tioguanine: clinical use

Prescribing considerations

• Restrict initiation and supervision to clinicians experienced with cytotoxic therapy.
• Long-term continuous or maintenance use is not recommended in the licensed oncology setting because of vascular liver toxicity.
• Review renal and hepatic function and consider TPMT and NUDT15 status before treatment; genetic testing does not replace blood-count monitoring.
• Plan for infection, tumour-lysis and marrow-aplasia risks within an appropriately supported treatment setting.

Contraindications and cautions

• Hypersensitivity to tioguanine or an excipient.
• The tablet contains lactose and is unsuitable for specified rare hereditary disorders of galactose or glucose-galactose handling.
• Use particular caution with hepatic or renal impairment, TPMT or NUDT15 variants, Lesch-Nyhan syndrome and concurrent myelotoxic treatment.

Monitoring

• Frequent full blood counts, recognising that counts may continue falling after treatment stops.
• Regular liver-function tests and assessment for jaundice, hepatomegaly, splenomegaly, fluid retention and portal hypertension.
• Renal function and uric acid where rapid cell breakdown is expected.
• Clinical surveillance for bacterial, viral and fungal infection.

Clinical pharmacology

Tioguanine is a guanine analogue activated through HPRT to thioguanine nucleotides. These inhibit purine synthesis and nucleotide interconversion and are incorporated into nucleic acids. TPMT, xanthine oxidase, aldehyde oxidase and other pathways contribute to its metabolism.

Formulation and product differences

• The UK-licensed product described is a scored oral tablet containing lactose.
• The score line is for easier swallowing and does not create equal portions.
• Some specialist paediatric services can supply a liquid preparation; licensing, storage, measurement and handling instructions may differ and must follow the dispensing pharmacy's label.

Tablet

Route: Oral

Strengths: 40 mg