Entecavir: A New Nucleoside Analog for the Treatment of Chronic Hepatitis B Infection

BACKGROUND: Chronic hepatitis B infection carries considerable risk for the development of cirrhosis and hepatocellular carcinoma. Treatment options are increasing but are limited to interferon alfa-2b, pegylated interferon alfa-2a, lamivudine, adefovir dipivoxil, and entecavir. Entecavir, a nucleoside analog, is the newest oral antiviral approved in the United States for treatment of chronic hepatitis B. OBJECTIVE: To review the available data for entecavir regarding its pharmacology, pharmacokinetics, safety, efficacy, and clinical use. METHODS: A MEDLINE, EMBASE, and Cochrane search of the English-language literature from January 1997-May 2006 was performed. Preapproval studies provided by the manufacturer and abstracts from recent scientific meetings on infectious disease and hepatology were also reviewed. RESULTS: Three phase III clinical trials representing more than 1600 subjects established the superior efficacy and equivalent safety of entecavir compared with lamivudine for treating patients who are hepatitis B early antigen (HBeAg) positive, HBeAg negative, or refractory to lamivudine. Entecavir resistance has not occurred in nucleoside-naïve patients but may develop in those who already possess lamivudine resistance mutations. CONCLUSION: Trial results, along with previously published response rates for adefovir dipivoxil and interferon monotherapy, make entecavir the preferred first-line treatment option for patients with chronic hepatitis B who are nucleoside naïve, HBeAg positive or negative, and have compensated liver disease. Both entecavir and adefovir dipivoxil maintain activity against hepatitis B virus in patients with chronic hepatitis B who are refractory to lamivudine, and both agents are reasonable first-line treatment options. Longer trials involving nucleoside-naïve, lamivudine-refractory patients are needed to determine entecavir's optimal treatment duration, long-term safety, and durability of response, including rate of resistance.