New cold sore cream on the market.

It's not a cure, but it's progress. For the one person in five who suffers from cold sores, researchers report that a new cream shortens by a day the time it takes for the painful lip lesions to heal.

In a study at six sites in the United States and the United Kingdom, half of 1,573 otherwise healthy patients smeared their cold sores every 2 hours with penciclovir, an antiviral cream. Compared to a placebo used by the other participants, the drug dispelled pain more quickly and rendered cold sores noninfectious sooner. The researchers report their findings in the May 7 Journal of the American Medical Association.

Most cold sores take 7 or 8 days to heal, but some can last 15 days. The sooner penciclovir was applied, the better it worked. In other studies, acyclovir, an ointment cousin of penciclovir, was inconsistent in speeding healing.

Both drugs block the virus' metabolism. "The difference is, penciclovir is retained inside the cell longer," which may make it more effective, says Spotswood Spruance, a coauthor of the study and professor of medicine at the University of Utah School of Medicine in Salt Lake City.

On the basis of this and another study, penciclovir has been cleared for prescription use in the United States.