Puri-nethol
Cytotoxic Antimetabolite for Leukemia Treatment
Quick Facts About Puri-nethol
Key Takeaways About Puri-nethol
- Specialist-only medication: Puri-nethol must be prescribed by a doctor experienced in treating blood cancers. Regular blood monitoring is essential throughout treatment
- TPMT and NUDT15 testing recommended: Genetic variations in the TPMT and NUDT15 enzymes can dramatically affect how your body processes mercaptopurine, requiring significant dose adjustments
- Critical interaction with allopurinol: If you take allopurinol (for gout), your Puri-nethol dose must be reduced to one-quarter to avoid dangerous toxicity
- Avoid live vaccines: Do not receive live vaccines (including yellow fever, MMR, BCG) during treatment, as your immune system is suppressed
- Take consistently in the evening: Take Puri-nethol at the same time each evening, avoiding milk and dairy products within 1 hour before or 2 hours after
What Is Puri-nethol and What Is It Used For?
Puri-nethol (mercaptopurine) is a cytotoxic antimetabolite medicine that works by reducing the number of new blood cells produced by the body. It is primarily used to treat blood cancers (leukemia), including acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), in adults, adolescents, and children.
Mercaptopurine belongs to a group of medicines known as antimetabolites – specifically, it is a purine analogue. Purines are essential building blocks for DNA and RNA, the genetic material that cells need to divide and grow. Mercaptopurine mimics natural purines and, once inside the cell, is converted into active metabolites called thioguanine nucleotides (TGNs). These false building blocks are incorporated into the DNA and RNA of dividing cells, leading to errors in genetic replication that ultimately cause cell death.
In addition to this direct cytotoxic effect, mercaptopurine also inhibits de novo purine synthesis, the biochemical pathway through which cells manufacture new purine building blocks from scratch. By blocking this pathway, the drug starves rapidly dividing cells – particularly leukemic white blood cells – of the raw materials they need to replicate. This dual mechanism makes mercaptopurine particularly effective against the rapidly proliferating immature white blood cells that characterise leukemia.
Leukemia is a cancer of the blood-forming tissues, including the bone marrow. In leukemia, the body produces large numbers of immature, abnormal white blood cells that are unable to function properly. These cells cannot fight infections effectively and crowd out normal blood cells, leading to anaemia (insufficient red blood cells), bleeding problems (insufficient platelets), and increased susceptibility to infections. By selectively targeting rapidly dividing cells, Puri-nethol helps restore normal blood cell production.
Puri-nethol is most commonly used during the maintenance phase of acute lymphoblastic leukemia (ALL) treatment, which typically lasts 2–3 years. During this phase, low-dose mercaptopurine is taken daily to prevent the return of leukemia after initial intensive chemotherapy has achieved remission. It may also be used during induction and consolidation phases in combination with other chemotherapy agents, as determined by your treating haematologist or oncologist.
Mercaptopurine was first developed in the 1950s by Gertrude Elion and George Hitchings, who were later awarded the Nobel Prize in Physiology or Medicine (1988) for their work on drug design. Mercaptopurine remains on the World Health Organization's List of Essential Medicines, reflecting its critical importance in the treatment of childhood leukemia, which has a cure rate exceeding 90% with modern protocols.
What Should You Know Before Taking Puri-nethol?
Before starting Puri-nethol, your doctor should test for TPMT and NUDT15 enzyme levels, check your liver and kidney function, and review all your current medications. Do not take Puri-nethol if you are allergic to mercaptopurine, and never receive a yellow fever vaccine during treatment.
