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Mercaptopurine dosing in childhood leukaemia maintenance | CION Cancer Clinics
Mercaptopurine is the daily tablet at the heart of maintenance treatment for childhood acute lymphoblastic leukaemia. Its dose is not fixed. It starts from a level set by your child's TPMT and NUDT15 gene results, then moves up or down with regular blood counts for the whole of maintenance. This page explains how that dosing works, what parents do at home, and which warning sign cannot wait. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- How is the mercaptopurine dose decided during maintenance?
- Which medicines make up a typical maintenance plan?
- What does a month of maintenance look like at home?
- The words you will hear in maintenance clinic
- What this page cannot tell you
- Four things parents believe about maintenance tablets
- Common questions about maintenance dosing
The short answer
How is the mercaptopurine dose decided during maintenance?
The oncologist starts from a standard dose worked out from your child's body size, and lowers it if the TPMT or NUDT15 gene tests show the body clears the drug slowly. After that, blood counts steer it. The aim is a white cell count in a target range: low enough to show the drug is working, but not so low that infections take hold.
Why maintenance lasts so long
Maintenance is the longest phase of treatment for acute lymphoblastic leukaemia, and most of it happens at home. By this stage the leukaemia is usually no longer visible on tests. Maintenance clears any cells still hiding, and giving it steadily for the full planned time is linked to fewer relapses. Your team will tell you the planned end date for your child's protocol.
Why the dose keeps changing
Children grow, catch colds and take other medicines, and each of these shifts the counts. A dose that suited your child in one season may be too much or too little a few months later. Regular changes mean the plan is working as designed. They are not a sign that something has gone wrong.
Too little can matter as much as too much. The goal is the most the marrow can safely take.The medicines
Which medicines make up a typical maintenance plan?
Protocols differ between hospitals and between risk groups. Most include some version of these four.
Mercaptopurine
A daily tablet, or a liquid where it is available, taken at home. This is the thiopurine whose dose depends on TPMT, NUDT15 and the blood counts.
At home
- Given at the same time each day
- Not crushed or split unless the team says so
- Handled with washed hands, stored away from children
Methotrexate by mouth
Taken once a week, on the same day each week. It is never meant to be daily. Mixing up the two schedules is one of the most dangerous medicine errors that can happen at home.
Mark the weekly day on a calendar the whole family can see.Steroid and vincristine pulses
Some protocols add short courses of steroid tablets and a vincristine injection at set intervals. Others have reduced or dropped them. Your child's plan will say which applies.
A preventive antibiotic
Many children take co-trimoxazole on set days to prevent one particular chest infection. It can lower counts a little too, which the team allows for when adjusting mercaptopurine.
Not sure whether this applies to you?
Ask an oncologistMonth by month
What does a month of maintenance look like at home?
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Tablets at home, every day
Give mercaptopurine at the time and in the way your team advised. Older advice to keep milk well away from the dose is applied less strictly in many protocols now, so follow your own team's instructions.
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A blood count at set intervals
Often every few weeks once your child is stable, and more often after a dose change or an infection. The test can usually be done at a laboratory near home and the report sent to the team.
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The team reads the counts and liver tests
They look at white cells, neutrophils, platelets and haemoglobin. They also check liver blood tests, because mercaptopurine can affect the liver.
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The dose goes up, down or pauses
If counts are higher than the target, the dose may rise. If they are too low, it is reduced or paused for a short while. Write down every change and the date it started.
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The cycle repeats until the planned end
Clinic visits in between cover growth, infections, pulses and school. Maintenance stops on the date set by the protocol, not when counts look good.
In the clinic
The words you will hear in maintenance clinic
- Maintenance
- The last and longest phase of leukaemia treatment, given mostly as tablets at home to stop the leukaemia returning.
- Neutrophils
- The white cells that fight bacterial infection. This is the count the team watches most closely when adjusting the dose.
- Target range
- The band the team wants the white cell count to sit in. Your child's protocol defines it.
- Dose adjustment
- Raising, lowering or briefly pausing mercaptopurine in response to blood counts, liver tests or illness.
- Adherence
- Taking every dose as planned. Studies have linked missed doses in maintenance with a higher chance of relapse.
- Relapse
- The leukaemia coming back after it had been cleared from tests.
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One thing that cannot wait
A fever during maintenance can be the first sign of a serious infection when white cells are low. If your child's temperature reaches thirty-eight degrees or more, or they are shivering, floppy or unusually drowsy, go to the nearest emergency department the same day and say they are on leukaemia treatment. Do not give paracetamol first and wait, because it hides the fever without treating the infection.
