Thioguanine (6-TG) — Drug Monograph

Brand names: Tabloid

Drug class: Antimetabolite

Mechanism of Action

A purine (guanine) analog thiopurine. Converted by HGPRT to thioguanine nucleotides that incorporate into DNA and RNA and inhibit purine biosynthesis and interconversion, producing cytotoxicity in proliferating leukemic cells. Unlike mercaptopurine, its activation does not depend on xanthine oxidase, so it lacks the clinically significant allopurinol dose-reduction requirement. Metabolized in part by TPMT.

FDA Indications

• Acute myeloid leukemia (AML) — remission induction and consolidation, generally in combination regimens

Common Side Effects

• Myelosuppression
• Nausea
• Vomiting
• Anorexia
• Stomatitis
• Diarrhea
• Elevated liver enzymes

Clinical Pearl

Unlike 6-mercaptopurine, thioguanine does not require a dose reduction with allopurinol because its activation is independent of xanthine oxidase. However, 6-TG carries a distinctive risk of hepatic veno-occlusive disease and nodular regenerative hyperplasia, so it is used for AML induction/consolidation rather than long-term maintenance.

Related Therapies & Mechanisms

• 5-Fluorouracil (5-FU) (Adrucil) — Antimetabolite
• Azacitidine (Vidaza) — Antimetabolite
• Capecitabine (Xeloda) — Antimetabolite
• Cladribine (Leustatin) — Antimetabolite