These widely used medications save countless lives. But they’re not without risks. Learn how (and when) to use antibiotics safely and effectively.
Published June 27, 2022

Table of Contents

  1. What are antibiotics?
  2. Why are there so many types of antibiotics?
  3. How do I take antibiotics?
  4. What are the most common side effects of antibiotics?
  5. Can antibiotics cause more serious reactions?
  6. What are the classes of antibiotics?
  7. What is antibiotic resistance — and why is it a problem?
  8. How do I prevent antibiotic resistance?

In the long history of medicine, few discoveries have been as important as antibiotics. When the first antibiotic became available to the general public in the 1940s, it was literally a lifesaver. Doctors could now treat infectious diseases, such as pneumonia, which was the leading cause of death in the early 1900s in the U.S. And it made many modern medical treatments possible, including open-heart surgery.

Since then, more than 100 antibiotics have been approved by the U.S. Food and Drug Administration (FDA). These powerful medications treat everything from urinary tract infections to acne. (If you need an antibiotic, show the Optum Perks prescription discount card to your pharmacist to see how much you could save.)

As with all medications, antibiotics can have side effects. And they can treat only certain kinds of conditions. Read on for expert insight on how to get the most out of your antibiotic treatment.

What are antibiotics?

These medications fight bacterial infections. Some antibiotics work by killing the harmful bacteria outright. Others interfere with the bacteria’s ability to grow and multiply. Examples of bacterial infections that can be treated with antibiotics include:

  • Bacterial conjunctivitis (pinkeye)
  • Bladder infections
  • Strep throat
  • Whooping cough
  • Severe acne
  • E. coli infections

Antibiotics don’t work against infections caused by viruses. Common examples are the common cold, COVID-19 or the flu. And not all bacterial infections need antibiotics, according to the Centers for Disease Control and Prevention (CDC). Some, such as sinus infections, may get better on their own.

Why are there so many types of antibiotics?

Some antibiotics work only against specific bacteria. Plus, the bacteria they’re trying to fight constantly mutate and adapt. The more the bacteria are exposed to a certain antibiotic and live, the more they evolve to resist it. So different antibiotics may need to be used to help fight the infection.

“Antibiotic resistance is a serious concern,” says Nathan Shankar, PhD. He’s a professor and vice chair of the department of pharmaceutical sciences for the College of Pharmacy at the University of Oklahoma Health Sciences Center in Oklahoma City. “We could end up facing a scenario where none of the antibiotics in use today would be effective in treating serious infections.”

That’s why it’s important to take an antibiotic only when you really need it. Just as important: Take it exactly as prescribed.

How do I take antibiotics?

Antibiotics come in several forms. Some, such as tablets or liquids, you take by mouth. Others you apply to your skin, such as creams or ointments. And some are delivered by injection or IV.

No matter what kind you’re prescribed, it’s critical to follow the directions exactly. That means taking your medication for as long as your doctor tells you to. Here’s why: Those wily bacteria learn each time they go up against an antibiotic. If you don’t stop them completely, they can bounce back and become resistant to the antibiotic you were taking.

“You want to make sure to kill the bacteria so they don’t have a chance to multiply and mutate,” says Ashley Garling, PharmD. She’s a clinical assistant professor for the College of Pharmacy at the University of Texas at Austin.

It’s also important to take antibiotics at the right time of day. Some are meant to be taken twice a day. That usually means once in the morning and once at night, not 2 at the same time, Garling says. The idea is to have a steady stream of the medication in your bloodstream at all times. This helps keep the bacteria under control, she adds.

Garling also recommends taking an antibiotic after a meal to help avoid stomach upset. But be sure to read your prescription carefully. Some antibiotics may need to be taken on an empty stomach.

What are the most common side effects of antibiotics?

A study published in JAMA Internal Medicine found that about 20% of people in a hospital setting experienced some kind of side effect from taking an antibiotic. By far, the most common one is stomach upset, Garling says. That can include:

  • Diarrhea
  • Nausea
  • Stomach cramping
  • Vomiting

In many cases, you can help prevent an upset stomach by taking your antibiotic after or with a meal, says Steven Leonard, PharmD. He’s an associate professor of pharmacy practice at the Raabe College of Pharmacy at Ohio Northern University in Ada.

Antibiotics can also cause yeast infections, most often in the throat and vagina. A yeast infection in the throat or mouth is called thrush. These infections are caused by a type of yeast (the candida fungus) that already exists in your body. And it usually doesn’t cause many problems. But when an antibiotic wipes out other bacteria in those areas, the candida fungus can grow out of control. It can be treated by taking an antifungal medication.

Can antibiotics cause more serious reactions?

Antibiotics are not without risks, especially when overused. But, Leonard says, “in general, they are pretty safe compared to many other drugs out there.”

In rare instances, though, antibiotics can cause more serious side effects, such as:

  • Allergic reactions: They account for nearly 4 out of 5 antibiotic-related emergency department visits. These reactions can include rashes, breathing problems and swelling of the face and throat, according to the Cleveland Clinic.
  • C. difficile infection: An antibiotic doesn’t kill just the bad bacteria in your body. It can also wipe out the good bacteria in your gut. That good bacteria help keep certain troublemakers, such as C. difficile (C. diff) in check. And when the good bacteria are gone, the harmful ones can grow out of control and make you sick.

