Oral thrush: Prevention during cancer treatment

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Some antimycotic (antifungal) drugs can prevent oral thrush from developing during cancer treatment with chemotherapy or radiotherapy. But topical medications, which only work locally in the mouth, haven’t been scientifically proven to prevent oral thrush.

Candida is a type of yeast (fungus) that lives in the gastrointestinal tract. Most people have it in their mouth and throat, where is usually doesn't cause any problems. But certain conditions, such as a weakened immune system, allow the yeast to grow a lot more. The symptoms of oral thrush (oral candidiasis) include a white coating and inflamed areas in the mouth and throat.

Oral thrush is a common side effect of cancer treatments. These treatments damage the body's mucous membranes and weaken the immune system. This makes it more difficult for the body to fight off the Candida infection. The risk of developing oral thrush depends on the type of cancer and the intensity of treatment.

Medications for preventing oral thrush

Fungal infections on the tongue and on the membranes lining the mouth can be treated with various types of antimycotic (antifungal) drugs. But it may be difficult to get rid of the infection completely while having cancer treatment. This makes it even more important to try to prevent an infection in the first place.

One option is to already start taking antimycotic drugs during cancer treatment as a precaution. Some of these medications are available in the form of mouthwashes, gels or ointments. Others are taken in the form of lozenges, capsules or tablets, or given as an infusion.

Which antimycotics are effective against oral thrush?

Researchers from the Cochrane Collaboration analyzed 28 studies to find an answer to this question. The studies looked into whether antimycotics can successfully prevent oral thrush when used during chemotherapy or radiotherapy for cancer treatment.

They involved a total of more than 4,200 cancer patients, most of them adults. The participants had different types of cancer, but leukemia was the most common.

Antimycotics work in different ways. How a particular antimycotic is absorbed by the body will depend on the dosage form and the specific drug. There are

  • medications that have an effect on a limited, local region (topical medications),
  • medications that have an effect on the entire body (systemic medications), and
  • medications that do both.

Antimycotic drugs that have a local effect

Topical antimycotics are applied directly to the parts of the mouth that are at risk – for example in the form of an ointment or gel – or they might be used in the form of a fluid to rinse out the mouth. When applied topically like this, the drugs don't enter the body through the digestive tract. In the studies, topical antimycotics weren’t found to prevent oral thrush during cancer treatment.

Antimycotic drugs that affect the whole body

Drugs that have an effect on the entire body (systemic treatment) can enter the bloodstream through the digestive tract. They are available in various forms, such as capsules or tablets. The studies showed that these types of antimycotic drugs can lower the risk of oral thrush during cancer treatment:

  • 28 out of 100 participants who took only a placebo (fake treatment) developed oral thrush, compared with
  • 13 out of 100 participants who took an antimycotic drug with a systemic effect.

Antimycotic drugs with a combined effect

Antimycotics that have an effect both in the mouth and in the rest of the body also lowered the average risk of developing oral thrush:

  • Oral thrush developed in about 56 out of 100 participants who took a placebo or didn’t take any preventive medication, compared to
  • around 9 out of 100 participants who took an antimycotic with a combined effect (systemic and topical).

The results were similar for adults and for children.

Side effects were recorded in 13 of the 28 studies. Up to 18 out of 100 study participants experienced side effects. The most common side effects of antimycotics were headaches, skin rashes, nausea, vomiting and diarrhea.

Unfortunately, the studies provided very little information about whether the antimycotic drugs helped reduce oral thrush symptoms such as pain or difficulties swallowing. It’s also still not clear whether these drugs can shorten hospital stays or influence quality of life. And the 28 studies didn’t properly examine the issue of whether antimycotic drugs can help to prevent an oral thrush infection from spreading to the rest of your body.