Thioguanine
Thioguanine is an oral chemotherapy medicine used to treat certain acute leukemias, specifically acute nonlymphocytic leukemias, usually alongside other cancer drugs.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 1 clinical label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
Thioguanine (Tabloid) is an older oral chemotherapy, on the U.S. market since about 1966, used with other cancer drugs to get acute nonlymphocytic leukemias (also called acute myeloid leukemia) into remission and keep them there. It poses as a DNA and RNA building block, blocking cancer cells from making the real ones and getting built into their genetic material. Nausea, vomiting, poor appetite and mouth sores are what most people notice. The two things to watch are falling blood counts (call your oncology team right away for fever or unusual bleeding) and liver damage, which is why it comes with frequent blood tests and is kept to short courses.
Clinical pearls
- Ask whether TPMT and NUDT15 were tested, since inherited low levels of these enzymes can call for a much lower dose.
- Make sure anyone prescribing mesalamine, sulfasalazine or olsalazine knows you take it, because these bowel medicines can deepen the drop in blood counts.
- Unlike with mercaptopurine or azathioprine, allopurinol for high uric acid does not require a thioguanine dose change.
- It may harm an unborn baby, so women who could become pregnant should avoid pregnancy while taking it.
Patient information guide A plain-language walkthrough of Thioguanine, written from its FDA label.
What Thioguanine is used for
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Thioguanine is used in leukemia treatment, as follows:
- Tabloid brand thioguanine is used by mouth for remission induction and remission consolidation in acute nonlymphocytic leukemias.
- It is usually combined with other chemotherapy, since combinations work better than thioguanine alone for starting remission.
- It is not recommended for maintenance or long-term continuous therapy.
- It is not effective for chronic lymphocytic leukemia, Hodgkin’s lymphoma, multiple myeloma, or solid tumors.
- For chronic myelogenous leukemia, busulfan is usually the preferred drug.
How Thioguanine works
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Cells convert thioguanine into an active form that interferes with making purines, which are building blocks of DNA and RNA. It is also built into DNA and RNA itself. This disrupts cancer cell growth.
Its effects are complex, and no single site of action has been identified.
Thioguanine dosage
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Tabloid brand thioguanine is taken by mouth. The total daily dose may be given at one time. Your dose depends on the stage and type of leukemia and on other medicines in your treatment plan.
- People with TPMT or NUDT15 deficiency may need a much lower starting dose.
- Your doctor may adjust the dose based on blood counts and side effects.
- Follow your prescriber’s instructions and the label exactly.
Dosing details from the FDA-approved label
From the Thioguanine prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.
- Single-agent chemotherapy with thioguanine (pediatric patients and adults)
- Usual initial dosage approximately 2 mg/kg of body weight per day
- If, after 4 weeks on this dosage, there is no clinical improvement and no leukocyte or platelet depression, the dosage may be cautiously increased to 3 mg/kg/day
- The total daily dose may be given at one time
- Dosage does not depend on whether the patient is receiving ZYLOPRIM (allopurinol)
- Patients with homozygous TPMT or NUDT15 deficiency
- Typically require 10% or less of the standard thioguanine dosage
- Reduce initial dosage
- Known homozygous TPMT or NUDT15 deficiency
- Patients with heterozygous TPMT or NUDT15 deficiency
- Most tolerate recommended thioguanine doses, but some require dose reduction based on toxicities
- Reduce the dosage based on tolerability
- Patients heterozygous for both TPMT and NUDT15 may require more substantial dosage reduction
- Pediatric acute nonlymphocytic leukemia (multiple-drug protocol)
- Multiple-drug protocol including thioguanine, prednisone, cytarabine, cyclophosphamide, and vincristine
- Remission maintained with daily thioguanine, 4-day pulses of cytarabine and cyclophosphamide, and a single dose of vincristine every 28 days
- Adult acute nonlymphocytic leukemias (combination therapy)
- Combination of thioguanine and cytarabine according to a protocol developed at The Memorial Sloan-Kettering Cancer Center, followed by a multiple-drug maintenance regimen which included thioguanine
Read the label’s full dosing text