Being straight with you
What this page cannot tell you
It cannot tell you your child's dose or target range. Indian hospitals follow several different national and international protocols, and each sets its own numbers. Only your child's treating team knows which protocol and which risk group apply.
It cannot read the gene report
What your child's specific TPMT or NUDT15 variant means is a question for the oncologist or genetic counsellor who ordered the test. Rare variants may not be on every panel, and studies of NUDT15 in Indian children so far are small.
Who this does not apply to
Children with acute myeloid leukaemia, and most children with other cancers, are treated differently and usually have no mercaptopurine maintenance phase. Adults with acute lymphoblastic leukaemia take similar drugs, but their protocols and targets differ.
Where the evidence is mixed
Questions such as evening or morning dosing, and taking the tablet with food or milk, have been studied with mixed results. Trust your team's written instructions over advice from other parents or online groups.
Commonly believed
Four things parents believe about maintenance tablets
"Low counts mean the tablets are harming my child, so we should give less."
Some lowering of the white cell count is the intended target. It shows the drug is reaching the marrow. Only the team decides when counts are too low. Never change the dose on your own.
"If we miss a dose, we can double up tomorrow."
Do not double up unless the team tells you to. Missed doses do matter, but a double dose can push counts down too fast. Note the missed day and ask at the next contact.
"Maintenance is the easy part, so a few missed days make no difference."
It feels easier because your child is at home and looks well. Yet this is when steady daily dosing counts most. Studies have linked frequent missed doses with a higher chance of the leukaemia coming back.
"The gene test was normal, so the dose will never need changing."
The gene test sets the starting point. Growth, infections and other medicines all move the counts afterwards, so every child's dose changes during maintenance.
Questions we are asked
Common questions about maintenance dosing
How often will my child need blood tests?
It depends on the protocol and on how stable the counts are. A settled child is usually tested every few weeks. Expect more frequent tests after a dose change, an infection or a new medicine. Your team will give you a schedule and tell you where the test can be done.
Can mercaptopurine be given as a liquid?
A liquid form exists and makes small dose steps easier, but it is not stocked everywhere in India. If your child cannot swallow tablets, tell the team. Do not crush or split tablets without their advice, and wear gloves if you are told to handle them.
What if my child vomits soon after a dose?
Do not give another dose automatically. Note the time and tell the team at the next contact, or sooner if vomiting keeps happening. Repeated vomiting can mean an infection or another problem that needs checking, and it can also affect how much of the drug is absorbed.
Can my child go to school during maintenance?
Most children can, and many teams encourage it. Ask the school to tell you about chickenpox or measles in the class, and let the team know about any contact the same day. Good handwashing at home and school helps.
Can my child have vaccines during maintenance?
Live vaccines are usually avoided while the immune system is suppressed. Some other vaccines, such as the yearly flu vaccine, may be advised. Check with the team before any vaccination, including those offered in school or public health drives.
Why does the team keep checking liver tests?
Mercaptopurine can raise liver blood tests in some children. Mild rises are common and often settle with a dose change. Checking regularly lets the team adjust early, long before the liver is harmed.
Why was the dose cut when the gene test was normal?
A normal gene result removes one known reason for low counts, not every reason. Infections, other medicines such as co-trimoxazole, and the marrow's own recovery all affect counts. The team adjusts for whatever is happening now.
Does anyone else in the family need the gene test?
Not unless they are ever prescribed a thiopurine. The result carries no cancer risk for brothers or sisters. Keep a copy of your child's report, and mention it to any doctor who prescribes one of these drugs to a blood relative in future.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- National Cancer Institute — Childhood Acute Lymphoblastic Leukemia Treatment (PDQ) - Patient Version
- Clinical Pharmacogenetics Implementation Consortium (CPIC) — CPIC Guideline for Thiopurines and TPMT and NUDT15
- NCBI Medical Genetics Summaries — Mercaptopurine Therapy and TPMT and NUDT15 Genotype
- NHS — Acute lymphoblastic leukaemia: Treatment
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
TPMT and NUDT15 before thiopurinesWhat the two gene tests check before maintenance startsWhy NUDT15 matters especially in South AsiaWhy Indian children need NUDT15 tested, not just TPMTIntermediate metaboliser results and dose adjustmentIf the report shows one faulty copyCarrying your pharmacogenomic result for future careKeeping the result useful long after maintenance ends
Talk to us
Questions about your child's maintenance dose?
Bring the latest counts and the gene report, and a paediatric oncologist will talk you through how the dose is being managed. One helpline serves every CION centre.