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Supportive medicines

Allopurinol Before Chemotherapy: — Why You Have Been Given This Tablet

Allopurinol is not a chemotherapy medicine. It is a protective tablet your team has prescribed to prevent a kidney emergency that can occur in the first days of treatment, when large numbers of cancer cells die rapidly.

Medically reviewed by Dr. Naresh Gundu, Medical Oncologist, MBBS (Chalmeda Anand Rao Institute of Medical Sciences, Karimnagar) · DNB Internal Medicine (Sir Gangaram Hospital, New Delhi) · DM Medical Oncology (AIIMS) · Last reviewed September 2026

  • Not a cancer treatment — Allopurinol does not kill cancer cells. It protects your kidneys while chemotherapy does its work.
  • Given before the risk arrives — It is prescribed before treatment begins because preventing the damage is far safer than managing it afterwards.
  • The emergency it prevents has a name — Tumour lysis syndrome can damage the kidneys and disturb the heart rhythm within hours of a first chemotherapy dose.
  • A standard precaution — For patients at risk, allopurinol is part of routine supportive care recommended by major oncology bodies worldwide.
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Allopurinol — sold as Zyloric and other brands — is given before chemotherapy to prevent tumour lysis syndrome. That is a medical emergency that can occur when cancer cells die rapidly and release their contents into the bloodstream, damaging the kidneys. The tablet reduces uric acid, one of the main chemicals responsible for that damage.

What is tumour lysis syndrome and why does it happen?

When chemotherapy works, it kills a large number of cancer cells in a short time. As those cells break down, they release potassium, phosphate, and uric acid into the bloodstream. In patients with many cancer cells, the body cannot clear those chemicals quickly enough.

The result is a sudden chemical imbalance that can damage the kidneys, disturb the heart rhythm, and in severe cases trigger muscle cramps or seizures. It can develop within hours of a first chemotherapy dose, which is why the preventive tablet is started before treatment begins.

Uric acid is one of the main chemicals involved. It forms crystals that can block the tiny filtering tubes inside the kidneys. Allopurinol blocks the enzyme the body uses to produce uric acid, so less is made before it can cause harm.

Who is given allopurinol, and why has it been prescribed for you?

Allopurinol is most often prescribed when a patient has a large number of cancer cells expected to die quickly in response to treatment. It is commonly used in blood cancers — leukaemias, lymphomas, and some aggressive tumours with a high cell burden.

Your oncologist has reviewed your diagnosis, your blood results, and the chemotherapy you are receiving, and decided that prevention is the right step for you. It is not a sign that your cancer is more serious than average — it means your treatment is expected to work quickly, and your team is protecting your kidneys during that window.

If allopurinol is in your prescription bag alongside your chemotherapy medicines, its only job is to protect your kidneys. It is not treating the cancer.

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Which symptoms should you report to your team on the same day during your first treatment cycles?

  • Passing much less urine than usual, or no urine at all
  • Swelling in your legs, ankles, or face
  • Nausea or vomiting that begins in the first few days and does not settle
  • Muscle cramps, twitching, or unusual weakness
  • A fast, fluttering, or irregular heartbeat
  • Feeling confused, unusually drowsy, or very unlike yourself

Did you know?

Some of the most aggressive cancers — Burkitt lymphoma is one example — can shrink dramatically within the first 24 hours of chemotherapy. That speed of response is exactly what makes tumour lysis syndrome the primary safety concern in those first days of treatment.

For patients at risk, preventive treatment with medicines such as allopurinol is now standard supportive care, and it is a large part of why this emergency is rare in settings where prevention is applied.

Source: NCCN Guidelines for Management of Oncologic Emergencies

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Common questions

Frequently asked questions

What is allopurinol called at the pharmacy?

The generic name is allopurinol. In India it is most commonly sold under the brand name Zyloric, and it is also available under various generic brands. Your prescription may show either name — they contain the same active medicine. If the pharmacist offers a substitute brand and you are unsure, check with your care team before accepting it.

Is allopurinol a chemotherapy drug?

No. Allopurinol does not kill cancer cells and plays no role in treating the cancer. It is a supportive medicine whose only job is to prevent a kidney complication that can arise when chemotherapy kills a large number of cells quickly. Think of it as protective equipment for your kidneys, prescribed alongside your treatment, not as part of it.

Why do I take allopurinol before chemotherapy starts, not at the same time?

Tumour lysis syndrome can begin within hours of the first chemotherapy dose, as cells start dying rapidly. Allopurinol needs time to reduce the body's uric acid production before that happens. Starting it in advance means it is already working at the moment of greatest risk. Starting it at the same time as chemotherapy would leave a gap in protection during the most vulnerable window.

Can I stop taking allopurinol if I feel fine?

Please do not stop without speaking to your oncologist or nurse first. Tumour lysis syndrome can develop quickly and without obvious warning — feeling well is the intended result of taking the tablet, not a sign that you no longer need it. Your team will tell you when it is appropriate to stop.

Does allopurinol cause side effects?

Most people tolerate allopurinol without difficulty. A small number of patients develop a skin rash, which should be reported to your team the same day — do not wait for your next appointment, as rashes related to this medicine occasionally need prompt attention. Tell your team about any new rash that appears after you start it, and mention all other medicines, supplements, and herbal or Ayurvedic preparations you are taking, as some combinations need to be monitored.

Will allopurinol affect how well my chemotherapy works?

No. Allopurinol does not interfere with how chemotherapy acts on cancer cells. There is one practical point worth knowing: allopurinol interacts with certain other medicines, and your oncologist will already have checked this when prescribing. If you are started on any new medicine during treatment, remind the prescriber or pharmacist that you are taking allopurinol, so they can confirm there is no interaction.

How common is tumour lysis syndrome?

In patients who receive appropriate preventive care, serious tumour lysis syndrome is uncommon. It was once a significant cause of early treatment-related harm in aggressive blood cancers, before preventive medicines such as allopurinol became standard practice. The fact that your team has prescribed it means they have assessed you as being in the group where prevention is worthwhile — which is exactly the right approach.

What should I tell my team before I start taking allopurinol?

Tell your oncologist or pharmacist about every medicine you are taking — including over-the-counter tablets, vitamins, herbal preparations, and Ayurvedic or traditional medicines. Allopurinol interacts with some other medicines, and your team needs the complete picture to prescribe it safely. Also mention any history of kidney problems and any previous drug allergies or reactions.

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