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The U.S. Food and Drug Administration (FDA) granted approval on Wednesday to Tyzeka™ (telbivudine), a new treatment for chronic hepatitis B virus (HBV) infection. While the new agent, developed by Switzerland's Novartis Pharma and being sold in the U.S. by Idenix Pharmaceuticals, has not been specifically approved for HIV-positive people with hepatitis B, it can still be prescribed by doctors treating patients with both infections.
The number of new hepatitis B infections in the U.S. has declined from about 260,000 a year in the 1980s to approximately 73,000 in 2003, with the greatest decline occurring in children and adolescents due to routine HBV vaccination. However, roughly 1.25 million people in the U.S. are living with chronic HBV infection, and 350 million are believed to be living with the virus worldwide.
Every year, approximately 5,000 people in the U.S. die of liver disease attributed to HBV infection in the U.S.
HBV is very similar to HIV in the ways it is transmitted, notably blood-to-blood contact and through sexual activity. In turn, many people living with HIV have also been exposed to HBV. What's more, HIV-positive people who are exposed to HBV are less likely to clear the infection within six months, ultimately leading to long-term (chronic) infection and an increased risk of severe liver damage and death.
Tyzeka was studied in a year-long international clinical trial involving 1,367 HIV-negative 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 HBV, and improvement in liver inflammation comparable to Epivir®.
Unlike other treatments active against HBV, such as Epivir, Hepsera®, Viread® (tenofovir), and Emtriva® (emtricitabine), Tyzeka does not have any activity against HIV. This is actually good news, as it might be used as a treatment for HBV before HIV treatment is needed. Tyzeka may be used as monotherapy in this situation without the risk of HIV becoming resistant to the drug and, as a result, becoming cross resistant to other nucleoside reverse transcriptase inhibitors (NRTIs) used to treat HIV infection.
In clinical studies, none of which included HIV-positive people, Tyzeka was generally well tolerated, and most reported adverse events were mild to moderate. The most common side effects were elevated CPK (creatinine phosphokinase, 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 muscle pain and muscle weakness. Those who developed these symptoms often experienced significant improvement after 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.
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