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Pfizer has announced the voluntary withdrawal from the US market of the drug Mylotarg ( Gemtuzumab ozogamicin ) for patients with acute myeloid leukemia ( AML ). The company took the action at the request of the FDA ( Food and Drug Administration ) after results from a recent clinical trial raised new concerns about the product’s safety and the drug failed to demonstrate clinical benefit to patients enrolled in trials.

Mylotarg was approved in May 2000 under the FDA’s accelerated approval program. This program allows the agency to approve a drug to treat serious diseases with an unmet medical need based on a surrogate endpoint – a laboratory measurement or a physical sign used as a substitute for a clinically meaningful endpoint that directly measures how a patient feels, functions, or survives.

Under accelerated approval, the company is required to conduct additional clinical trials after approval to confirm the drug’s benefit. If those trials fail to confirm clinical benefit to patients, or if the company does not pursue the required confirmatory trials with due diligence, the FDA can withdraw the drug from the market using expedited procedures.

Mylotarg was approved to treat patients ages 60 years and older with recurrent acute myeloid leukemia who were not considered candidates for other chemotherapy. The initial approval was based on the surrogate endpoint of response rate ( i.e., the percentage of patients whose leukemia decreased or disappeared in laboratory tests ), observed in 142 patients with acute myeloid leukemia across three clinical trials.

A confirmatory, post approval clinical trial was begun by Wyeth ( now Pfizer ) in 2004. The trial was designed to determine whether adding Mylotarg to standard chemotherapy demonstrated an improvement in clinical benefit ( survival time ) to patients with acute myeloid leukemia. The trial was stopped early when no improvement in clinical benefit was observed, and after a greater number of deaths occurred in the group of patients who received Mylotarg compared with those receiving chemotherapy alone.

At initial approval, Mylotarg was associated with a serious liver condition called veno-occlusive disease, which can be fatal. This rate has increased in the postmarket setting.

Source: FDA, 2010

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