Which of the following is used to treat cold sores?

Docosanol is an over-the-counter topical medication specifically used to treat cold sores, which are caused by the herpes simplex virus. It works by inhibiting the fusion of the virus to the host cell, therefore preventing the virus from entering and multiplying in the cells. This helps to shorten the duration of the cold sore outbreak and relieve symptoms at the earliest signs of a cold sore appearing.

While the other medications listed—Valacyclovir, Acyclovir, and Famciclovir—are antiviral medications that are effective in treating herpes simplex virus infections, they are typically used in different contexts, such as systemic infections and preventing recurrence of outbreaks. They require a prescription and are usually taken orally or through intravenous routes. Docosanol, being a topical option, allows for more direct treatment of the localized virus associated with cold sores.