Fenivir Cold Sore Cream is the fastest and most effective treatment for active and recurrent cold sores and is clinically proven to treat cold sores within 4 days. Fenivir (penciclovir) is superior to acyclovir and should be preferred as a topical treatment. This fast-acting and effective treatment significantly reduces the duration, noticeability, severity and pain of cold sores 2 days faster than acyclovir.