Antibiotics are medications that treat bacterial infections. They achieve this by killing bacteria or slowing their growth. Some common types of antibiotics include penicillin and macrolides.

Medical professionals typically use some types of antibiotics more often than others. This is due to the variety of bacteria these types of antibiotics are effective against. Different antibiotics use different methods to destroy bacteria and treat the infection. As such, some specific antibiotics can be more effective against certain bacterial infections.

Some antibiotics may also work better to treat certain infections depending on where the infection is in the body. Additionally, a doctor may start using a broad-spectrum antibiotic, which can treat multiple strains of bacteria. After taking a culture to test for bacteria, they can then change the antibiotic to treat specific bacteria.

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Bottles of antibiotics line a shelf at a Publix Supermarket pharmacy August 7, 2007 in Miami, Florida. Image credit: Joe Raedle/Getty Images

Penicillin was the first antibiotic that scientists discovered and remains a versatile tool in the treatment of bacterial infections. The term penicillins also refers to other antibiotics that work in a similar way.

Penicillins work by breaking down the walls of bacterial cells, allowing water to enter and destroy the cell.

Doctors prescribe penicillins for many different infections, including:

Healthcare professionals will administer penicillins either as an oral pill or intravenously through a vein. Common types of penicillins include:

  • amoxicillin
  • ampicillin
  • dicloxacillin
  • nafcillin
  • oxacillin
  • penicillin V
  • penicillin G
  • piperacillin

Adverse effects can include:

  • nausea
  • vomiting
  • diarrhea
  • rash
  • abdominal pain
  • headaches
  • high potassium

People may also be allergic to penicillins, which can cause hives, low blood pressure, and breathing problems.

Doctors often prescribe cephalosporins to those who have an allergy to penicillin. They work in a similar way to penicillin, preventing the bacterial cells from forming sturdy walls.

People can take them to treat skin infections, epididymitis, cellulitis, abscesses, meningitis, and bacteria resistant to other antibiotics. Some cephalosporins are effective against severe infections, such as septicemia.

There are several cephalosporins, including:

  • cefaclor
  • cefadroxil
  • cefazolin
  • cefixime
  • cefoxitin
  • cefuroxime
  • cephalexin

Side effects might include:

Tetracyclines block bacterial cells from reproducing by slowing or stopping the manufacture of their proteins. They also have anti-inflammatory properties. People can take tetracyclines to treat:

These include:

Children and pregnant people may want to avoid taking tetracycline as it can cause teeth discoloration in fetuses and young children. Other side effects may include:

  • abdominal pain and discomfort
  • nausea
  • vomiting
  • anorexia
  • photosensitivity

It is important not to take these with diuretics, or water pills, as this may increase the risk of kidney toxicity. As the kidneys remove the drug through waste, it is also unsuitable for people with kidney failure.

Macrolides occur naturally and derive from plants and microorganisms. Like tetracyclines, they block a bacteria’s production of proteins. Doctors often prescribe macrolides to treat bacterial infections that are resistant to other antibiotics for those with allergies. However, they are currently the first choice of treatment for atypical pneumonia.

Common macrolides include:

They can help treat a range of bacterial conditions, including:

People taking the following medications may need to adjust or change their prescription if it is necessary to take macrolides, as they can interact with:

Side effects might include:

  • nausea and vomiting
  • abdominal pain
  • diarrhea
  • cardiac arrhythmias
  • hearing loss

Additionally, pregnant people and their children may experience side effects from taking macrolides, especially erythromycin.

These antibiotics act against several species of bacteria, including Staphylococci, Streptococcus, Enterococcus, Listeria, and Nocardia. They work by preventing bacteria from copying their DNA and carrying out their function.

Fluoroquinolones are a recommended first-line treatment for:

  • prostatitis
  • severe salmonellosis
  • epididymitis due to urinary bacteria

They also work for several other conditions, such as:

  • bacterial bronchitis
  • pneumonia
  • sinusitis
  • UTIs
  • septicemia
  • joint and bone infections
  • skin infections

However, doctors use caution when prescribing this class of antibiotics, as they have links to increased bacterial resistance. They will usually only prescribe them for severe, life threatening, or stubborn infections.

This class of antibiotics includes:

The following adverse effects might occur due to taking fluoroquinolones:

  • nausea
  • vomiting
  • abdominal pain
  • taste changes
  • rarely, tendon ruptures and aortic aneurysm
  • photosensitivity

Also known as sulfa drugs, these are synthetic antibiotics that stop bacteria from using folic acid to make DNA. This blocks their ability to reproduce. Doctors prescribe sulfonamides to treat a range of infections, including:

  • tonsillitis
  • septicemia
  • meningococcal meningitis
  • bacillary dysentery
  • UTIs
  • infected burns
  • salmonellosis
  • E. coli infections
  • eye infections
  • skin conditions

Several sulfonamides are available in the United States, including:

  • sulfasalazine
  • sulfamethoxazole, which is only available in combination with trimethoprim
  • sulfacetamide
  • silver sulfadiazine

Some adverse effects of sulfonamides might include:

Evidence suggests that sulfonamides may affect fetal development during pregnancy. As such, if a doctor suggests sulfonamides for a pregnant individual, they will carefully monitor for potential side effects.

Glycopeptides are fully or partially synthetic drugs, which are modified natural substances with heightened effectiveness against bacteria. These disrupt how bacteria build cell walls, leading to cell death.

They are particularly effective against bacteria that have become resistant to other antibiotics, such as Streptococcus pneumoniae or Staphylococcus aureus. Doctors also prescribe them to treat:

Glycopeptides available in the United States include:

  • dalbavancin
  • oritavancin
  • telavancin

Side effects might include:

Below are answers to common questions about antibiotics and antibiotic resistance.

What is antibiotic resistance?

Bacteria can learn from unnecessary or over-frequent exposure to antibiotics and develop immunity to certain antibacterial drugs. Inappropriately using antibiotics can allow bacteria to adapt and learn how to make specific proteins that counter the drug.

They may then pass resistant traits along to other bacteria in their DNA. This makes the infection as a whole harder to treat.

How can people prevent antibiotic resistance?

The best way to reduce antibiotic resistance is to take them as a doctor prescribes. Some people may consider stopping antibiotics once they feel better, but they should always finish the course of antibiotics.

People can also reduce antibiotic resistance by avoiding misuse or unnecessary antibiotic use.

Some individuals misuse antibiotics by taking the wrong antibiotics, taking the wrong amounts, or taking them for the wrong duration. Others may use antibiotics when they are not going to have an effect, such as for infections by viruses or parasites. This can make antibiotics less effective in the future when a person needs them.

Are there natural antibiotics?

Some natural compounds possess antibacterial and antimicrobial abilities, according to a 2021 review. These might include extracts of bay leaf, black pepper, cumin, garlic, ginger, onion, and turmeric.

Honey and oregano essential oil might also yield antimicrobial properties.

However, the review highlights that many studies on these natural solutions took place in a lab, so their effects on humans are unclear. People need to contact a doctor before trying natural solutions for bacterial infections.

Antibiotics are available in many forms that can treat a wide range of infections. When a person has an allergy to a particular type, or if a bacteria is resistant to an antibiotic, other options can usually treat the infection.

Many antibiotics have a risk of side effects. A person needs to contact a doctor if these become too severe. They may be able to switch the prescription for one that someone can better tolerate. It is important to take antibiotics as a medical professional instructs to reduce the risk of antibiotic resistance.