When should I take antibiotics? 7 questions, answered

Antibiotics are a class of medications used to treat bacterial infections. They work by either killing the bacteria outright or by disabling them so that they can’t grow or reproduce.

But antibiotics, like all medications, can sometimes produce side effects. So, are there any situations in which someone absolutely should — or should not — take antibiotics? And, are there any special rules about antibiotics for cancer patients?

We went to Natalie Dailey Garnes, M.D., head of our antimicrobial stewardship program, for advice. Here’s what she shared.

How many different kinds of antibiotics are there?

Dozens. But each one is only useful against particular kinds of bacteria. Broad-spectrum antibiotics will kill more than those classified as narrow-spectrum, but even narrow-spectrum antibiotics will usually still affect several different types.

How do doctors decide which antibiotics to use? 

Normally, that’s determined by what the bacteria look like. So, we’ll take a sample of whatever it is we’re culturing — whether that’s urine or mucus someone coughed up — then stain it with two different types of dye and look at it under a microscope. 

The reason for this is that bacteria are often divided into two main groups: Gram positive and Gram negative. The designation is based on how the cell walls are structured. And some antibiotics work against one group but not the other.

Doctors don’t always have something available to culture, though. If someone has an abscess located deep inside their abdomen, for instance, the only way to obtain a sample of it might be to perform an invasive procedure. And, if the risks of doing that procedure outweigh the benefits, then doctors might make an educated guess based on the infection’s location and pick an antibiotic based on that instead. That’s because certain bacteria are more likely to be found in certain parts of the body.

E. coli, for example, is usually associated with both urinary tract infections and the gastrointestinal tract. So, if a doctor isn’t sure exactly what something is yet in one of those areas, but they need to act fast, the combination of antibiotics they pick will likely cover that bacteria.

If antibiotics are so great, why shouldn’t we just take them all the time?

Every medicine has potential side effects. And when you take an antibiotic, it’s not just killing off the bad bacteria you’re targeting. It’s killing off some of the good bacteria, too. That can allow other things that might be lurking around to grow. This could include yeast or other, unaffected bad bacteria. And if they don’t have to fight as hard for resources thanks to the antibiotic, you could end up with another infection, which you definitely don’t want.

Equally important, though, is the figure I cited earlier. Right now, we only have dozens — not hundreds — of antibiotics available. And as more bacteria get exposed to these drugs, they can develop resistance and become superbugs.

That means patients and their doctors might have fewer options in the future. So, we don’t want people to take antibiotics when they don’t need them. Otherwise, they might not be available when they actually do.

When do cancer patients really need to take antibiotics?

We’ll often give antibiotics to cancer patients whose neutrophil counts are really low. This can help prevent infections. We’ll also give them to cancer patients who are receiving certain types of chemotherapy, since their cancer treatment puts them at greater risk of developing specific types of infection. 

It’s really important for those patients to take their antibiotics exactly as prescribed.  

Are there any situations when cancer patients should not take antibiotics?

Yes. As we’re coming to understand the gut microbiome better, we’re learning that the normal flora found in and around the gut can actually help people with certain types of cancer respond better to their treatment, particularly immunotherapy. So, taking antibiotics when you don’t need them could actually prevent therapies from working as well as they otherwise would.

Antibiotics may also interact with experimental therapies. So, if you’re receiving one of those through a clinical trial, you need to clear it with your study coordinator before taking any antibiotics prescribed by an outside physician.

Why is it important to take antibiotics exactly as prescribed?

Sometimes, you may start to feel better even before an infection has completely resolved. But if you stop taking the antibiotics at that point, the infection could still come back. And nobody wants that.

What’s the most important thing for people to remember about antibiotics?

Just because you’re sick doesn’t necessarily mean that you need an antibiotic. Antibiotics only work against bacteria, so if you have a viral infection, they will not be effective at all. 

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