Types of Antibiotics

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  • The discovery of the first true antibiotic—penicillin—in 1928 was one of the most life-changing events of the 20th century. Before its discovery, when bacterial infections developed, there wasn’t much doctors could do. People died from illnesses and injuries that are highly curable today. Now, there are more than 100 antibiotics to fight the war against bacterial infections. Here is a look at common antibiotic names and the types of antibiotics your doctor may prescribe.

  • 1
    Penicillins
    Close-up of penicillin prescription bottle label

    The first penicillin gave rise to an entire class of antibiotics known as penicillins. Penicillins are derived from a specific mold (a type of fungi)—Penicillium. They are widely useful antibiotics that are often a doctor’s first choice for several types of infections. This includes skin, respiratory, ear, STDs (sexually transmitted diseases), and dental infections. They are highly effective against familiar organisms, such as staph and strep. Rashes and allergic reactions are common with penicillins. Other common side effects include diarrhea, nausea, and abdominal pain. Examples of penicillins include:

    • Amoxicillin

    • Ampicillin

    • Penicillin G

    • Penicillin V

  • 2
    Cephalosporins
    Red and white capsules in blister pack

    Cephalosporins are related to penicillins. They both belong to a larger class called beta lactams. Like penicillins, cephalosporins originally came from a fungus—Cephalosporium. There are five generations of cephalosporins. Each generation covers different types of bacteria. As a result, the class can treat a variety of infections, from strep throat and skin infections to very serious infections like meningitis. Because they are related to penicillins, some people with penicillin allergies may also react to cephalosporins. Other common side effects include diarrhea, nausea, heartburn, and abdominal pain. Examples of cephalosporins include:

    • Cefixime

    • Cefpodoxime

    • Cefuroxime

    • Cephalexin

  • 3
    Macrolides
    Z-pak antiobiotics in blister pack

    Macrolides are a completely different class of antibiotics from the beta lactams. But they effectively treat many of the same infections. This includes respiratory, ear, skin, and sexually transmitted infections. So, they are very useful for people with allergies to beta lactams. They are also useful when bacteria develop resistance to beta-lactam antibiotics. However, macrolides have a lot of drug interactions. Be sure your doctor and pharmacist know about all your medications when you take a macrolide. Common side effects include nausea, vomiting, stomach pain, and diarrhea. Examples of macrolides include:

    • Azithromycin (‘Z-pak’)

    • Clarithromycin

    • Erythromycin

  • 4
    Fluoroquinolones (broad-spectrum antibiotics)
    Close-up of Ciprofloxacin antibiotic in blister pack

    Fluoroquinolones—or quinolones—are active against a very wide variety of bacteria. This makes them useful for treating infections when other antibiotics have failed. They are also an alternative when people have allergies to other antibiotics. They can treat anything from eye infections to pneumonia to skin, sinus, joint, urinary or gynecologic infections and many more. However, this class can be a problem for people with certain heart conditions and with some other medicines. Be sure your doctor and pharmacist know your complete medical history. Common side effects include stomach upset or pain, diarrhea, headache and drowsiness. Examples of fluoroquinolones include:

    • Ciprofloxacin

    • Levofloxacin

    • Moxifloxacin

  • 5
    Sulfonamides
    Red and yellow capsules spilling out of white pill bottle

    Derived from the chemical sulfanilamide, ‘sulfa drugs’ have been around about as long as penicillin. Technically, sulfonamides don’t kill bacteria the way other antibiotics do. Instead, they are bacteriostatic—they stop bacterial growth and your immune system does the rest. They are very good topical treatments for burns and vaginal or eye infections. They can also treat UTIs (urinary tract infections) and traveler’s diarrhea. However, resistance is common with this class. Common side effects include diarrhea, nausea, rash, and sun sensitivity. Allergies are also common with the group. Examples of sulfonamides include:

    • Sulfacetamide

    • Sulfadiazine

    • Sulfamethoxazole-Trimethoprim

  • 6
    Tetracycline
    Close-up of two red and yellow pill capsules

    These antibiotics come from a species of bacteria called Streptomyces. It seems odd that a bacterium could produce an antibiotic that kills other bacteria, but it’s true. Tetracyclines are bacteriostatic, like the sulfonamides. They treat various infections, such as respiratory, skin and genital infections. They also treat unusual infections, including Lyme disease, malaria, anthrax, cholera, and plague. They have noninfectious uses as well, such as treating rosacea. Common side effects include stomach pain or upset, sun sensitivity, and yeast infections. Examples of tetracyclines include:

    • Doxycycline

    • Minocycline

    • Tetracycline

  • 7
    Other Types of Antibiotics
    Overhead view of man with pill in one hand and cup of tea in the other

    Doctors have several other antibiotic choices if none of these classes will work. You will find some of them only in a hospital. Others just don’t fit into the main groups, but are very useful. This includes antibiotics like clindamycin, metronidazole (Flagyl) and nitrofurantoin (Furadantin, Macrodantin). Each antibiotic, whether in a defined class or not, has different dosing requirements. You need to take some on an empty stomach and others with food. Ask your doctor or pharmacist about the best way to take an antibiotic. With all antibiotics, it’s important to finish the entire course your doctor prescribes. This ensures adequate treatment and prevents antibiotic resistance.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Apr 27
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Bacteria and Antibacterial Drugs. Merck Manual Professional Version. https://www.merckmanuals.com/professional/infectious-diseases/bacteria-and-antibacterial-drugs
  2. Discovery and Development of Penicillin. American Chemical Society. https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/flemingpenicillin.html
  3. Drugs, Herbs and Supplements. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/druginformation.html
  4. Sulfanilamide. American Chemical Society. https://www.acs.org/content/acs/en/molecule-of-the-week/archive/s/sulfanilamide.html
  5. Tetracycline. American Chemical Society. https://www.acs.org/content/acs/en/molecule-of-the-week/archive/t/tetracycline.html