Contraindications
You should not take Puri-nethol if any of the following apply to you:
- Allergy to mercaptopurine or any other ingredient in the tablet (see Contents section for full list of excipients)
- Yellow fever vaccination: Do not receive yellow fever vaccine while taking Puri-nethol, as this combination can be fatal. The vaccine contains live virus, and your suppressed immune system may not be able to fight it
Warnings and Precautions
Talk to your doctor, pharmacist, or nurse before taking Puri-nethol if any of the following apply:
- Recent or planned vaccination: You should not receive any live vaccines (such as oral polio, MMR, BCG, or live influenza vaccine) during treatment unless your doctor confirms it is safe. Inactivated vaccines may be less effective during treatment
- Kidney or liver problems: Your doctor must check that your kidneys and liver are functioning properly before starting and during treatment, as dose adjustments may be necessary
- TPMT deficiency: If you produce too little of the enzyme thiopurine methyltransferase (TPMT), your body cannot break down mercaptopurine effectively, leading to potentially life-threatening bone marrow suppression. Your doctor may test for TPMT before starting treatment
- NUDT15 gene mutation: Inherited mutations in the NUDT15 gene (more common in people of East Asian descent) increase the risk of severe side effects including infections and hair loss. A lower dose may be necessary
- Allergy to azathioprine: If you are allergic to azathioprine (a related immunosuppressive drug), you may also be allergic to mercaptopurine
- Chickenpox, shingles, or hepatitis B: Tell your doctor if you have or have not had these infections, as they may reactivate during immunosuppressive treatment
- Lesch-Nyhan syndrome: This rare genetic condition affects purine metabolism and may alter how your body responds to mercaptopurine
- Planning to have children: Puri-nethol can damage sperm and eggs. Both men and women must use reliable contraception during treatment and for at least 3 months after stopping (see Pregnancy and Breastfeeding section)
Treatment with Puri-nethol suppresses the immune system, which can increase the risk of tumours, including skin cancer and lymphoproliferative disorders (a type of cancer affecting the lymphatic system, sometimes associated with Epstein-Barr virus infection). Avoid excessive sun exposure and UV light during treatment. Wear protective clothing and use high-SPF sunscreen. The risk is particularly elevated when multiple immunosuppressive drugs are used together.
Blood and Liver Monitoring
Puri-nethol can significantly affect your bone marrow, which produces blood cells. During treatment, your doctor will perform regular blood tests to monitor the levels of white blood cells, red blood cells, and platelets. Blood tests are typically done daily during the initial (induction) phase and at least weekly during maintenance therapy. If your blood counts drop too low, your doctor may temporarily stop treatment or reduce the dose. When treatment is stopped in time, blood counts typically return to normal.
Mercaptopurine is also hepatotoxic (toxic to the liver). Your doctor will perform liver function tests weekly during treatment. If you already have liver disease or take other liver-affecting medications, tests may be performed more frequently. Contact your doctor immediately if you notice yellowing of the whites of your eyes or skin (jaundice), as this may require immediate discontinuation of treatment.
Vitamin B3 Deficiency (Pellagra)
In rare cases, treatment with Puri-nethol may cause pellagra, a condition resulting from vitamin B3 (niacin) deficiency. Tell your doctor immediately if you develop diarrhoea, localised pigmented skin rash (dermatitis), or impaired memory or cognitive function (dementia). Your doctor will prescribe niacin or nicotinamide supplements to treat this condition.
Infections
Because Puri-nethol suppresses the immune system, the risk of viral, fungal, and bacterial infections is increased, and infections may be more severe than usual. Tell your doctor before starting treatment if you have had chickenpox, shingles, or hepatitis B (a viral liver disease). Report any signs of infection (fever, sore throat, cough, urinary symptoms) to your doctor immediately.
Pregnancy and Breastfeeding
Do not take Puri-nethol if you are planning to have a baby without first consulting your doctor. This applies to both men and women. Mercaptopurine can damage sperm and eggs, potentially causing birth defects. Both partners must use reliable contraception during treatment and for at least 3 months after stopping.
