(Reuters) ? Slower tumor growth in kidney cancer patients taking Pfizer Inc's experimental drug, Inlyta, in a clinical trial was driven by a subset of patients who are rare in the United States, U.S. Food and Drug Administration researchers said.
In review documents released on Monday ahead of an expert advisory panel meeting on the drug, FDA staff expressed concern the Pfizer medicine appeared to work better in patients previously treated by cytokines that are rarely used in the United States, potentially limiting its appeal in the world's largest market.
U.S. kidney cancer patients are far more likely to be given Pfizer's Sutent as an initial treatment option rather than cytokines.
The FDA documents found the safety profile of Inlyta, clinically known as axitinib, to be similar to rival drugs. However, interim analysis of Pfizer's pivotal trial showed more overall deaths and more deaths related to treatment in patients who received Inlyta compared with those who took Nexavar, which is sold by Bayer AG and Onyx Pharmaceuticals Inc.
Inlyta, which inhibits certain receptors that can influence tumor growth and progression of cancer, is one of several new drugs Pfizer is banking on to help replace lost revenue from its top-selling cholesterol fighter, Lipitor, which began facing generic competition last week.
FDA staff said Pfizer's kidney cancer drug showed the same degree of liver enzyme elevation and potential for liver failure as some other drugs in its class, but had lower rates of skin related side effects and anemia than Nexavar.
About 61,000 Americans will be diagnosed with kidney cancer this year and one in five of them are expected to die from the disease, according to the American Cancer Society. Most often, this cancer occurs in people over 55 years old.
The drug is awaiting an approval decision in Europe for use in patients who failed to be helped by prior treatment.
In November 2010, Pfizer released results of a study showing axitinib significantly delayed the time before the disease progressed compared with Nexavar in previously treated patients with advanced kidney cancer.
The trial also found the Pfizer drug delayed progression of the disease by some 5.6 months in patients previously treated with cytokines, but only by 1.4 months in those initially treated with Sutent, known chemically as sunitinib.
A panel of FDA advisers will consider whether the discrepancy affects Inlyta's risk-benefit ratio.
The drug is also being tested in another late-stage trial for kidney cancer as both an initial treatment option and in previously treated patients. It is also being tested as a treatment for liver cancer.
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