Pfizer Inc. announced that based on discussions with the US Food and Drug Administration (FDA), it will be discontinuing commercial availability of Mylotarg (gemtuzumab ozogamicin for Injection) (used for the treatment of relapsed acute myeloid leukaemia (AML)) in the United States and that it will be voluntarily withdrawing the new drug application (NDA) for Mylotarg effective October 15, 2010.

The approval of single agent Mylotarg in the US was granted under FDA’s accelerated approval regulations based on overall response rate in three non-comparative studies and required submission of additional data to confirm clinical benefit. The required post-approval study (SWOG S0106) combining chemotherapy and Mylotarg did not demonstrate improved survival compared with chemotherapy alone in patients with previously untreated AML.

Additionally, among all patients evaluable for early toxicity the fatal induction toxicity rate was significantly higher in subjects given the combination of standard induction chemotherapy and Mylotarg than in those treated with chemotherapy alone.

After extensive discussions with the FDA, Pfizer has decided to withdraw the NDA effective October 15, 2010.

“We are disappointed that the study did not confirm the clinical benefit of Mylotarg. Our primary concern is for patients who suffer from AML, which remains a very serious and difficult-to treat disease with limited treatment options. We advise patients to contact their physicians for further information,” said Dr. Mace Rothenberg, senior vice president of clinical development and medical affairs for Pfizer Oncology Business Unit.

Patients who are currently taking Mylotarg and those patients who have been prescribed Mylotarg may continue their course of therapy, in consultation with their physicians. However, Pfizer recommends that no new patients in the US be prescribed Mylotarg. Future use of Mylotarg for new patients in the US will require physician submission of an Investigational New Drug (IND) application to the FDA.

The company is also working with Health Authorities outside the US and will keep patients, regulatory authorities, investigators and clinicians informed about FDA actions and appropriate next steps for Mylotarg.