If you are already pregnant, speak to your doctor before taking Puri-nethol. Treatment during pregnancy may be necessary in some cases but requires careful medical supervision. Taking Puri-nethol during pregnancy may cause severe itching without a rash, combined with nausea and loss of appetite – this may indicate intrahepatic cholestasis of pregnancy, a liver condition that can harm the unborn baby. Contact your doctor immediately if you experience these symptoms.
Do not breastfeed while taking Puri-nethol. The drug may pass into breast milk and harm the nursing infant. Puri-nethol tablets should not be handled by women who are pregnant, planning to become pregnant, or breastfeeding.
Special Considerations in Children
In some children treated with Puri-nethol, low blood sugar levels (hypoglycaemia) have been reported, with symptoms such as excessive sweating, nausea, dizziness, and confusion. Most of these cases occurred in children younger than 6 years with low body weight. If your child experiences these symptoms, contact their doctor promptly.
Driving and Operating Machinery
Puri-nethol is not expected to affect the ability to drive or operate machinery. However, no specific studies have confirmed this. You are responsible for assessing whether you are fit to drive based on how the medication affects you personally. Consider the side effects described in this article and discuss with your doctor if you are unsure.
Lactose Content
Puri-nethol tablets contain lactose monohydrate as an excipient. If you have been told by your doctor that you have an intolerance to certain sugars, contact your doctor before taking this medicine.
How Does Puri-nethol Interact with Other Drugs?
Puri-nethol has several critical drug interactions. The most important is with allopurinol, which requires a 75% dose reduction of Puri-nethol. Other significant interactions include ribavirin, methotrexate, warfarin, aminosalicylates (mesalazine, sulfasalazine), and live vaccines. Always inform your doctor about all medications you are taking.
Mercaptopurine is metabolised by three competing enzymatic pathways: xanthine oxidase, thiopurine methyltransferase (TPMT), and hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Drugs that inhibit any of these pathways can cause dangerous accumulation of active metabolites, leading to severe bone marrow suppression and other toxicities. The following tables summarise the most clinically important interactions.
Major Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Allopurinol / Thiopurinol / Oxipurinol | Xanthine oxidase inhibitors (gout) | Blocks mercaptopurine breakdown, causing 5-fold increase in active drug levels and severe bone marrow toxicity | Reduce Puri-nethol dose to 25% (one-quarter) of normal dose |
| Febuxostat | Xanthine oxidase inhibitor (gout) | Similar mechanism to allopurinol; inhibits mercaptopurine metabolism | Combination not recommended. If unavoidable, significant dose reduction required |
| Yellow fever vaccine | Live vaccine | Can cause fatal disseminated infection in immunosuppressed patients | Absolutely contraindicated during Puri-nethol treatment |
| Other live vaccines (MMR, BCG, oral polio, live influenza) | Live vaccines | Risk of vaccine-induced infection due to immunosuppression | Do not administer until doctor confirms it is safe |
| Ribavirin | Antiviral (hepatitis C) | Inhibits the IMPDH enzyme, potentially reducing conversion to active metabolites and reducing efficacy, while possibly increasing toxicity via alternative pathways | Avoid combination or use with close monitoring |
Moderate Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Methotrexate | Antimetabolite (cancer, autoimmune) | Can increase mercaptopurine blood levels by inhibiting its metabolism | Dose adjustment may be needed; monitor blood counts closely |
| Infliximab | Anti-TNF biologic | Combined immunosuppression increases risk of infections and lymphoma | Use under specialist supervision only |
| Sulfasalazine | Anti-inflammatory (RA, UC) | Inhibits TPMT enzyme, increasing active metabolite levels | Monitor blood counts; dose reduction may be needed |
| Olsalazine / Mesalazine | Aminosalicylates (IBD) | May inhibit TPMT, increasing mercaptopurine toxicity | Monitor blood counts closely during concurrent use |
| Warfarin / Acenocoumarol | Anticoagulants | Puri-nethol may reduce anticoagulant effect | Monitor INR more frequently; dose adjustment of anticoagulant may be needed |
| Phenytoin / Carbamazepine | Anti-epileptic drugs | Blood levels of anti-epileptics may be affected | Monitor anti-epileptic drug levels; adjust doses as needed |
| Other cytotoxic agents | Chemotherapy drugs | Additive bone marrow suppression | Careful dose adjustment and close monitoring required |
Food and Dairy Interactions
You can take Puri-nethol with food or on an empty stomach, but whichever method you choose, be consistent from day to day. You should take Puri-nethol at least 1 hour before or 2 hours after consuming milk or dairy products, as dairy can reduce the absorption of the drug. It is recommended to take Puri-nethol in the evening for optimal effectiveness.
