Tioguanine
Antimetabolites
AntimetabolitesHigh alert
An error with this medicine can cause serious harm: double checks and protocols are used.
Oral thiopurine for acute myeloid leukaemia. Like mercaptopurine it forms thioguanine nucleotides; inherited enzyme deficiencies and liver damage are the risks.
Also called: thioguanine, 6-thioguanine, 6-TG
Quick facts
- Group
- Antimetabolites
- Target
- DNA/RNA and purine synthesis, through thioguanine nucleotides
- Used for
- Acute myeloid leukaemia
- Key effects
- Nausea · Mouth and throat sores · Myelosuppression
- Monitor
- Complete blood count regularly
- ATC
- L01BB03
No doses: the clinician sets them by the current guideline.
Mechanism of action
Tioguanine is a sulfur analogue of guanine. The salvage enzyme HGPRT converts it directly into thioguanosine monophosphate, which is turned into thioguanine nucleotides. These are built into DNA and RNA and also inhibit purine synthesis and interconversion, so dividing cells stop and die. Thiopurine S-methyltransferase (TPMT) inactivates part of it, and people with inherited low enzyme activity accumulate toxic nucleotides.
- HGPRT converts tioguanine into thioguanosine monophosphate
- Thioguanine nucleotides form
- They are built into DNA and RNA and block purine synthesis
- Inherited low TPMT activity leads to toxic build-up
Indications
- Acute myeloid leukaemia, in combination regimens. Acute leukaemia (AML and ALL) →
Adverse effects
Common
- Nausea, vomiting, loss of appetite
- Mouth and throat sores
- Myelosuppression
- Headache
Contraindications
- Hypersensitivity to tioguanine or its ingredients
Key interactions
- Other myelosuppressive drugs
- Additive bone marrow suppression.
What is monitored
- Complete blood count regularly
- Liver tests and signs of liver injury (weight gain, abdominal swelling, jaundice)
- Genetic testing for a thiopurine risk factor before or during treatment, where available
Administration and safety
- Hazardous drug: tablets are handled with gloves.
- Generous fluid intake during treatment.
- Taken at about the same time every day, exactly on the prescribed schedule.
Pregnancy and breastfeeding
Can cause fetal harm; pregnancy and breastfeeding are avoided during treatment.
Nursing care
- Check counts and liver tests before each cycle.
- Weigh the patient and ask about abdominal swelling or right-sided pain.
- Teaching: report yellow skin or eyes, swelling, bleeding or fever at once.
Pharmacokinetics
- Absorption
- Oral tablets.
- Metabolism
- Activated by HGPRT; inactivated partly by TPMT methylation.
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme activates tioguanine?
HGPRT (hypoxanthine-guanine phosphoribosyltransferase).
Which leukaemia is tioguanine used for?
Acute myeloid leukaemia.
Which organ should be watched closely during tioguanine treatment?
The liver: jaundice, abdominal swelling and fluid retention signal damage.
Connections
← Back to the class: Antimetabolites
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Thioguanine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.