DOSAGE AND ADMINISTRATION TABLOID brand Thioguanine is administered orally. The dosage which will be tolerated and effective varies according to the stage and type of neoplastic process being treated. Because the usual therapies for adult and pediatric acute nonlymphocytic leukemias involve the use of thioguanine with other agents in combination, physicians responsible for administering these therapies should be experienced in the use of cancer chemotherapy and in the chosen protocol. Patients with homozygous deficiency of either TPMT or NUDT15 enzyme typically require 10% or less of the standard thioguanine dosage. Reduce initial dosage in patients who are known to have homozygous TPMT or NUDT15 deficiency. Most of the patients with heterozygous TPMT or NUDT15 deficiency tolerate recommended thioguanine doses, but some require dose reduction based on toxicities. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dosage reduction. Reduce the dosage based on tolerability. Ninety-six (59%) of 163 pediatric patients with previously untreated acute nonlymphocytic leukemia obtained complete remission with a multiple-drug protocol including thioguanine, prednisone, cytarabine, cyclophosphamide, and vincristine. Remission was maintained with daily thioguanine, 4-day pulses of cytarabine and cyclophosphamide, and a single dose of vincristine every 28 days. The median duration of remission was 11.5 months. Fifty-three percent of previously untreated adults with acute nonlymphocytic leukemias attained remission following use of the combination of thioguanine and cytarabine according to a protocol developed at The Memorial Sloan-Kettering Cancer Center. A median duration of remission of 8.8 months was achieved with the multiple-drug maintenance regimen which included thioguanine. On those occasions when single-agent chemotherapy with thioguanine may be appropriate, the usual initial dosage for pediatric patients and adults is approximately 2 mg/kg of body weight per day. If, after 4 weeks on this dosage, there is no clinical improvement and no leukocyte or platelet depression, the dosage may be cautiously increased to 3 mg/kg/day. The total daily dose may be given at one time.
Excerpted — the section continues on the label. Read the full Dosage and Administration section on DailyMed →
Thioguanine side effects
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The most common effect is lowered blood counts. Others include:
Common side effects
- Low blood counts (bone marrow suppression)
- High uric acid levels
- Nausea
- Vomiting
- Loss of appetite
- Mouth sores (stomatitis)
When to get medical help
- Call your doctor right away for signs of infection or unusual bleeding, which can result from low blood counts.
- Get help for yellowing of the skin or eyes, a tender belly, swelling or fluid buildup, or sudden weight gain. These can be signs of liver toxicity.
- Tell your doctor about severe belly pain, since intestinal damage has been reported with combination chemotherapy that included thioguanine.
- Report symptoms of overdose, such as nausea, vomiting, feeling unwell, low blood pressure, or heavy sweating.
Thioguanine warnings and precautions
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- Bone marrow suppression is the biggest dose-related risk. It can lead to serious infections and bleeding. Frequent blood counts are needed.
- Liver toxicity is a high risk with long-term continuous use, especially in males. It often reverses after stopping.
- Inherited TPMT deficiency raises the risk of severe bone marrow suppression. Testing may not catch everyone at risk, so monitoring still matters.
- It may cause fetal harm.
Thioguanine interactions
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A few drug combinations need care:
- Olsalazine, mesalazine, sulphasalazine: may inhibit TPMT and worsen bone marrow suppression.
- Other drugs that suppress bone marrow: the thioguanine dose may need to be lowered.
- Allopurinol: no thioguanine dose reduction is needed, unlike with mercaptopurine or azathioprine.
Interactions listed in the FDA-approved label
From the Thioguanine prescribing information (“Drug Interactions”): what the manufacturer studied or reported to the FDA.
- PURINETHOL (mercaptopurine): There is usually complete cross-resistance between mercaptopurine and TABLOID brand Thioguanine.
- Aminosalicylate derivatives (e.g., olsalazine, mesalazine, or sulphasalazine): There is in vitro evidence that they inhibit the TPMT enzyme. Administer with caution to patients receiving concurrent thioguanine therapy (see WARNINGS).
Read the label’s full interactions text
Drug Interactions There is usually complete cross-resistance between PURINETHOL (mercaptopurine) and TABLOID brand Thioguanine. As there is in vitro evidence that aminosalicylate derivatives (e.g., olsalazine, mesalazine, or sulphasalazine) inhibit the TPMT enzyme, they should be administered with caution to patients receiving concurrent thioguanine therapy (see WARNINGS).
Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.
Before taking Thioguanine
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- Do not use it if your disease has shown resistance to thioguanine.
- Tell your doctor if you have TPMT or NUDT15 deficiency.
- Avoid pregnancy while taking it. Discuss risks with your doctor.
- Males may have higher liver toxicity risk.
- Share all your medicines, including aminosalicylates.
