Antibiotics May Not Be Needed After Abscess Incision and Drainage

Karla Gale, MS

April 9, 2010 — Antibiotics don't improve outcomes after incision and drainage of uncomplicated skin abscesses, new research indicates. They might prevent new abscesses at one month, however.

"We're seeing so many abscesses now," lead researcher Dr. Gillian R. Schmitz told Reuters Health. Before methicillin-resistant Staphylococcus aureus (MRSA) became so widespread, most abscess patients had diabetes or were immunocompromised, she said, "but now they're popping up all over the place in people with no traditional risk factors."

"But no one has studied best practice for treating abscesses," Dr. Schmitz added.

In a multicenter trial, she and her colleagues randomized 212 adults to receive trimethoprim-sulfamethoxazole (160 mg/800 mg) or placebo after incision and drainage of community-acquired abscesses. They instructed patients to take 2 pills twice daily for seven days. The primary outcome was treatment failure at 7 days, defined as no improvement after 2 days, development of a new separate abscess within 7 days, or worsening infection within 7 days requiring intervention.

Eighty-eight patients in the antibiotic group and 102 in the placebo group completed 7 days of follow-up; 46 and 50, respectively, returned at 30 days.

According to their March 29th online report in the Annals of Emergency Medicine, all bacterial isolates were uniformly sensitive to trimethoprim-sulfamethoxazole. Still, there was no significant difference in treatment failure rates at 7 days (17% in the antibiotic group and 26% in the placebo group, p = 0.12).

"Antibiotics don't help with resolution of infection," Dr. Schmitz said. "The most important thing is to open the wound, clean it, and get the pus out."

However, the total number of new lesions at 30 days was significantly lower in the antibiotic group: 9% vs 28% (p = 0.02).

"More study needs to be done to draw a conclusion about recurrence, because we lost so many to follow-up at 30 days," Dr. Schmitz said.

A separate trial in children with community-acquired skin abscesses found similar results. In a paper scheduled for print publication in the May issue of same journal, Dr. Myto Duong, currently at Southern Illinois University, Springfield, and associates report outcomes in 149 children after incision and drainage. The 73 children randomized to the intervention group took trimethoprim-sulfamethoxazole for 10 days (10-12 mg trimethoprim/kg/day in 2 divided doses, with a maximum of 160 mg per dose, in a liquid formulation containing 200 mg sulfamethoxazole/40 mg trimethoprim per 5 mL). The other 76 children received placebo.

The authors found no significant difference in failure rates at 10 days – 4.1% in the antibiotic group vs 5.3% in the placebo group. In addition, the antibiotic group had a significantly lower incidence of new lesions at day 10 (12.9%, vs 26.4% in the placebo group).

At 30 days, however, with 46 children in the antibiotics group and 52 in the placebo group evaluable, there was no longer a significant difference in the rate of new lesions (28.3% vs 28.8%, respectively).

"Antibiotics are not required for pediatric skin abscess resolution," Dr. Duong's group concludes, adding that further research is needed to see if antibiotics help prevent new lesions in the short term.

Both studies were limited by attrition of patients and by inclusion of subjects who were otherwise healthy, so the results can't be generalized to patients with comorbidities. In Dr. Duong's trial, medication compliance was only 66%.

In an editorial, Dr. David A. Talan of Olive View--UCLA Medical Center in Sylmar, California, states, "Antibiotics for drained simple abscesses are not required to meet the standard of care."

He told Reuters Health, "The rate of resolution of patient groups described in these studies is very high, so doctors can feel that the odds are on their side" if they forego antibiotic treatment, "and they can reassure patients there's a good chance that things will work out fine."

But, he continued, physicians should be aware of the tendency for abscesses to return, and they should advise patients to seek attention if new symptoms appear after first infection resolves.

Ann Emerg Med. Published online March 29, 2010.