Should I take medicine for a fever during chemotherapy?

Talk with your doctor or nurse before taking any medicine—even aspirin, acetaminophen (such as Tylenol), or ibuprofen (such as Advil)—for a fever during cancer treatment.

These medicines can lower a fever, but they may also mask or hide the signs of a more serious problem. Because infections during treatment can be life threatening, your team needs to know about a fever before it is treated.

Here is why hiding it is the danger. During much of chemotherapy, a fever is not a symptom to be managed. It is a signal. Chemo lowers the number of neutrophils, the white blood cells that fight bacteria. That state is called neutropenia, and it is defined as fewer than 1,500 neutrophils per microliter of blood. With few neutrophils on duty, an ordinary infection can move fast, which is why the National Cancer Institute calls infection during cancer treatment a reason for urgent medical attention.

Acetaminophen will bring the number on the thermometer down. It does nothing to the bacteria. If the fever drops and you decide not to call, you may lose the only warning you were going to get, at the exact hours when antibiotics would have done the most good.

There is a second reason to ask first. Many over-the-counter medicines contain aspirin or ibuprofen, which can raise your risk of bleeding. Chemotherapy can also lower platelets, the cells that help blood clot. Taking a bleeding-risk drug during a low platelet stretch is a bad combination, and cold and flu products often contain these ingredients without saying so on the front of the box.

Call your health care team if you have a fever of 100.4–100.5°F (38°C) or higher, and follow their instructions about what to do next. Sources word this threshold slightly differently, so use the number your own team gave you. Inside hospitals, the formal definition of febrile neutropenia is a single oral temperature of 101°F (38.3°C) or higher, or 100.4°F (38°C) or higher lasting at least an hour, in someone with a low neutrophil count.

Do this in order. Take your temperature first, before any medicine. Write down the number and the time. Then call, even at night, even on a weekend. Let the team decide whether to treat the fever. If they say yes, they will tell you which medicine and how much.

Fever is not the only thing worth calling about. NCI also lists chills, cough or sore throat, diarrhea, ear pain, headache or sinus pain, a stiff or sore neck, skin rash, sores or a white coating in the mouth, swelling or redness where a catheter enters the body, and urine that is bloody, cloudy, or painful to pass. Report these even if your temperature reads normal.

Two things are worth setting up before you need them: a working thermometer within reach of your bed, and the after-hours phone number saved in your phone. Both are easy to arrange on a good day and nearly impossible to sort out at 2am.