mercaptopurine

Absorption: Variably and incompletely (5–50%) absorbed after oral administration.

Distribution: Widely distributed to tissues.

Metabolism/Excretion: Metabolized by liver. Converted to inactive metabolite by thiopurine methyltransferase (TPMT); nucleotide diphosphatase [NUDT15] is also involved in inactivation process. Nearly 50% is excreted unchanged by the kidneys.

Half-Life: 1.3 hr.

Time/Action Profile ⬆ ⬇

(effects on blood counts)

ROUTE	ONSET	PEAK	DURATION
PO	7–10 days	14 days	21 days

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
Severe hepatic impairment;
OB: Pregnancy;
Lactation: Lactation.

Use Cautiously in:

Infection;
↓bone marrow reserve;
Patients with homozygous TPMT enzyme deficiency or NUDT15 deficiency (substantial dose ↓ are required to avoid hematologic adverse events);
Rep: Women of reproductive potential;
Geri: Older adults have risk of adverse reactions.

Adv. Reactions/Side Effects ⬆ ⬇

Derm: alopecia, hyperpigmentation

Endo: gonadal suppression

GI: anorexia, diarrhea, HEPATOSPLENIC T-CELL LYMPHOMA, HEPATOTOXICITY, nausea, vomiting

GU: oligospermia

Hemat: anemia, leukopenia, thrombocytopenia, MACROPHAGE ACTIVATION SYNDROME

Metab: hyperuricemia

Neuro: weakness

Misc: fever, SECONDARY MALIGNANCY

Interactions ⬆ ⬇

Drug-drug:

Allopurinol may ↑ risk of toxicity (↓ dose of mercaptopurine to 25–33% of the usual dose).
A similar effect may occur with olsalazine, sulfasalazine, and mesalamine.
May ↑ risk of bleeding with warfarin.
↑risk of hepatotoxicity with other hepatotoxic agents.
↑bone marrow depression with trimethoprim/sulfamethoxazole, other antineoplastics, or radiation therapy.
May alter the effect of warfarin.
↓antibody response to live-virus vaccines and ↑ risk of adverse reactions.

Drug-Natural Products:

Concomitant use with echinacea and melatonin may interfere with immunosuppression.

Route/Dosage ⬆ ⬇

PO (Adults ): 1.5–2.5 mg/kg/day as a single dose.
PO (Children ): 2.5 mg/kg/day (75 mg/m²) single dose or divided doses (dose should be rounded to the nearest 25 mg).

Availability ⬆ ⬇

(Generic available)

Tablets: 50 mg
Oral suspension raspberry flavor: 20 mg/mL

Assessment ⬆ ⬇

Monitor BP, HR, respiratory rate, and temperature frequently during therapy. Report significant changes.
Monitor for bone marrow depression. Assess for bleeding (bleeding gums, bruising, petechiae; guaiac stools, urine, and emesis) and avoid IM injections and rectal temperatures if platelet count is low. Apply pressure to venipuncture sites for 10 min. Assess for signs of infection during neutropenia. Anemia may occur. Monitor for ↑ fatigue, dyspnea, and orthostatic hypotension. If severe myelosuppression occurs, consider testing for genetic metabolic abnormality.
Monitor intake and output ratios and inform health care professional if significant discrepancies occur. Encourage fluid intake of 2000–3000 mL/day. Allopurinol and alkalinization of the urine may be used to ↓ serum uric acid levels and to help prevent urate stone formation.
Assess patient’s nutritional status. Anorexia and weight loss can be ↓ by feeding light, frequent meals. Nausea and vomiting can be minimized by administering an antiemetic ≥1 hr before receiving medication.

Lab Test Considerations:

Verify negative pregnancy test before starting therapy.
- Monitor CBC and differential before and weekly during therapy. May cause leukopenia, thrombocytopenia, and anemia. Notify health care professional if a sudden drop in values occurs. Leukopenia and thrombocytopenia are usually mild, occur 5–6 days after initiation of therapy, and persist for approximately 7 days after discontinuation of therapy.
- Evaluate TPMT and NUDT15 status in patients with severe myelosuppression or repeated episodes of myelosuppression. In patients with homozygous deficiency, may ↓ dose by ≥10% of recommended dose. ↓ starting dose in patients with known deficiency. In patients with heterozygous deficiency,↓ dose based on tolerability. Most patients with deficiency tolerate recommended dose, but may require dose ↓ based on adverse reactions. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose ↓.
- Monitor hepatic function (AST, ALT, alkaline phosphatase, LDH, bilirubin) weekly during early therapy and monthly thereafter. Hepatotoxicity has occurred between 1 wk and 8 yr of dosing.
- Monitor renal function (BUN, serum creatinine) and serum uric acid concentrations before and periodically during therapy. May cause ↑ uric acid.
- Serum glucose and uric acid levels may show false ↑ when sequential multiple analyzer is used to determine values.

Implementation ⬆ ⬇

Fatalities have occurred with chemotherapeutic agents. Before administering, clarify all ambiguous orders; double-check single, daily, and course-of-therapy dose limits; have second practitioner independently double-check original order and dose calculations.
PO: Administer medication with meals. Tablets may be crushed if patient has difficulty swallowing.
- Shake suspension for ≥30 sec to make sure well mixed; suspension is pink to brown and viscous. Use oral syringe for accurate dose; wash and dry syringe between doses. Stable for 6 wk after opening.

Patient/Family Teaching ⬆ ⬇

Explain purpose and side effects of medication to patient. Advise patient to read Patient Information before starting therapy. Emphasize the need for periodic lab tests to monitor for side effects. Take as directed. If dose is missed, take dose as scheduled; do not double dose.
Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult health care professional before taking other medications.
Instruct patient to notify health care professional promptly if fever; chills; cough; hoarseness; sore throat; signs of infection; lower back or side pain; painful or difficult urination; bleeding gums; bruising; petechiae; blood in stools, urine, or emesis; ↑ fatigue; dyspnea; or orthostatic hypotension occur. Caution patient to avoid crowds and persons with known infections. Instruct patient to use soft toothbrush and electric razor and to avoid falls. Caution patient not to drink alcoholic beverages or take medication containing aspirin or NSAIDs; may precipitate gastric bleeding.
Instruct patient to report yellowing of skin or eyes, anorexia, diarrhea, jaundice, ascites, dark-colored urine, clay-colored stools, abdominal pain, flank or joint pain, or swelling of feet or legs to health care professional promptly.
Instruct patient not to receive any vaccinations without advice of health care professional.
Rep: May cause fetal harm. Advise females of reproductive potential to use effective contraception during therapy and for 6 mo after last dose and to avoid breastfeeding during and for 1 wk after last dose of therapy. Advise males with female partners of reproductive potential to use effective contraception during and for 3 mo after last dose. May impair male and female fertility. May cause intrahepatic cholestasis of pregnancy (ICP) when used for inflammatory bowel disease. Discontinue therapy if ICP develops during pregnancy.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