Antibiotics and Antifungals — During Chemotherapy

Not to everyone. They are prescribed when your regimen is likely to bring your white blood cell count low enough to significantly increase infection risk, or when a specific infection risk applies to your treatment. Regimens for blood cancers and those used around bone marrow transplants commonly include prophylaxis. Many solid tumour regimens do not. Your oncologist will explain whether your treatment requires it.

Cotrimoxazole — sold as Septran or Bactrim — protects against Pneumocystis jirovecii pneumonia, a lung infection that is uncommon in healthy people but can become life-threatening when the immune system is suppressed. It is one of the most commonly prescribed preventive antibiotics in oncology. Your team will tell you whether it applies to your regimen.

For the same reason an antibiotic is given before a bacterial infection — to stop one from starting. When your white blood cell count is very low, fungi that normally live harmlessly on your skin or in your gut can enter the bloodstream and become dangerous. Fluconazole (Zocon, Forcan) and itraconazole (Canditral) are the most commonly prescribed antifungals for this purpose. Posaconazole (Noxafil) may be used for higher-risk regimens.

No. Leftover antibiotics from a previous illness are not the right treatment for infection during chemotherapy, and taking them creates two serious problems. They are unlikely to cover the organisms that threaten someone with low white cells. And they can reduce a fever and mask the warning sign your team most needs to act on. A fever during chemotherapy means call your team or go to hospital — not treat at home.

Call your oncology team immediately or go to your nearest emergency department. Preventive antibiotics reduce the risk of infection; they do not eliminate it. A fever on top of prophylaxis means the preventive medicine was not enough, and you need assessment, blood tests, and blood cultures without delay. Do not assume the fever will settle because you are already taking an antibiotic.

No. They protect against a specific set of infections your team judged you were most at risk from — not all bacteria, all fungi, or any viruses. Good hand hygiene, avoiding contact with people who are unwell, and reporting a fever promptly are still essential, even when you are on prophylaxis.

Tell them before any tests or blood cultures are taken — ideally at the start of your assessment. Which medicines you took, when, and for how long all matter. This will not get you into trouble; your team needs the information to make the right decisions. If you feel unwell or have a fever, go in rather than waiting to mention it at your next scheduled appointment.

If you develop a fever or signs of active infection during chemotherapy, your team may start a treatment-level antibiotic while waiting for blood culture results to identify the cause. The medicines used for treatment are often different from the ones used for prevention, and the choice depends on the culture results, locally common organisms, and your previous antibiotic history. Your team will adjust as the picture becomes clearer.