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What is All of the following drugs have activity against hepatitis B virus EXCEPT: and explain in detail?
Lamivudine (3TC) :This deoxycytidine analogue IS phosphorylated intracellularly and inhibits HIV reverse transcriptase as well as hepatitis B virus (HBV) DNA polymerase. Zidovudine: It is a thymidine analogue (azidothymidine, AZT), the prototype NI. After phosphorylation in the host cell-zidovudine triphosphate selectively inhibits viral reverse transcriptase (RNA-dependent DNA polymerase) in preference to cellular DNA polymerase. Zidovudine is used in HIV infected patients only in combination with at least 2 other ARV drugs. However, its efficacy as monotherapy in AIDS has been confirmed in the past. HIV-RNA titer is reduced to undetectable levels and CD4 count increases progressively. Emtricitabine:It exhibits clinical activity against the HBV. Among individuals with chronic HBV infection, emtricitabine treatment results in significant histologic, virologic, and biochemical improvement. The safety profile of emtricitabine during treatment is similar to that of a placebo. Telbivudine is an antiviral used in the treatment of hepatitis B infection.Telbivudine impairs hepatitis B virus (HBV) DNA replication by leading to chain termination. It differs from the natural nucleotide only with respect to the location of the sugar and base moieties, taking on an levorotatory configuration versus a dextrorotatory configuration as do the natural deoxynucleosides. It is taken orally in a dose of 600 mg once daily with or without food. ESSENTIALS OF MEDICAL PHARMACOLOGY,en.wikipedia.org K.D.TRIPATHI SIXTH EDITION PAGE NO:770,771