List of products in the National Drug Code with proprietary name . This medication is used to treat "cold sores/fever blisters" (herpes labialis). It can speed up healing of the sores and decrease symptoms (such as tingling, pain, burning, itching). Penciclovir belongs to a class of medications known as antivirals. It works by stopping the growth of the virus. This medication does not cure herpes, and it does not prevent passing the infection to someone else. It does not prevent future occurrences.