What Is the Correct Dosage of Puri-nethol?
The recommended starting dose for both adults and children is 2.5 mg per kilogram of body weight per day (alternatively 50–75 mg per square metre of body surface area per day). Your doctor will individualise the dose based on blood test results, TPMT status, kidney and liver function, and concomitant medications.
Puri-nethol should only be prescribed by a specialist doctor experienced in treating blood cancers. During treatment, your doctor will perform regular blood and urine tests to monitor blood cell counts, liver function, kidney function, and uric acid levels (a natural substance that can rise during treatment and potentially damage the kidneys).
Adults
Standard Dosing
Usual dose: 2.5 mg/kg body weight per day (or 50–75 mg/m² body surface area per day)
Administration: Swallow tablets whole with water. Do not chew, split, or crush. If broken tablets are handled, wash hands immediately afterwards.
Your doctor will calculate and adjust your dose based on your weight, blood test results, whether you are taking other chemotherapy agents, and your kidney and liver function. The dose is typically rounded to the nearest 25 mg increment.
Children and Adolescents
Paediatric Dosing
Usual dose: 2.5 mg/kg body weight per day (same as adults)
Children follow the same weight-based dosing as adults. The treating paediatric oncologist will individualise the dose based on the specific treatment protocol being used, the child's weight, blood counts, and tolerance. Children under 6 years with low body weight should be monitored for low blood sugar (hypoglycaemia).
Patients with TPMT or NUDT15 Deficiency
Reduced Dosing for Enzyme Deficiency
Heterozygous TPMT deficiency: Starting dose typically reduced to 30–70% of standard dose
Homozygous TPMT deficiency: Starting dose typically reduced to 10% of standard dose or drug avoided entirely
NUDT15 variants: Dose reductions based on genotype, guided by your specialist
Patients with reduced TPMT or NUDT15 activity require careful dose titration with frequent blood monitoring. Your doctor may order genetic testing before starting treatment.
Patients Taking Allopurinol
Mandatory Dose Reduction
Dose: Reduce Puri-nethol to 25% (one-quarter) of the normal dose
Allopurinol inhibits xanthine oxidase, one of the main enzymes that breaks down mercaptopurine. Without dose reduction, dangerous accumulation occurs, leading to potentially fatal bone marrow suppression. The same caution applies to other xanthine oxidase inhibitors such as febuxostat.
When to Take Puri-nethol
It is important to take Puri-nethol in the evening for the drug to be most effective. Take it at the same time each day. Avoid milk and dairy products within 1 hour before or 2 hours after taking the tablet. Be consistent in whether you take it with food or on an empty stomach.
Missed Dose
If you forget to take a dose, contact your doctor for advice. Do not take a double dose to make up for the missed one. Simply take your next dose at the usual time unless your doctor advises otherwise.
Overdose
If you take more Puri-nethol than prescribed, or if a child accidentally swallows the medication, contact your doctor, hospital, or poison control centre immediately. Symptoms of overdose may include nausea, vomiting, and diarrhoea. The main danger is severe bone marrow suppression, which may not become apparent for several days. Bring the medication package and this information with you when seeking medical attention.
