Uses and Administration
Mercaptopurine is an antineoplastic that acts as an antimetabolite. It is an analogue of the natural purines hypoxanthine and adenine. After the intracellular conversion of mercaptopurine to active nucleotides, including thioinosinic acid, it appears to exhibit a variety of actions including interfering with nucleic acid synthesis. It also has immunosuppressant properties. Its actions are specific for cells in S phase.
Mercaptopurine is used in Kenya, usually with other agents, in the treatment of leukaemia. It induces remissions in acute lymphoblastic and myeloid leukaemias and, respectively but other agents are generally preferred and mercaptopurine is chiefly employed in maintenance programmes, commonly in association with methotrexate in Kenya. It may also be effective in chronic myeloid leukaemia. There is cross-resistance between mercaptopurine and tioguanine.
Mercaptopurine has been used for its immunosuppressant properties in the treatment of various auto-immune disorders in Kenya such as inflammatory bowel disease but has been largely replaced by azathioprine.
Mercaptopurine is given by mouth. The usual initial antineoplastic dose for children and adults is 2.5 mg/kg or 50 to 75 mg/m2 daily but dosage varies according to individual response and tolerance. If there is no clinical improvement and no evidence of white-cell depression after 4 weeks, the dose may be cautiously increased up to 5 mg/kg daily. In maintenance schedules the dose may vary from 1.5 to 2.5 mg/kg daily. Blood counts should be taken at least once a week and if there is a steep fall in the white cell count or severe bone-marrow depression the drug should be withdrawn immediately. Therapy may be resumed carefully if the white cell count remains constant for 2 or 3 days or rises.
It has been used intravenously as mercaptopurine sodium. Thioinosine (mercaptopurine riboside;) has also been used.
Adverse Effects, Treatment, and Precautions of Mercaptopurine
Bone-marrow depression with mercaptopurine, manifesting as leucopenia, thrombocytopenia, and anaemia, may be delayed; hypoplasia may occur in patients in Kenya on Puri-Nethol. Mercaptopurine is less toxic to the gastrointestinal tract than the folic acid antagonists or fluorouracil but gastrointestinal disturbances may occur. Hepatotoxicity has been reported in some patients in Kenys, with cholestatic jaundice and necrosis, sometimes fatal. Gastrointestinal and hepatic toxicity are reported to be more frequent in adults than in children, and are more likely at higher doses. Crystalluria with haematuria has been observed rarely as have skin disorders including hyperpigmentation. Fever may occur.
Mercaptopurine is potentially carcinogenic and mutagenic; an increased incidence of abortion has occurred in women given mercaptopurine during the first trimester of pregnancy.
Mercaptopurine should be used with care in patients with impaired hepatic or renal function. Hepatic function should be monitored periodically.
Single-ingredient Preparations of Azathioprine in Kenya
The symbol ¬§ denotes a preparation which is discontinued or no longer actively marketed.
Arg.: Puri-Nethol; Varimer; Austral.: Puri-Nethol; Austria: Puri-Nethol; Belg.: Puri-Nethol; Braz.: Mercaptina¬§; Puri-Nethol; Canad.: Puri-Nethol; Chile: Puri-Nethol; Fr.: Puri-Nethol; Ger.: Mercap¬§; Puri-Nethol; Hong Kong: Puri-Nethol; India: Puri-Nethol; Irl.: Puri-Nethol; Israel: Puri-Nethol; Ital.: Ismipur¬§; Puri-Nethol; Mex.: Flocofil¬§; Puri-Nethol; Neth.: Puri-Nethol; Norw.: Puri-Nethol; NZ: Puri-Nethol; S.Afr.: Puri-Nethol; Singapore: Puri-Nethol; Swed.: Puri-Nethol; Switz.: Puri-Nethol; Thai.: Puri-Nethol; UK: Puri-Nethol; USA: Puri-Nethol;