Famciclovir is an antiviral medicine which is used to treat
the following Herpes viruses:

• Herpes Simplex 1: Causes Oral Herpes also known
  as cold sores
• Herpes Simplex 2: Causes Genital Herpes
• Varicella Herpes Zoster: Causes chickenpox
  and shingles

Famciclovir is a prodrug of Penciclovir. Penciclovir is an
antiviral agent but as it absorbs poorly orally it is not very
efficient when used a an orally administered drug. Famciclovir
converts to Penciclovir which releases in the body after absorption
and then it is active against the Herpes virus. Penciclovir works by
inhibiting the reproduction of Herpes. When used as a preventive
treatment, it will help keep the virus latent and reduce shedding
of contagious virus. When used episodically it will reduce the severity,
duration and frequency of outbreaks.

Acyclovir was invented by Gertrude Elion and George Hutchings
who together received the Nobel Prize in 1988. Acyclovir has been
available for over a decade and the most common brand name is
Zovirax,
manufactured by GlaxoSmithKline

Valtrex is manufactured by
GlaxoSmithKline. It is an
antiviral treatment containing
Valacyclovir
used to treat Oral Herpes and Genital Herpes. It is a
a tablet and is available on prescription.