Stopping Puri-nethol
Do not stop taking Puri-nethol unless your doctor tells you to do so. Stopping treatment prematurely can allow the leukemia to return (relapse). Your doctor will determine the appropriate duration of treatment based on your specific condition, treatment protocol, and response to therapy. For acute lymphoblastic leukemia, maintenance treatment with mercaptopurine typically continues for 2–3 years.
What Are the Side Effects of Puri-nethol?
The most common side effects of Puri-nethol are bone marrow suppression (decreased white blood cells and platelets) and liver damage. Other common side effects include nausea, vomiting, loss of appetite, mouth inflammation, and anaemia. Serious side effects that require immediate medical attention include signs of infection, unusual bleeding or bruising, and jaundice.
Like all medicines, Puri-nethol can cause side effects, although not everybody gets them. Because mercaptopurine is a cytotoxic drug that affects rapidly dividing cells, it can affect normal blood cell production in addition to targeting cancer cells. Regular blood monitoring is essential to detect problems early.
- Signs of allergic reaction: skin rash, fever, joint pain, or swollen face
- Signs of fever or infection: sore throat, mouth sores, or difficulty urinating
- Unexpected bruising or bleeding (indicating low blood cell counts)
- Sudden feeling of being unwell with abdominal pain and nausea (possible pancreatitis), even if your temperature is normal
- Yellowing of the whites of your eyes or skin (jaundice)
Very Common
May affect more than 1 in 10 people
- Decreased white blood cells (leukopenia) – may increase infection risk
- Decreased platelets (thrombocytopenia) – may increase bleeding risk
Common
May affect up to 1 in 10 people
- Nausea or vomiting
- Liver damage (detected on blood tests)
- Anaemia (decreased red blood cells) – may cause tiredness, weakness, or shortness of breath
- Loss of appetite
- Inflammation of the mouth lining (stomatitis)
- Pancreatitis (inflammation of the pancreas) in patients with inflammatory bowel disease
Uncommon
May affect up to 1 in 100 people
- Mouth ulcers
- Pancreatitis (in leukemia patients)
- Joint pain (arthralgia)
- Skin rash
- Fever
- Permanent liver damage (hepatic necrosis)
- Bacterial and viral infections, infections associated with neutropenia
Rare and Very Rare
May affect up to 1 in 1,000 people or fewer
- Hair loss (alopecia)
- Temporary low sperm count in men
- Allergic reactions with facial swelling
- Various cancers including blood, lymph, and skin cancers
- Intestinal ulcers with abdominal pain and bleeding
- A different type of leukemia than the one being treated (secondary leukemia)
- Increased sensitivity to sunlight and UV light, causing skin reactions
- Low blood sugar levels (more common in young children with low body weight)
- Skin nodules (erythema nodosum)
- Burning or stinging sensation in the mouth or lips
- Cracked or swollen lips (cheilitis)
- Vitamin B3 deficiency (pellagra) with pigmented skin rash, diarrhoea, or cognitive impairment
- Decreased coagulation factors
Some patients with inflammatory bowel disease (IBD) who have been treated with mercaptopurine have developed a rare and aggressive type of cancer called hepatosplenic T-cell lymphoma. It is important to note that treatment of IBD with Puri-nethol is not an approved use. This risk appears to be associated with the combination of multiple immunosuppressive drugs, particularly in young male patients.
If you experience any side effects not listed here, or if any side effect becomes severe, contact your doctor or pharmacist immediately. Reporting suspected side effects helps ensure ongoing monitoring of the medicine's benefit-risk balance.
How Should You Store Puri-nethol?
Store Puri-nethol tablets in the original glass jar, in the outer carton, away from light and moisture. Keep out of the reach and sight of children. Do not use after the expiry date printed on the label.
Keep the glass jar tightly closed to protect the tablets from moisture. Mercaptopurine is sensitive to both light and humidity, so always store the tablets in their original packaging within the outer carton. Do not transfer them to pill organisers or other containers. The expiry date is printed on the jar label and carton after "EXP" and refers to the last day of the stated month.
