FDA approves oral suspension of Purixan

The FDA recently approved a 20 mg/ml oral suspension of mercaptopurine, indicated for the treatment of patients with acute lymphoblastic leukemia as part of a combination regimen.

Successive clinical trials have demonstrated that mercaptopurine (Purixan, NOVA Laboratories Limited) contributes to successful maintenance therapy and improved survival of patients with ALL.

Originally approved as a 50 mg tablet in 1953, mercaptopurine has since only been commercially available in this dosage. However, due to 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. Additionally, tablets are not an ideal dosage form of medication for children less than 6 years.

In many cases, ad hoc local formulations compounded in pharmacies are frequently used or, alternatively, 50 mg tablets are split to provide children with the desired dose.

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

The approval was based on one clinical pharmacology study to assess the bioequivalence of mercaptopurine from Purinethol tablet with that of the mercaptopurine oral suspension in a healthy adult population.

The starting dose of mercaptopurine in multi-agent combination chemotherapy maintenance regimens is 1.5 to 2.5mg/kg (50 to 75 mg/m2) as a single daily dose. After initiating mercaptopurine, continuation of appropriate dosing requires periodic monitoring of absolute neutrophil count and platelet count to assure sufficient drug exposure (that is to maintain absolute neutrophil count at a desirable level) and to adjust for excessive hematological toxicity.