral infections

It can be tempting to take antibiotics every time you’re sick. But antibiotics won’t treat conditions caused by viruses, such as:

  • Sore throat, except strep throat
  • Influenza (the flu)
  • Colds
  • Congestion and runny nose
  • Cough
  • Most cases of bronchitis (inflammation of the large airways)

Viral infections often go away without medical intervention or require antiviral drugs or other forms of treatment. Your healthcare provider can help you decide which treatment will be appropriate and effective for your infection.

Also, antibiotics only work to fight certain bacterial infections. They are not effective in treating all conditions caused by bacteria, including some ear infections and most sinus infections.

The problem of antibiotic resistance

Antibiotic resistant infections can occur when antibiotics are unable to kill certain bacteria. Antibiotic resistance can lead to serious health complications, such as organ failure. In some cases, it can even be fatal. There are more than 2.8 million antibiotic-resistant infections in the United States each year, resulting in more than 35,000 deaths.

You may be more likely to develop an antibiotic-resistant infection if you take them too often or unnecessarily. Only take antibiotics when you need them. Always complete your full course as prescribed (don’t stop when you feel better, continue the number of days on the prescription).

Taking Antibiotics Safely

Although antibiotics are safe and effective for most people, they can sometimes cause side effects. Here are some ways to make sure you’re taking antibiotics safely:

  • Take your antibiotics for exactly how long and at the exact dose prescribed by your healthcare professional.
  • Do not take antibiotics that have been prescribed for someone else.
  • Do not skip a dose or save your leftover antibiotics for later.
  • Do not give anyone else the antibiotics that have been prescribed for you.
  • Tell your health care provider right away if your symptoms get worse.

Allergy symptoms

Some people develop allergy symptoms after taking antibiotics. Allergic reactions to penicillins are particularly common – an estimated 5-15% of people are allergic to penicillin.

You may have an allergic reaction to an antibiotic if you have any of the following symptoms:

  • Eruption
  • Urticaria
  • Itching
  • Wheezing
  • Swelling
  • Difficulty breathing

If you start to experience any of these symptoms, stop taking the antibiotic immediately and tell your healthcare provider.

Severe allergic reaction

If you have symptoms of anaphylaxis (a severe allergic reaction) after taking antibiotics, such as difficulty breathing or swelling of your tongue or throat, dizziness, or fainting, seek immediate medical attention.

Other side effects

Apart from allergy symptoms, other common side effects of antibiotics can include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Headache
  • stomach pain
  • Black or hairy tongue
  • yeast infections

In rare cases, antibiotics can cause more serious side effects, including:

  • Worsening of signs of infection, such as fever
  • Articular pain
  • Severe diarrhea
  • Clostridioides difficile (C difference.) infections, which cause severe diarrhea that can be life-threatening

If you experience any of these symptoms seek medical attention immediately.

Antibiotics during pregnancy

Most antibiotics are safe to take during pregnancy. However, certain antibiotics, such as fluoroquinolones and tetracyclines, should be avoided if you are currently pregnant. Tell your health care provider if you are or might be pregnant before you start taking an antibiotic.

Pharmacy Options

Most of the time, antibiotics must be prescribed by a medical professional. However, some over-the-counter topical antibiotic treatments are available at pharmacies and drugstores.

Neosporin (neomycin, polymyxin, and bacitracin topical) is an over-the-counter antibiotic ointment used to prevent infection in wounds, cuts, and scrapes.

In some cases, Neosporin can cause an allergic skin reaction. Seek immediate medical attention if you notice any of the following symptoms:

  • Itching
  • Eruption
  • Urticaria
  • Difficulty breathing

Neosporin is only effective in treating minor skin lesions. Instead, talk to your health care provider if you have a burn, deep wound, animal bite, or other more serious injury.


Antibiotics are medicines that treat certain bacterial infections, either by killing the bacteria or by preventing their growth. Examples of common antibiotics include penicillin, azithromycin, clindamycin, and cephalexin.

Some of the conditions treated with antibiotics include strep throat, urinary tract infections (UTIs), and certain types of pneumonia and sexually transmitted infections (STIs). Antibiotics cannot treat infections caused by viruses, including colds, flu and runny nose.

It is important to take antibiotics exactly as prescribed by your healthcare professional. If you take antibiotics too often, you can develop antibiotic-resistant infections.

Common side effects of antibiotics include diarrhea, stomach pain, nausea, vomiting, headache, yeast infection, and black or hairy tongue. If you develop allergy symptoms such as rash, hives, swelling, or difficulty breathing after taking antibiotics, seek medical attention immediately.

A word from Verywell

If you have a bacterial infection, antibiotics can help you feel better and avoid life-threatening complications. However, it is important to only take antibiotics when you need them and exactly as prescribed.

Frequently Asked Questions

  • Do the antibiotics start working immediately?

    Antibiotics usually start working to eliminate a bacterial infection immediately. You might start feeling better in just one to three days. However, it is important to take your full course of antibiotics, even if your symptoms have already improved.

  • Can you get rid of a urinary tract infection without antibiotics?

    Many urinary tract infections (UTIs) go away on their own. According to some research, about 42% of UTIs go away on their own within the first nine days. If your UTI symptoms persist or worsen, you should see a doctor.

  • What are the most common types of antibiotics?

    Penicillin-type drugs, such as penicillin and amoxicillin, are among the most commonly prescribed antibiotics. Other common classes of antibiotics include cephalosporins (like cephalexin), macrolides (like azithromycin), and lincosamides (like clindamycin). All are used to treat bacterial infections, either by killing the bacteria or by preventing them from reproducing.

  • Can you get antibiotics at a walk-in clinic?

    Antibiotics can be prescribed by a doctor or other qualified health care provider at almost any walk-in clinic. Depending on the clinic and the type of antibiotic you need, you may be able to pick up your prescription there or at a local pharmacy. If you have a serious infection that requires intravenous (IV) antibiotics, you should seek emergency medical attention.