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Pfizer's Mylotarg receives Orphan Drug Designation from FDA

Pfizer's acute myeloid leukemia (AML) medicine Mylotarg (gemtuzumab, ozogamicin) has been granted Orphan Drug Designation by the US Food and Drug Administration (FDA). The drug is indicated for the treatment of adults with newly diagnosed AML whose tumors express the CD33 antigen (CD33-positive AML), and for patients over the age of two with CD-33 positive AML who have relapsed or failed to respond to initial treatment. Orphan Drug Designation provides incentives to pharmaceutical firms to promote and encourage further development of medical products to treat relatively rare diseases and conditions.

Mylotarg is a targeted therapy containing an antibody connected to an anti-tumor agent and it is thought to work by blocking the growth of cancerous cells by targeting the AML cells expressing the CD33 antigen. The drug comes as an injection for IV infusion, with 4.5mg single-dose vials. It is the only AML therapy to target the CD33 antigen, which is expressed on AML cells in nine out of ten patients, according to Pfizer. 

Pfizer's medication first gained accelerated approval in 2000 and was the first antibody drug conjugate approved by the FDA. However, in June 2010, the pharmaceutical giant withdrew the drug from the market at the request of the FDA, following clinical trials which demonstrated safety concerns, and failed to verify the clinical benefits of the drug. The latest FDA approval of Mylotarg is for a lower dosage, different schedule and different group of patients.

The FDA's latest approval of Mylotarg was granted after two clinical trials demonstrated the safety and efficacy of the medication. The first trial showed patients receiving Mylotarg lived longer than those receiving only supportive care, while the second measured how many patients achieved complete remission. It found more than one-quarter of participants achieved a complete remission, which lasted for a median of almost one year. 

"Mylotarg's history underscores the importance of examining alternative dosing, scheduling, and administration of therapies for patients with cancer, especially in those who may be most vulnerable to the side effects of treatment," stated Richard Pazdur, MD, director of the FDA's Oncology Center of Excellence and acting director of the Office of Hematology and Oncology Products in the FDA's Center for Drug Evaluation and Research.

Common Side Effects of Mylotarg

  • Fever
  • Bleeding
  • Infection
  • Nausea
  • Vomiting
  • Constipation
  • Rash
  • Headache
  • Mouth sores
  • Increase in lab tests measuring liver function. 
  • The prescribing information also warns that some patients experienced severe liver damage while taking Mylotarg.

Patients should consult with their doctors for further advice about adverse events. Breastfeeding mothers and pregnant women should not take Mylotarg as it could harm a developing fetus or newborn baby. 

More than 62,000 new cases of leukemia are expected to be diagnosed in the US this year, according to figures from the American Cancer Society. It estimates there will be around 21,380 new cases of AML and that the disease will result in more than 10,000 deaths across the country. The condition is a rapidly progressing form of cancer that develops in the bone marrow and affects the white blood cells. Drugs used to treat AML include Cytarabine (cytarabine), Vincasar Pfs (vincristine) and Cerubidine (daunorubicin).

For more information on Mylotarg, visit