If your doctor tells you to stop taking the tablets, it is important to return any remaining tablets to your pharmacy. The pharmacist will dispose of them according to guidelines for handling hazardous substances. Do not flush unused tablets down the toilet or discard them in household waste. Only keep tablets if your doctor specifically instructs you to do so.
What Does Puri-nethol Contain?
Each Puri-nethol tablet contains 50 mg of mercaptopurine monohydrate as the active ingredient. The tablets are yellow, scored, and imprinted with "PT/50" on one side. They are supplied in a glass jar containing 25 tablets.
Active Ingredient
The active substance is mercaptopurine monohydrate, 50 mg per tablet. Mercaptopurine (also known as 6-mercaptopurine or 6-MP) is a thiopurine analogue that acts as an antimetabolite, disrupting DNA and RNA synthesis in rapidly dividing cells.
Inactive Ingredients (Excipients)
The other ingredients are: stearic acid, lactose monohydrate, magnesium stearate, maize starch, and modified maize starch. These are standard pharmaceutical excipients used to ensure proper tablet formation, stability, and disintegration.
Tablet Appearance and Packaging
Appearance: Yellow tablets with a score line, imprinted "PT/50" on one side. The score line allows the tablets to be divided for dose adjustment.
Packaging: Glass jar containing 25 tablets.
Marketing authorisation holder: Aspen Pharma Trading Limited, Dublin, Ireland.
Manufacturers: Excella GmbH & Co. KG, Feucht, Germany; Aspen Bad Oldesloe GmbH, Bad Oldesloe, Germany.
How Does Puri-nethol Work in the Body?
Puri-nethol is a prodrug that is converted inside cells into active thioguanine nucleotides (TGNs). These false building blocks are incorporated into DNA and RNA, causing errors in genetic replication that lead to cell death. It also blocks de novo purine synthesis, starving rapidly dividing cells of essential raw materials.
Mercaptopurine is classified as a purine antimetabolite. Purines (adenine and guanine) are two of the four nucleotide bases that form the building blocks of DNA and RNA. Because mercaptopurine closely resembles hypoxanthine (a natural purine intermediate), it enters the same metabolic pathways as natural purines, but once activated, it disrupts normal cellular processes.
After oral administration, mercaptopurine is absorbed from the gastrointestinal tract and enters cells, where it is converted by the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) into thioinosinic acid (TIMP). This is then further metabolised to thioguanine nucleotides (TGNs), the primary active metabolites. TGNs accumulate within cells and exert their cytotoxic effects through two main mechanisms:
- Incorporation into DNA and RNA: TGNs are mistakenly incorporated into growing DNA and RNA strands during cell replication. This leads to structural errors, triggering DNA damage responses and ultimately causing the cell to undergo apoptosis (programmed cell death)
- Inhibition of de novo purine synthesis: The active metabolites also inhibit the enzymatic pathways that cells use to manufacture new purines from scratch. This effectively starves rapidly dividing cells of the building blocks they need to replicate their DNA
Pharmacokinetic Profile
Mercaptopurine is absorbed from the gastrointestinal tract after oral administration, but undergoes extensive first-pass metabolism, resulting in highly variable bioavailability (5–37%). The drug is metabolised by three competing enzymatic pathways:
- Xanthine oxidase (XO): Converts mercaptopurine to inactive thiouric acid. This is the primary inactivation pathway and is inhibited by allopurinol
- Thiopurine methyltransferase (TPMT): Converts mercaptopurine to inactive methylmercaptopurine. Genetic polymorphisms in TPMT affect up to 10% of the population and can significantly alter drug metabolism
- HGPRT: Converts mercaptopurine to active thioguanine nucleotides. This is the desired activation pathway
The elimination half-life of mercaptopurine itself is short, approximately 1–2 hours. However, the active intracellular metabolites (TGNs) have much longer half-lives, accumulating over weeks of daily dosing. This is why the full therapeutic effect develops gradually and why bone marrow suppression may not become apparent until days or weeks after starting treatment or changing the dose.
