WEDNESDAY, May 1 (HealthDay News) -- For people who have suffered from cellulitis of the leg, a long course of low-dose penicillin prevents the painful infection from returning, British researchers report.

Once the penicillin is stopped, however, its protective effect diminishes and the condition can flare up again, the researchers noted.

"Low-dose penicillin substantially reduces the risk of further episodes of leg cellulitis in those who have had two or more previous episodes," said lead researcher Hywel Williams, a professor of dermato-epidemiology at the University of Nottingham.

"The penicillin reduced recurrences from 37 percent in the group taking placebo to 22 percent in those taking penicillin," Williams said. "But this effect only occurred in the period that folks took the penicillin. When they stopped the 12 months of penicillin, the protective effect wore off."

Cellulitis is a common infection of the skin and deep underlying tissues. The two most common causes are Staphylococcus (staph) bacteria and group A strep. The bacteria enter the body through an injury such as a bruise, burn, surgical cut or wound, as well as through athlete's foot.

Symptoms can include fever and chills, swollen glands or lymph nodes, and a rash with painful, red, tender skin. In addition, the skin may blister and scab over.

The usual treatment is antibiotics, but the condition commonly returns when treatment is stopped.

Doctors and their patients now have reliable information on a possible way of reducing recurrences of this disabling and painful recurrent disease, Williams said.

"We now know for the first time that low-dose penicillin works, but we don't know how long it should be taken for and whether giving long-term antibiotics may cause resistance problems in the community in the long term, or whether it should be given for people with a first episode of cellulitis or just those with two or more previous episodes," he said.

The report was published in the May 2 issue of the New England Journal of Medicine.

One expert doesn't think this treatment is anything new.

"I know keeping you on antibiotics will prevent cellulitis from recurring," said Dr. Michele Green, a dermatologist at Lenox Hill Hospital, in New York City. "The problem is that the protective effect diminishes once drug therapy is stopped.

"This is what I do with older people. I keep them on antibiotics for a longer period of time so that they don't have a problem, but once you take them off they're just as vulnerable as they were before," Green said. "That's just common sense."

In addition, Green worries that keeping people on antibiotics for extended periods helps build the bacteria's resistance to the drug.

For the new study, Williams' team randomly assigned 274 people who had suffered from cellulitis of the leg that had been treated to one year of treatment with low-dose penicillin or placebos.

Over three years of follow-up, people taking penicillin saw a recurrence of cellulitis 626 days after the drug was stopped, compared with 532 days for those in the placebo group, the researchers found.

While on penicillin, 30 people had a recurrence of cellulitis, compared with 51 patients taking the placebo, they found.

More information

To find out more about cellulitis, visit the U.S. National Library of Medicine.