Pfizer to Withdraw AML Drug Following Disappointing Postapproval Trial Results

Study suggests that therapy leads to higher fatal induction toxicity rates.

Pfizer has confirmed it is voluntarily withdrawing the leukemia drug Mylotarg® from sale in the U.S. and will also withdraw the product’s NDA from October 15.

Mylotarg was originally granted FDA clearance as a single agent for the treatment of relapsed acute myeloid leukemia (AML) in older patients back in 2000 under the agency’s accelerated approval procedure. Marketing clearance was based on overall response rates from three noncomparative studies, but the agency also requested additional data to confirm the drug’s clinical benefit.

Pfizer says this Phase III post-approval study has now shown that adding Mylotarg to chemotherapy has no overall survival benefit for patients with previously untreated AML. The SWOG SO106 trial also showed that among patients evaluable for early toxicity, those receiving Mylotarg in addition to chemotherapy demonstrated a significantly higher fatal induction toxicity rate than patients receiving just chemotherapy.

“We are disappointed that the study did not confirm the clinical benefit of Mylotarg,” admits Mace Rothenberg, M.D., svp of clinical development and medical affairs for Pfizer’s oncology business unit. The firm does note that although SWOG SO106 did not show any benefit of adding Mylotarg to chemotherapy, the results do not directly impact the risk-benefit profile of the drug in its approved indication as a single agent.

Patients currently taking Mylotarg and those who have been prescribed the drug are being advised that they can continue their therapy in consultation with physicians. However, Pfizer is recommending that no new patients in the U.S. should be prescribed the drug, and future use of the treatment for new patients will require physician submission of an IND application to FDA.