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The Food and Drug Administration (FDA) has approved Tyzeka (telbivudine) for the treatment of adults with chronic hepatitis B (HBV), a serious viral infection that attacks the liver and can cause lifelong infection, scarring of the liver (cirrhosis), and eventually liver cancer, liver failure, and death. Tyzeka is a new molecular entity, which is a term used by the FDA to describe a medication containing an active substance that has never before been approved for marketing in any form in the United States.
"In a typical year, an estimated 70,000 Americans become infected with chronic HBV, and some 5,000 of them will die of the complications caused by the disease," said Dr. Steven Galson, director of the Center for Drug Evaluation and Research. "Tyzeka offers prescribers another option for treating these patients."
Tyzeka was studied in a year-long international clinical trial in 1,367 patients with chronic HBV. Three-quarters of the trial participants were male, and all were 16 years of age or older. The trial produced evidence of antiviral effectiveness, including the suppression of hepatitis B virus, and improvement in liver inflammation comparable to Epivir-HBV (lamivudine), one of five other medications approved to treat patients with chronic HBV.
HBV is spread when blood from an infected person enters the body of a person who is not infected, sometimes by sexual contact or blood contamination. Tyzeka is not a cure for hepatitis B, and long-term treatment benefits of this drug are not known. Use of Tyzeka has not been shown to reduce the risk of transmission of HBV to others through sexual contact or blood contamination.
In clinical studies Tyzeka was generally well tolerated, and most reported adverse events were mild to moderate. The most common side effects were elevated CPK (creatinine phosphokinase, an enzyme that is present in muscle tissue and is a marker for breakdown of muscle tissue), upper respiratory tract infection, fatigue, headache, abdominal pain and cough.
Also, after several weeks to months of Tyzeka use, some patients developed symptoms ranging from transient muscle pain to muscle weakness. Those who developed muscle weakness experienced significant improvement in their symptoms when Tyzeka was discontinued.
Patients should only stop Tyzeka after a careful discussion with their doctor. As has happened with other forms of treatment for hepatitis B, some patients who discontinued Tyzeka experienced a sudden and severe worsening of their hepatitis B. Therefore, patients who discontinue Tyzeka should be closely monitored by their doctor for at least several months.
Among drugs in the same class as Tyzeka, some cases of lactic acidosis (too much acid in the body due to buildup of lactic acid) and severe enlargement and accumulation of fat in the liver, including fatal cases, have been reported.
Tyzeka is manufactured by Novartis Pharma Stein AG, Stein, Switzerland and marketed and distributed by Idenix Pharmaceuticals, Inc. of Cambridge, Mass.