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9 Cards in this Set
- Front
- Back
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What nucleoside inhibitor is widely used to treat Herpesvirus infections?
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Acyclovir is used to treat herpes simplex virus type-1(HSV-1), herpes simplex virus type-2(HSV-2) and varicella zoster virus(VZV)
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What is the mechanism of action of acyclovir?
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Acyclovir is a guanosine nucleoside analog that is phosphorylated by viral thymidine kinase.
After phosphorylation, it competes with deoxyguanosine triphosphate(dGTP) for binding to the viral DNA polymerase and thus prevents further elongation of the DNA. |
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How does acyclovir achieve its selectivity?
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Acyclovir is highly selective because it must be phosphorylated by a virally encoded thymidine kinase to become activated. Activated acyclovir also preferentially inhibits viral DNA polymerase.
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What is selective toxicity?
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The extent to which a drug can inhibit viral replication without damaging the host cell.
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Does acyclovir affect reccurrence of the herpesvirus after treatment?
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No. While it reduces recurrence during treatment, it does not affcet latency once treatment is stopped.
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How does acyclovir differ from ganciclovir in terms of its clinical use?
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Ganciclovir is similar to acyclovir as it is also a guanosine nucleoside analog but it is more active against cytomegalovirus(CMV).
It is activated by a phosphokinase encoded by CMV. It is used to treat the retinitis caused by CMV, in AIDS patients as well as other CMV infections. |
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What is the main nonnucleoside inhibitor of herpesvirus?
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Foscarnet
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What is the mechanism of action of foscarnet against herpesvirus?
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It is a pyrophosphate analogue. It binds at the pyrophosphate cleavage site of DNA polymerase and prevents removal of phosphate from the nucleoside triphosphate. This ultimately inhibits the extension of the DNA strand. Foscarnet also inhibits viral RNA polymerase.
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Does Foscarnet have to be activated by tyrosine kinase or other kinases?
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No. Foscarnet is active in vitro and does not require activation by a kinase. It is used in acyclovir resistant HSV or CMV will be sensitive to foscarnet because resistance may have developed from mutations in the kinase or DNA polymerase. Mutations in DNA polymerase may also confer resistance to foscarnet.
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