Valacyclovir

• also known to those who hate the letter 'y' (I know you're listening, Britain!) as valaciclovir
• trade name is Valtrex (see: Paris Hilton)
• is a prodrug, meaning that it is converted into acyclovir, the drug that actually does drug stuff, once it is absorbed into the body
• is active against both types of the herpes simplex virus (both can cause blistering of the mouth and/or genitals) and the varicella zoster virus (VZV, causes chickenpox when you first get infected with it, then it goes into hiding and is reactivated in some people in later life to produce herpes zoster, or shingles)
• doesn't curve these viral infections (there is no cure...mwahahahaha) but can reduce duration of symptoms and promote healing
• is a nucleoside analog, meaning that it mimics the basic components of DNA and RNA in order to mess with the replication and spread of the aforementioned viruses

Kalant H, Grant D, and Mitchell J. Principles of Medical Pharmacology 7th ed. Toronto: Saunders Canada, 2006.