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Mercaptopurine: Indications, Dosing, Side Effects and Interactions
Mercaptopurine clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 4 min read
Mercaptopurine: Indications, Dosing, Side Effects and Interactions
Mercaptopurine clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Severe acute Crohn's disease (under expert supervision),Maintenance of remission of Crohn's disease (under expert supervision),Maintenance of remission of ulcerative colitis (under expert supervision)**
- **Adult** (By Mouth): Severe acute Crohn's disease (under expert supervision), Maintenance of remission of Crohn's disease (under expert supervision), Maintenance of remission of ulcerative colitis (under expert supervision) 1-1.5 mg/kg daily, some patients may respond to lower doses.
**Acute leukaemias (specialist use only),Chronic myeloid leukaemia (specialist use only)**
- **Adult** (By Mouth): Specialist indication - access specialist resources for dosing information.
**Severe ulcerative colitis (under expert supervision), Severe Crohn's disease (under expert supervision) for mercaptopurine**
- **Child 2-17 years** (By mouth): 1-1.5 mg/kg once daily, initial max. dose 50 mg once daily; may be increased if necessary up to max. 75 mg once daily.
**Acute lymphoblastic leukaemia (specialist use only), Lymphoblastic lymphomas (specialist use only) for mercaptopurine**
- **Child** (By mouth): Specialist indication - access specialist resources for dosing information.
Cautions
Reduced thiopurine methyltransferase activity Cautions, further information Thiopurine methyltransferase The enzyme thiopurine methyltransferase (TPMT) metabolises thiopurine drugs (azathioprine, mercaptopurine, tioguanine); the risk of myelosuppression is increased in patients with reduced activity of the enzyme, particularly for the few individuals in whom TPMT activity is undetectable. Those with reduced TPMT activity may be treated under specialist supervision.
Contraindications
When used for non-cancer indications Absent thiopurine methyltransferase activity
Side effects
Common or very common Anaemia; appetite decreased; bone marrow depression; diarrhoea; hepatic disorders; hepatotoxicity (more common at high doses); leucopenia; nausea; oral disorders; pancreatitis; thrombocytopenia; vomiting Uncommon Arthralgia; fever; increased risk of infection; neutropenia; rash Rare or very rare Alopecia; face oedema; intestinal ulcer; neoplasms; oligozoospermia Frequency not known Photosensitivity reaction
Interactions
**Severe interactions:**
- Severe myelosuppression has been reported following concomitant administration of a pro-drug of mercaptopurine monohydrate and ribavirin; therefore concomitant administration of ribavirin and...
**Other interactions (19):**
- The administration of mercaptopurine monohydrate with food may decrease systemic exposure slightly.
- Mercaptopurine monohydrate may be taken with food or on an empty stomach, but patients should standardise the method of administration to avoid large variability in exposure.
- The dose should not be taken with milk or dairy products since they contain xanthine oxidase, an enzyme which metabolises 6-mercaptopurine and might therefore lead to reduced plasma concentrations...
- Anticoagulants Inhibition of the anticoagulant effect of warfarin, when given with mercaptopurine monohydrate has been reported.
- Monitoring of the INR (International Normalised Ratio) value is recommended during concomitant administration with oral anticoagulants.
- Antiepileptics Cytotoxic agents may decrease the intestinal absorption of phenytoin.
Pregnancy
Important safety information For mercaptopurine Safe Practice Mercaptopurine has been confused with mercaptamine; care must be taken to ensure the correct drug is prescribed and dispensed. Risks of incorrect dosing of oral anti-cancer medicines See Cytotoxic drugs . MHRA/CHM advice: Thiopurines and intrahepatic cholestasis of pregnancy (May 2025) Intrahepatic cholestasis of pregnancy (ICP) has been reported in a small number of patients taking azathioprine or mercaptopurine. Due to similar metabolic pathways, the risk of ICP is considered applicable to all drugs in the thiopurine class, including tioguanine. Thiopurine-induced ICP usually occurs earlier in pregnancy than non-drug-induced ICP and may not respond to ursodeoxycholic acid, however, stopping or reducing the dose of the thiopurine may improve liver-function tests. Some case reports resulted in fetal death, therefore early diagnosis and discontinuation or dose reduction of the thiopurine may minimise adverse effects in the fetus. Healthcare professionals are advised to undertake a case-by-case assessment if ICP occurs and consider the risks versus benefits of stopping or continuing thiopurine treatment. Non-fasting serum-bile acids should be measured in patients with ICP to identify pregnancies at particular risk of spontaneous preterm birth ( 40 micromol/litre) or stillbirth ( 100 micromol/litre). Patients and carers should be advised to seek immediate medical attention if signs or symptoms of ICP occur.
Breast feeding
Discontinue breast-feeding.
Hepatic impairment
Manufacturer advises caution (risk of increased exposure). Dose adjustments Manufacturer advises consider dose reduction.
Renal impairment
Use with caution. M Dose adjustments Consider dose reduction. M
Medicinal forms
Tablet,Tablet,Suspension
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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