Symptoms of a C. diff infection can include severe diarrhea, belly cramping, weight loss, nausea and loss of appetite. Older adults are especially at risk. C. diff is usually treated by taking another antibiotic paired with a probiotic. The probiotic encourages more good bacteria to grow and prevents the C. diff from coming back.

What are the classes of antibiotics?

Antibiotics that share a chemical structure are grouped into classes. There are more than a dozen classes. Your doctor chooses the one that’s right for you, depending on lots of different factors.

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Some antibiotics are known as narrow spectrum. They work against just a few types of bacteria. Others are broad spectrum. This means they “are effective against a lot of different types of bacteria,” Leonard says. When appropriate, it’s better to take a narrow-spectrum antibiotic. That means you expose fewer types of bacteria to an antibiotic.

Here are some of the common classes of antibiotics and the possible reasons your doctor might prescribe them:

Class: Cephalosporins
Examples: Cephalexin (Keflex®), cefdinir, cefuroxime
Used for: Pneumonia as well as infections of the skin, ears, sinuses, chest, throat, tonsils and urinary tract
How they work: They prevent formation of the bacteria’s cell wall.

Class: Fluoroquinolones
Examples: Ciprofloxacin (Ciloxan®), levofloxacin, moxifloxacin (Vigamox®, Moxeza®)
Used for: Pneumonia as well as skin, bone, kidney, sinus, respiratory and prostate infections (Ophthalmic formulations target bacterial conjunctivitis.)
How they work: They prevent the bacteria from making new DNA.

Class: Lincosamides
Example: Clindamycin (Cleocin®)
Used for: Joint, bone, abdomen, teeth and vaginal infections
How they work: They prevent bacteria from making proteins that allow them to multiply.

Class: Macrolides
Examples: Azithromycin (Zithromax®), clarithromycin, erythromycin
Used for: Certain pneumonias, plus sinusitis, tonsillitis, chlamydia and syphilis
How they work: They prevent bacteria from making proteins that allow them to multiply.

Class: Penicillins
Examples: Amoxicillin, penicillin
Used for: Pneumonia and infections of the ear, nose, throat, chest, urinary tract, respiratory tract and skin
How they work: They prevent the formation of the bacteria’s cell wall.

Class: Tetracyclines
Examples: Doxycycline (Targadox®, Doryx®), tetracycline
Used for: Chest and mouth infections, and some sexually transmitted infections. They can also be used for acne and rosacea, Lyme disease and malaria prevention.
How they work: They prevent bacteria from making proteins that allow them to multiply.

Class: Urinary anti-infectives
Examples: Methenamine (Hiprex®), nitrofurantoin (Macrobid®)
Used for: Urinary tract infections (UTIs)
How they work: Some kill the bacteria directly, while others prevent the bacteria from multiplying.

What is antibiotic resistance — and why is it a problem?

Many people take an antibiotic when they really don’t need to. In some cases, their infection isn’t caused by bacteria. In others, the infection would have cleared on its own. The CDC estimates that 47 million antibiotic prescriptions are written every year for these exact reasons.

Then why are antibiotics prescribed if they won’t help? It’s often because patients expect them. “There’s a lot of pressure on physicians to prescribe an antibiotic,” Garling says.

And the more an antibiotic is prescribed, the more the chance that the bacteria will become resistant to it. Plus, bacteria that aren’t fully killed by an antibiotic can learn how to evade that medication in the future. And that’s a huge problem. Every year, there are about 2.8 million antibiotic-resistant infections in the U.S., according to the CDC. And of those, 35,000 people die as a result.

How do I prevent antibiotic resistance?

The only way to avoid antibiotic resistance completely is to not use antibiotics, Leonard says. But that isn’t always a realistic option. Antibiotics are vital to preventing and treating so many conditions. And they save countless lives every year.

So what can you do? Cut down on their unnecessary use. “We can use antibiotics better to try to slow or minimize the development of resistance,” Leonard advises.

Antibiotics aren’t always the answer when you’re sick, says the CDC. So talk with your doctor about the best treatment for your illness. These steps can help you stay at your healthiest:

  • Take antibiotics only when necessary. “If you’re a healthy individual, you might want to watch and wait and not get on an antibiotic unless you can’t recover naturally or you’re getting worse,” Garling says. That doesn’t mean you should ignore an illness or not go to the doctor. (If you have diabetes or heart or lung problems, she adds, your risk of developing a more serious infection is higher. So seeing your provider is especially important.)
  • Take your antibiotics as prescribed. Not taking the full course of your prescription could allow some of the bacteria to live. And this might give them a chance to resist that antibiotic going forward.
  • Keep up with your vaccinations. Getting the shots you need can help lessen your chance of getting sick and needing an antibiotic. That’s especially true for bacterial infections such as whooping cough and pneumonia.
  • Prevent the spread of germs. Stop germs in their tracks to prevent infections. Here’s how: Wash your hands regularly and stay home when you’re sick.

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Additional sources
Infections that can be treated with antibiotics: Centers for Disease Control and Prevention
Study on the prevalence of antibiotic side effects: JAMA Internal Medicine (2017). “Association of adverse events with antibiotic use in hospitalized patients”
Serious adverse reactions from antibiotics: Cleveland Clinic
About antibiotic resistance: Centers for Disease Control and Prevention