Famciclovir: An overview
- Kimon C Zachary, MD
Kimon C Zachary, MD
- Assistant Professor of Medicine
- Harvard Medical School
Famciclovir is an oral prodrug that is converted by first-pass metabolism to the antiviral drug penciclovir [1,2].
MECHANISM OF ACTION
Penciclovir, upon intracellular uptake, is monophosphorylated by virally-encoded thymidine kinase and subsequently converted to a triphosphate by cellular enzymes. Penciclovir triphosphate preferentially inhibits the DNA polymerase of susceptible viruses; at clinically relevant levels, there is no substantial effect upon cellular DNA polymerase, thereby minimizing side effects to the host .
This mechanism is similar to that described for acyclovir; however, compared with acyclovir triphosphate, penciclovir triphosphate has a lower affinity for viral DNA polymerase but a longer intracellular half-life . (See "Acyclovir: An overview".)
Spectrum of activity — Penciclovir is active against herpes simplex virus (HSV) types 1 and 2, and varicella zoster virus (VZV). Epstein-Barr virus is also susceptible in vitro .
Mechanism of resistance — The mechanisms of resistance to penciclovir are similar to those described for acyclovir . Three mechanisms have been shown to endow herpes simplex viruses with resistance to acyclovir, a phenomenon rare in the immunocompetent host :
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