Which Antibiotics Can Cause Diarrhea?

Some antibiotics may cause loose stools or even another infection

United Kingdom - London - Medication pill bottles
Antibiotics have dramatically changed healthcare but they can sometimes come with a price, which is why their responsible use is so important. Image © Corbis via Getty Images / Getty Images

Antibiotics are lifesaving for many people who have bacterial infections. However, antibiotics can have some unintended negative effects, including diarrhea, which can be severe. This article describes the ins and outs of antibiotic-associated diarrhea.

Why Antibiotics Cause Diarrhea

The first thing to understand is that there are many types of bacteria in our bodies, some of which never cause disease and others that can cause disease sometimes. For the most part, bacteria tend to live in harmony within the intestines and in other surfaces on the body. When antibiotics are introduced into the body, the balance of the bacteria is altered. That alteration changes the way the intestine handles nutrients and fluids and changes its motility. When that happens many people develop some diarrhea.

Clostridium difficile: One Type Of Bad Bacteria

We need the beneficial bacteria in our digestive tract, but that doesn't mean that all the bacteria that lives there is doing good work for our bodies. There is also harmful bacteria living in the digestive tract. Most of the time, the good strains of bacteria can overtake the harmful strains, keeping the bad stuff in check and preventing it from causing disease.

In small amount of people (2% to 3%), a bacteria called Clostridium difficile lives in the colon. In a minority of those people, C difficile may begin to multiply and take over the colon after taking a course of antibiotics. This can unfortunately result in C difficile-associated diarrhea (also called pseudomembranous colitis). This disease causes diarrhea and in rare cases may also be associated with toxic megacolon, a life-threatening surgical emergency.

The Antibiotics That Can Cause Complications

Any antibiotic can disrupt the flora in the large intestine and lead to bacteria die-off there. However, not every type of antibiotic carries the same amount of likelihood of contributing to C difficile colitis. While it's true that taking any antibiotic can result in C difficile colitis, there are some antibiotics that have a higher risk of doing so than others.

The antibiotics most responsible for C difficile colitis are the ones that are formulated to kill a wide variety of bacteria, which makes sense, because they are going to have an effect on the most different types of bacteria, including the good ones. The antibiotics most associated with C difficile colitis are:

  • Cephalosporins
  • Clindamycin
  • Fluoroquinolones
  • Penicillins

The antibiotics that carry a moderate amount of risk include:

  • Imipenem
  • Macrolides
  • Sulfa-trimethoprim 

Those antibiotics with the lowest risk are:

  • Aminoglycosides
  • Metronidazole
  • Nitrofurantoin

The Role of Probiotics in Preventing Diarrhea

Probiotics are widely available in supermarkets and drug stores but they're not all created equally. They may contain different strains of bacteria and different amounts, and they're largely unregulated, though there are some brands that are more reliable than others. What's more, it's not been determined which ones may help, or even how much of them should be taken. Therefore, there's no blanket recommendation about taking probiotics after a course of antibiotics. It's suggested that sometimes a probiotic may help, but it's not going to be true in all cases, and the cost of probiotics and the potential harm they can cause must also be considered.

For people who have inflammatory bowel disease (IBD), especially those with an ostomy or a j-pouch, it is important to talk to a gastroenterologist about antibiotics. Antibiotics have been associated with IBD flare-ups, and a gastroenterologist may have suggestions about whether a probiotic would be helpful, and which brand to use. 

A Word From Verywell

A bacterial infection may need to be treated with antibiotics, and there may be no way of getting around it. The choice of antibiotics used won't be based on whether or not it has a low risk of C difficile colitis, but rather on what is the right choice for killing the bacteria that's causing the infection.

If you have concerns about having problems with diarrhea after taking antibiotics, talk to your physician. In some cases, there way be some leeway with which antibiotic to use, but it has to be effective against the bacteria that is causing the infection. Taking probiotics may be an option to repopulate the colon with good bacteria, but that should be discussed with a physician, because again, the right ones need to be chosen.

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