Entecavir: a potent new antiviral drug for hepatitis B.

Entecavir, a new deoxyguanine nucleoside analogue, is a selective inhibitor of the replication of the hepatitis B virus. In vitro this compound has proven to be far more effective than other nucleoside analogues. In animal models, an impressive reduction of serum viral DNA has been observed with covalently closed circular DNA and hepatitis B viral core antigen negativity in liver biopsy specimens. In clinical studies, entecavir revealed excellent suppression of hepatitis B virus replication without significant side effects or evidence of mitochondrial toxicity. Until now, no entecavir-resistant viral mutants have been described. Prolonged therapy as well as prophylactic therapy, for example, in liver transplant recipients, is feasible and not limited by breakthrough infections. Data on entecavir therapy for treatment of nucleoside-naive, wild-type hepatitis B virus is being generated in Phase III clinical trials worldwide for both hepatitis B envelope antigen-positive and -negative subpopulations, as well as in lamivudine-resistant patients. Based on mechanism and potency of interferon and entecavir, clinical trials with combination therapy are eagerly awaited.