Thioguanine
2-Amino-6-mercaptopurine
Also known as: Tabloid · Lanvis · Tioguanina · NSC-752 · 6-thioguanine · 6-TG · 2-Amino-6-mercaptopurine · WR-1141
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This dose is based on body surface area (mg/m²). Convert body weight to body surface area before dosing.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acute lymphocytic and granulocytic leukemia | 40 mg/m2 PO once daily (q24 hours) for 4-5 days, then every 3rd day thereafter | PO | q24h initially, then q72h | 4-5 days initially, then ongoing | 🌎 NA |
| Acute myelogenous leukemias (Protocol 1 & 2) | 50 mg/m2 PO q24-48h | PO | q24-48h | Ongoing | 🌎 NA |
- Acute lymphocytic and granulocytic leukemia: Consultation with a veterinary oncologist is strongly recommended.
- Acute myelogenous leukemias (Protocol 1 & 2): Used as part of a protocol with Cytarabine (100 mg/m2 SC daily for 2-6 days) +/- Doxorubicin (10 mg/m2 IV once a week).
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acute lymphocytic and granulocytic leukemia | 25 mg/m2 PO once daily (q24 hours) for 1-5 days, then every 30 days thereafter as necessary | PO | q24h initially, then q30d | 1-5 days initially, then ongoing | 🌎 NA |
- Acute lymphocytic and granulocytic leukemia: Cats are particularly susceptible to hematologic effects.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Thioguanine (6-TG) is a purine antimetabolite antineoplastic agent used primarily as an adjunctive treatment for acute lymphocytic or granulocytic leukemia in dogs and cats.
Clinical Pearls:
- It is a cell-cycle phase-specific drug, acting primarily in the S-phase (DNA synthesis).
- While it shares extensive cross-resistance with mercaptopurine, its metabolism is distinct (it does not rely on xanthine oxidase for degradation), which alters its interaction profile compared to azathioprine or mercaptopurine.
- It has a very narrow therapeutic index and requires rigorous monitoring of hematologic parameters.
- Cats are particularly sensitive to its myelosuppressive effects.
Mechanism of action
Thioguanine acts as a false purine base.
- Intracellular Activation: It is converted by the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) → thioguanine monophosphate (TGMP).
- DNA/RNA Incorporation: TGMP is further phosphorylated into di- and tri-nucleotides, which are then incorporated into DNA and RNA.
- Cytotoxicity: The insertion of these fraudulent nucleotides disrupts normal nucleic acid synthesis and function, leading to DNA strand breaks and apoptosis.
- It also causes feedback inhibition of de novo purine synthesis, further starving the cancer cells of essential nucleotides.
Safety & warnings
Contraindications
- Hypersensitivity to thioguanine
- Pregnancy (Category D - teratogenic and mutagenic)
Adverse effects
- Nausea
- Anorexia
- Vomiting
- Diarrhea
- Bone marrow suppression (leukopenia, thrombocytopenia, anemia)
- Hepatotoxicity
- Pancreatitis
- Gastrointestinal ulceration (including oral ulcers)
- Dermatologic reactions
Precautions
Strict Chemotherapy Safety Precautions Apply
- Hepatic/Renal Impairment: Use with extreme caution; dosage adjustments may be necessary.
- Pre-existing Conditions: Caution in patients with pre-existing bone marrow depression, active infections, or a history of urate urinary stones.
- Species Sensitivity: Cats are highly susceptible to hematologic toxicity.
- Reproduction: Potentially mutagenic and teratogenic. Do not use in pregnant animals. Nursing mothers should use milk replacer.
- Handling: Personnel and owners should follow safe handling protocols for cytotoxic drugs.
Drug interactions
Increased risk of hepatotoxicity; use concurrently with caution.
Increased risk of severe infection due to additive immunosuppression.
Additive bone marrow depression; extreme caution required.
Increased risk of vaccine-induced infection or decreased vaccine efficacy; use with caution or avoid.
Monitoring
- Hemograms (including platelets) initially every 1-2 weeks, then every 1-2 months on maintenance. (Dose reduction of 25% recommended if WBC drops to 5,000-7,000 cells/mm3; discontinue if < 5,000 cells/mm3 until resolved)
- Liver function tests
- Serum amylase (if pancreatitis is suspected)
- Clinical efficacy (remission status)
Pharmacokinetics
Absorption
Variable and incomplete; in humans, only about 30% of an oral dose is absorbed.
Distribution
Distributes into the DNA and RNA of bone marrow (may require several doses). Does not readily enter the CNS. Crosses the placenta.
Metabolism
Rapidly metabolized primarily in the liver to a methylate derivative that is less active and less toxic than the parent compound.
Elimination
Metabolites are eliminated primarily in the urine.
Overdose
Toxicity from overdosage can manifest as acute (severe gastrointestinal effects like nausea, vomiting, diarrhea) or delayed (profound bone marrow depression, hepatotoxicity, severe gastroenteritis).
Treatment:
- If ingestion was recent, use standard protocols to empty the GI tract (emesis/gastric lavage followed by activated charcoal), keeping in mind the risks of handling cytotoxic emesis.
- Provide aggressive supportive care (IV fluids, broad-spectrum antibiotics if neutropenic, blood products if severely anemic or thrombocytopenic).
Available products
Formulations
- Tablets
Human-labeled
- Thioguanine Tablets: 40 mg (Tabloid)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets in tight containers at room temperature.
Client information
This medication is a powerful chemotherapy drug used to treat certain types of leukemia. Because it is a potent drug, it requires careful handling and close monitoring.
- Safe Handling: Wash your hands thoroughly after administering the medication. Do not break or crush the tablets. Pregnant women, nursing mothers, and immunocompromised individuals should avoid handling this drug or the pet's waste.
- Waste Management: Your pet's bodily fluids (urine, feces, vomit) may contain traces of the drug for a few days after administration. Wear gloves when cleaning up accidents and wash hands afterward.
- What to Watch For: Contact your veterinarian immediately if your pet shows signs of abnormal bleeding, bruising, severe loss of appetite, vomiting, diarrhea, yellowing of the eyes/gums (jaundice), or signs of infection (like fever or extreme lethargy).
- Appointments: Keep all scheduled appointments for blood tests. These are mandatory to ensure the drug is not damaging your pet's bone marrow or liver.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.