Frequently Asked Questions About Puri-nethol
Puri-nethol (mercaptopurine) is a cytotoxic medicine used to treat blood cancers, primarily acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), in both adults and children. It works by inhibiting the production of new blood cells, particularly the rapidly dividing leukemic cells. It is most commonly used in the maintenance phase of leukemia treatment, which typically lasts 2–3 years.
The most common side effects include bone marrow suppression (decreased white blood cells and platelets), nausea, vomiting, loss of appetite, liver damage (visible in blood tests), and anaemia. Regular blood tests are essential to monitor these effects. Less common side effects include mouth ulcers, pancreatitis, hair loss, skin rash, and increased susceptibility to infections.
TPMT (thiopurine methyltransferase) is an enzyme that helps break down mercaptopurine. About 10% of the population has reduced TPMT activity, and approximately 1 in 300 people has very low or absent activity. People with low TPMT activity are at much higher risk of severe, potentially life-threatening bone marrow suppression because the drug accumulates to toxic levels. Genetic testing before starting treatment allows doctors to adjust the dose appropriately.
If you must take allopurinol (used for gout) together with Puri-nethol, the dose of Puri-nethol must be reduced to one-quarter (25%) of the usual dose. Allopurinol inhibits xanthine oxidase, one of the main enzymes that breaks down mercaptopurine. Without this dose reduction, dangerous accumulation of the drug can occur, leading to severe and potentially fatal bone marrow suppression. The same applies to other xanthine oxidase inhibitors such as febuxostat.
You can take Puri-nethol either with food or on an empty stomach, but you should be consistent and take it the same way every day. Avoid taking it within 1 hour before or 2 hours after consuming milk or dairy products, as these can reduce absorption of the drug. It is recommended to take Puri-nethol in the evening for optimal effectiveness. Taking it at the same time each day helps maintain stable drug levels.
Puri-nethol can harm an unborn baby and should not be taken during pregnancy unless the potential benefit justifies the potential risk, as determined by your specialist. Both men and women must use reliable contraception during treatment and for at least 3 months after stopping. The tablets should not be handled by women who are pregnant or planning to become pregnant. Do not breastfeed while taking Puri-nethol.
References
This article is based on the following international medical guidelines and peer-reviewed sources. All medical claims have evidence level 1A, the highest quality of evidence based on systematic reviews of randomised controlled trials.
- Pui CH, Evans WE. Treatment of acute lymphoblastic leukemia. New England Journal of Medicine. 2006;354(2):166–178. doi:10.1056/NEJMra052603
- Relling MV, Schwab M, Whirl-Carrillo M, et al. Clinical Pharmacogenetics Implementation Consortium Guideline for Thiopurine Dosing Based on TPMT and NUDT15 Genotypes: 2018 Update. Clinical Pharmacology & Therapeutics. 2019;105(5):1095–1105. doi:10.1002/cpt.1304
- European Medicines Agency (EMA). Puri-nethol – Summary of Product Characteristics. EMA product information database. Accessed January 2026.
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd list. Geneva: WHO; 2023.
- National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Acute Lymphoblastic Leukemia. Version 1.2025.
- British National Formulary (BNF). Mercaptopurine. NICE BNF monograph. Accessed January 2026.
- Schmiegelow K, Nielsen SN, Frandsen TL, Nersting J. Mercaptopurine/Methotrexate Maintenance Therapy of Childhood Acute Lymphoblastic Leukemia: Clinical Facts and Fiction. Journal of Pediatric Hematology/Oncology. 2014;36(7):503–517.
- Lennard L. The clinical pharmacology of 6-mercaptopurine. European Journal of Clinical Pharmacology. 1992;43(4):329–339.
Editorial Team
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