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A guide to the most common antibiotics

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Common antibiotics Side effectsWhich one to takeSummary
Antibiotics are medications used to treat and prevent bacterial infections. There are hundreds of antibiotics, but the most common ones include amoxicillin, doxycycline, and erythromycin.
Medically reviewed by Monica Kean, PharmD
Written by Suan Pineda
Updated on November 8, 2023

Antibiotics are medications used to treat or prevent infections caused by bacteria, such as urinary tract infections (UTIs), strep throat, and ear infections. 

Bacteria or viruses can cause infections. Antibiotics can kill bacteria and some parasites, but not viruses. Antibiotics can’t treat the common cold or the flu.

Hundreds of antibiotics treat different types of illnesses caused by bacteria. But some are more common than others and treat different common infections.

Common antibiotics 

A close up of a person's mouth as they take one of the most common antibiotics
Studio Firma/Stocksy United

Six of the most common groups of antibiotics include:

  • penicillins
  • cephalosporins
  • aminoglycosides
  • tetracyclines
  • macrolides
  • fluoroquinolones

Healthcare professionals gave 211.1 million antibiotic prescriptions in 2021, according to the Centers for Disease Control and Prevention (CDC). Amoxicillin was the most commonly prescribed antibiotic, making up 22.6% of all antibiotic prescriptions, according to data from Definitive Healthcare.

Amoxicillin

Amoxicillin (Amoxil) is a type of penicillin used to treat certain infections such as pneumonia and bronchitis. It also treats infections of the ears, nose, throat, urinary tract, and skin.

Amoxicillin comes in tablet or liquid form or as an injection, usually given in a healthcare setting like a doctor’s office.

Brand names: Amoxil, Amoxil Pediatric Drops, Dispermox, Larotid Suspension, Moxtag, Polymox Suspension, Trimox, Trimox Pediatric Drops, Wymox.

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Doxycycline

Doxycycline (Adoxa) is a type of tetracycline. Doxycycline is an antibiotic with anti-inflammatory properties used to treat a variety of bacterial infections, from skin conditions to pelvic and urethral infections. Doxycycline also treats and prevents anthrax.

Doxycycline comes in tablet and liquid form.

Brand names: Acticlate, Acticlate CAP, Adoxa, Doryx, Doryx MPC, Doxychel, Monodox, Oracea, Periostat, Vibra-Tabs, Vibramycin.

Erythromycin

Erythromycin (Erythrocin) is a type of macrolide. Erythromycin can treat infections such as bronchitis, pneumonia, Legionnaires disease, whooping cough, and diphtheria. It can also treat some sexually transmitted infections (STIs) like syphilis.

People with an allergy to penicillin can take erythromycin to treat certain bacterial infections.

Brand names: EES, ERY-C, Ery-Tab, Erythrocin, PCE, Pediamycin.

Cephalexin

Cephalexin (Keflex) is a type of cephalosporin used to treat a range of conditions, from respiratory tract infections such as pneumonia to UTIs, pelvic infections, and gonorrhea.

People allergic to penicillin could take specific cephalosporins, such as cefuroxime (Zinacef) and ceftriaxone (Rocephin), to treat certain bacterial infections. Others may cause allergic reactions.

Cephalexin comes as a tablet or in liquid form.

Brand names: Keflet tablets, Keflex, Keftab tablets, Panixine disperdose.

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Ciprofloxacin

Ciprofloxacin (Cipro) is a type of fluoroquinolone. It treats pneumonia, gonorrhea, typhoid fever, and infections of the bones, skin, joints, ears, and eyes. 

Ciprofloxacin comes in tablet and liquid form.

Brand names: Cipro oral suspension, Cipro tablets, Cipro XR tablets, Proquin XR tablets.

Sulfamethoxazole and trimethoprim

Sulfamethoxazole trimethoprim (Bactrim) is a type of sulfonamide, also known as co-trimoxazole. Sulfamethoxazole trimethoprim treats pneumonia, bronchitis, UTIs, and infections of the ears and intestines.  

Sulfamethoxazole trimethoprim comes in tablet and liquid form.

Brand names: Bactrim, Bactrim DS, Septra, Septra DS, Septra suspension, Sulfatrim suspension.

Nitrofurantoin

Nitrofurantoin (Macrobid) is an antibiotic commonly prescribed to treat UTIs.

It comes in capsule or liquid form.

Brand names: Furadantin tablets, Furadantin oral suspension, Furalan, Macrobid, Macrodantin.

Side effects of antibiotics

Antibiotics can cause side effects such as:

  • diarrhea
  • feeling sick
  • allergic reactions that include:
    • raised, itchy skin rash
    • coughing
    • wheezing
    • tightness of the throat

Some more serious side effects include:

  • sensitivity to light
  • aches
  • heart palpitations
  • shortness of breath
  • kidney failure
  • seizures

If you experience any of these serious adverse effects while taking antibiotics, go to your nearest emergency service and contact a healthcare professional. 

Also, taking antibiotics regularly can lead to antibiotic resistance. The CDC recommends that you take antibiotics only when needed to make sure they stay as effective as possible. 

How to decide which one to use

A healthcare professional prescribes antibiotics.

The specific type of antibiotics to take depends on which bacterial infection you have. Talk with a healthcare professional if you have symptoms of an infection. They can help determine whether a bacteria or a virus causes the infection.

If it’s a bacterial infection, they’ll determine the type of bacteria and what’s the best antibiotic to treat your infection. 

It’s important that you take the full course of the prescribed antibiotic — that is, continue taking it even when your symptoms disappear until you finish your course of antibiotics. 

Summary

Antibiotics are medications used to treat bacterial infections. Sometimes, antibiotics treat kill parasites.

There are hundreds of antibiotics, but some common ones treat bacterial infections such as pneumonia, bronchitis, UTIs, and STIs. These include amoxicillin, erythromycin, and co-trimoxazole.

A healthcare professional prescribes antibiotics. The CDC recommends taking antibiotics only when needed to prevent antibiotic resistance. 

Antibiotics can cause side effects such as diarrhea, feeling sick, and shortness of breath. If you’re experiencing any of these adverse effects, contact a healthcare professional.

Download the free Optum Perks Discount Card to save up to 80% on some prescription medications.

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