Which drug is commonly used to treat herpesvirus infections such as shingles and cold sores?

• A. Penicillin
• B. Azithromycin
• C. Ribavirin
• D. Acyclovir

Answer: (D)

Herpesvirus infections are treated with drugs that target viral DNA replication. Acyclovir is a guanine analogue that becomes active only after being phosphorylated by a virus-encoded thymidine kinase. Once activated, it inhibits viral DNA polymerase and acts as a chain terminator, meaning the viral DNA can't be correctly extended. This selective activation in infected cells makes acyclovir effective against HSV and VZV with relatively low toxicity to human cells. It’s used for cold sores (HSV-1) and shingles (varicella-zoster virus), and can be given orally, topically, or by IV depending on severity. The other options are antibiotics or antivirals not standard for herpesvirus infections, so acyclovir is the commonly used treatment.