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Thiopurine Immunomodulator

Mercaptopurine (6-MP)

Brand names: Xaluprine

Mercaptopurine (6-MP) is a thiopurine used in inflammatory bowel disease (often as an azathioprine alternative) and in leukaemia.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

• The recommended starting dosage of mercaptopurine oral suspension is 1.5 mg/kg to 2.5 mg/kg (50 mg/m 2 to 75 mg/m 2 ) orally once daily as part of a combination chemotherapy maintenance regimen. Adjust dose to maintain desirable absolute neutrophil count and for excessive myelosuppression. ( 2.1 ) • Renal Impairment : Use the lowest recommended starting dose or increase the dosing interval. ( 2.3 , 8.6 ) • Hepatic Impairment : Use the lowest recommended starting dose. ( 2.3 , 8.7 ) 2.1 Recommended Dosage The recommended starting dose of mercaptopurine oral suspension is 1.5 mg/kg to 2.5 mg/kg (50 mg/m 2 to 75 mg/m 2 ) orally once daily as part of combination chemotherapy maintenance …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-04-04. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

A purine analogue (and the active metabolite of azathioprine) that impairs DNA synthesis and lymphocyte proliferation.

Prescribing in practice

  • Check TPMT activity before starting — low activity greatly raises the risk of bone-marrow suppression.
  • Myelosuppression, hepatotoxicity and pancreatitis occur; there is increased infection and malignancy risk.
  • It interacts dangerously with allopurinol and febuxostat (greatly increased toxicity) — major dose reduction or avoidance is required.

Monitoring

Check TPMT before starting; monitor FBC and liver function regularly.

Counselling the patient

  • Attend all your blood tests.
  • Report a sore throat, fever, bruising or yellowing of the skin/eyes.
  • Tell clinicians you take it before starting allopurinol for gout.

Evidence & guidelines

A thiopurine immunosuppressant for IBD and leukaemia, requiring TPMT testing and blood monitoring (mirrors azathioprine).

Reference: ECCO IBD Guidelines 2021; MHRA Drug Safety Update on TPMT; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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