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About Purixan™

Mercaptopurine1

Mercaptopurine is an integral component of ALL therapy.  Successive clinical trials have demonstrated that mercaptopurine contributes to successful maintenance therapy and improved survival of patients with ALL.  Mercaptopurine was originally approved as a 50 mg tablet in 1953, and since this approval has only been commercially available as a 50 mg tablet.

Because of the age and weight range of children with ALL, a 50 mg tablet is not ideal. Body surface area dosing and dose adjustments are not easily accomplished with the 50 mg tablet.  Tablets are not an ideal dosage form of medication for children less than 6 years.  Ad hoc local formulations compounded in pharmacies are commonly used. Alternatively 50 mg tablets are split to provide children with the desired dose.

Compared to tablets, a suspension offers the advantage of more accurately delivering the desired dose to children with a wide range of weights using a consistent administration schedule.  A suspension will allow more flexibility in adjusting the dose.  A commercially produced suspension is more likely to provide a more consistent dose of 6-mercaptopurine than ad hoc compounded formulations.

  1. Mulla H, Leary A, White P, Pandya H. A step toward more accurate dosing for mercaptopurine in childhood acute lymphoblastic leukemia. J Clin Pharmacol. 2012;52:1610-1613.
INDICATION

PURIXAN® is indicated for the treatment of patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen.

IMPORTANT SAFETY INFORMATION
Contraindications

None.

Warnings and Precautions

Myelosuppression

The most consistent, dose-related adverse reaction of PURIXAN is myelosuppression, manifested by anemia, leukopenia, thrombocytopenia, or any combination of these. Monitor CBC and adjust the dosage of PURIXAN for excessive myelosuppression.

Consider testing for thiopurine S-methyltransferase (TPMT) or nucleotide diphosphatase (NUDT15) deficiency in patients with severe myelosuppression or repeated episodes of myelosuppression. TPMT genotyping or phenotyping (red blood cell TPMT activity) and NUDT15 genotyping can identify patients who have reduced activity of these enzymes. Patients with homozygous TPMT or NUDT15 deficiency may require a dose reduction.

Myelosuppression can be exacerbated by coadministration with allopurinol, aminosalicylates or other products that cause myelosuppression. Reduce the dosage of PURIXAN when coadministered with allopurinol.

Hepatotoxicity

Mercaptopurine is hepatotoxic. There are reports of deaths attributed to hepatic necrosis associated with the administration of mercaptopurine. Hepatic injury can occur with any dosage but seems to occur with greater frequency when the recommended dosage is exceeded. In some patients, jaundice has cleared following withdrawal of mercaptopurine and reappeared with rechallenge.

Monitor serum transaminase levels, alkaline phosphatase, and bilirubin levels at weekly intervals when first beginning therapy and at monthly intervals thereafter. Monitor liver tests more frequently in patients who are receiving PURIXAN with other hepatotoxic drugs or with known pre-existing liver disease. Withhold PURIXAN at onset of hepatotoxicity.

Immunosuppression

Mercaptopurine is immunosuppressive and may impair the immune response to infectious agents or vaccines. Due to the immunosuppression associated with maintenance chemotherapy for ALL, response to all vaccines may be diminished and there is a risk of infection with live virus vaccines. Consult immunization guidelines for immunocompromised patients.

Treatment Related Malignancies

Patients receiving immunosuppressive therapy, including mercaptopurine, are at an increased risk of developing lymphoproliferative disorders and other malignancies, notably skin cancers (melanoma and non-melanoma), sarcomas (Kaposi's and non-Kaposi's) and uterine cervical cancer in situ. The increased risk appears to be related to the degree and duration of immunosuppression. It has been reported that discontinuation of immunosuppression may provide partial regression of the lymphoproliferative disorder.

A treatment regimen containing multiple immunosuppressants (including thiopurines) should therefore be used with caution as this could lead to lymphoproliferative disorders, some with reported fatalities. A combination of multiple immunosuppressants, given concomitantly increases the risk of Epstein-Barr virus (EBV)-associated lymphoproliferative disorders.

Macrophage Activation Syndrome

Macrophage activation syndrome (MAS) (hemophagocytic lymphohistiocytosis) is a known, life-threatening disorder that may develop in patients with autoimmune conditions, in particular with inflammatory bowel disease (IBD), and there could potentially be an increased susceptibility for developing the condition with the use of mercaptopurine (an unapproved use). If MAS occurs, or is suspected, discontinue PURIXAN. Monitor for and promptly treat infections such as EBV and cytomegalovirus (CMV), as these are known triggers for MAS.

Embryo-Fetal Toxicity

PURIXAN can cause fetal harm when administered to a pregnant woman. An increased incidence of miscarriage has been reported in women who received mercaptopurine in the first trimester of pregnancy. Adverse embryo-fetal findings, including miscarriage and stillbirth, have been reported in women who received mercaptopurine after the first trimester of pregnancy. Advise pregnant women of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment with PURIXAN and for 6 months after the last dose. Advise males with female partners of reproductive potential to use effective contraception during treatment with PURIXAN and for 3 months after the last dose.

Adverse Reactions

Based on multicenter cooperative group ALL trials, the most common adverse reaction occurring in > 20% of patients was myelosuppression, including anemia, neutropenia, lymphopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients included anorexia, nausea, vomiting, diarrhea, malaise, and rash. Adverse reactions occurring in 5% to 20% of patients included anorexia, nausea, vomiting, diarrhea, malaise, and rash. Adverse reactions occurring in < 5% of patients included urticaria, hyperuricemia, oral lesions, elevated transaminases, hyperbilirubinemia, hyperpigmentation, infections, and pancreatitis. Oral lesions resemble thrush rather than antifolic ulcerations. Delayed or late toxicities include hepatic fibrosis, hyperbilirubinemia, alopecia, pulmonary fibrosis, oligospermia and secondary malignancies.

USE IN SPECIFIC POPULATIONS
  • Lactation: Because of the potential for serious adverse reactions in the breastfed child, advise women not to breastfeed during treatment with PURIXAN and for 1 week after the last dose.
  • Pediatric Use: Symptomatic hypoglycemia has been reported in pediatric patients with ALL receiving mercaptopurine. Reported cases were in pediatrics less than 6 years or with a low body mass index.
  • Renal Impairment: Use the lowest recommended starting dosage for PURIXAN or increase the dosing interval to every 36 to 48 hours in patients with renal impairment (CLcr less than 50 mL/min). Adjust the dose to maintain absolute neutrophil count (ANC) at a desirable level and for adverse reactions.
  • Hepatic Impairment: Use the lowest recommended starting dosage for PURIXAN in patients with hepatic impairment. Adjust the dose to maintain absolute neutrophil count (ANC) at a desirable level and for adverse reactions.

 

OVERDOSAGE

Signs and symptoms of mercaptopurine overdosage may be immediate (anorexia, nausea, vomiting, and diarrhea) or delayed (myelosuppression, liver dysfunction, and gastroenteritis). Dialysis cannot be expected to clear mercaptopurine. Hemodialysis is thought to be of marginal use due to the rapid intracellular incorporation of mercaptopurine into active metabolites with long persistence.

Withhold PURIXAN immediately if severe or life-threatening adverse reactions occur during treatment. If a patient is seen immediately following an accidental overdosage, it may be useful to induce emesis.

 

Please see complete Prescribing Information.

To report SUSPECTED ADVERSE REACTIONS, contact Rare Disease Therapeutics, Inc., at 1-844-472-7389 or by email at safety@raretx.com, or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

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