Thioguanine overdose
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Overdose can cause nausea, vomiting, feeling unwell, low blood pressure, and sweating right away. Low blood counts and kidney-related lab changes can appear later. There is no known antidote, so the drug is stopped and treatment is supportive, such as transfusions or antibiotics.
What Thioguanine does in the body
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Thioguanine is built into the DNA and RNA of bone marrow cells. With repeated daily doses, much more is incorporated than after a single dose. Its active forms last much longer in cells than the drug does in blood.
How your body processes Thioguanine
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Absorption by mouth is incomplete and variable, averaging about 30% of a dose. The body quickly converts it to other substances, and very little unchanged drug appears in urine. Active forms in cells last longer than the drug in plasma, so blood levels are of questionable value for monitoring. It is not expected to reach useful levels in spinal fluid.
How to store Thioguanine
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Store at 15° to 25°C (59° to 77°F) in a dry place.
Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
Supplements & herbs that interact with Thioguanine
17 supplements and herbal products have documented interactions with Thioguanine in the licensed clinical database we use. Most are manageable — but your pharmacist should know about everything you take, including vitamins and herbals.
- Major · 1
- Moderate · 7
- Minor · 9
Educational information from a licensed clinical database (Natural Medicines) — see our data sources & update cadence. Not medical advice: an interaction being documented does not mean it will happen to you; do not start or stop medications or supplements without professional guidance.
Thioguanine: pharmacist answers to common questions
Quick, plain-English answers to the questions patients ask most about Thioguanine — the kind of thing our pharmacy team would talk through with you at the counter.
What is thioguanine for?
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How do I take it?
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What side effects should I expect?
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When should I call my doctor?
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Do other medicines matter?
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Is it safe in pregnancy?
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Is Thioguanine available over the counter?
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When was Thioguanine first available?
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Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
More about Thioguanine on HelloPharmacist
Thioguanine forms and strengths (how it comes)
Thioguanine is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Need a version that does not list lactose, a gluten source, a dye or gelatin? Inactive ingredients differ by manufacturer: see Thioguanine inactive ingredients by manufacturer.
Tablet
How this form is used
- Tabloid is used for remission induction and consolidation in acute nonlymphocytic leukemias.
- Tabloid is not recommended for maintenance or other long-term continuous therapy.
- Tabloid is taken by mouth.
- Tabloid’s total daily dose may be given at one time.
- Tabloid dosing depends on disease type and stage, and is set by your doctor.
Thioguanine on the U.S. market: products, makers and brands
How Thioguanine appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
1 company lists 1 Thioguanine product record with the FDA, mostly as tablet; the earliest marketing or approval year on record is 1966. Brand names on the directory include Tabloid; the rest are generics.
Also listed with the FDA, not a patient dose form: Powder (1) — bulk drug substance sold to compounders/manufacturers and multi-item kits. These aren’t counted in the dose-form total above.
Compare Thioguanine products
A representative set of FDA-listed product records for Thioguanine — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Tablet | ||||
| 40 mg | Oral | Waylis Therapeutics LLC | NDA | View NDC → |
Showing 1 of 1 products — FDA National Drug Code Directory. See every product, package size and price: browse all 1 Thioguanine NDCs →
Thioguanine side effects reported to the FDA (FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Thioguanine — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Thioguanine in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
Thioguanine FDA approval history
How Thioguanine went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
Thioguanine recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
The FDA’s enforcement reports list no Thioguanine recalls since July 2021.
✅No Thioguanine recalls on record since July 2021Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Sep 24, 2026.
RxNorm Concept Web — From Ingredient to Every Form and Strength
This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.
RxCUI 10485 1 dose form · 1 strength
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Dose form (SCDF) Oral Tablet RxCUI 374104In current FDA listingsClinical drug / strength (SCD) 40 MGRxCUI 198269
Look up RxCUI 10485 in the RxCUI Atlas →
RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.
Thioguanine supply and shortage status
Whether Thioguanine is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
Thioguanine brand names
Thioguanine is sold under one brand name in the FDA directory — Tabloid. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.
Who makes Thioguanine: manufacturers and labelers
One company lists Thioguanine products with the FDA. By number of product records, the largest are Waylis Therapeutics LLC. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.
Thioguanine drug class (RxNorm)
Thioguanine belongs to the Antimetabolite class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
Sources for this Thioguanine page
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How this page is built
HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. Waylis Therapeutics LLC is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →