Drug of choice for herpes zoster is: March 2010
**Core Concept**
Herpes zoster, also known as shingles, is a viral infection caused by the reactivation of varicella-zoster virus (VZV), which is the same virus that causes chickenpox. The drug of choice for herpes zoster is an antiviral medication that can help reduce the severity and duration of the illness.
**Why the Correct Answer is Right**
The drug of choice for herpes zoster is acyclovir, an antiviral medication that selectively inhibits viral DNA replication. Acyclovir works by competing with the viral nucleoside, guanosine, for incorporation into viral DNA, thereby inhibiting viral replication. It is most effective when started within 72 hours of the onset of rash.
**Why Each Wrong Option is Incorrect**
**Option A:** Penciclovir is another antiviral medication, but it is not the first-line treatment for herpes zoster. While it has a similar mechanism of action to acyclovir, it is less effective and more expensive.
**Option B:** Famciclovir is an antiviral medication that is used to treat herpes zoster, but it is not the drug of choice. It is a prodrug of penciclovir and is converted to its active form in the body.
**Option C:** Valacyclovir is an antiviral medication that is used to treat herpes simplex virus (HSV) infections, but it is not the drug of choice for herpes zoster. It is a prodrug of acyclovir and is converted to its active form in the body.
**Clinical Pearl / High-Yield Fact**
The Centers for Disease Control and Prevention (CDC) recommends that antiviral medications be started within 72 hours of the onset of rash to reduce the risk of complications and improve outcomes.
**Correct Answer:** A. Acyclovir.