July 1997
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Extensive impetigo initially mistaken for tinea. |
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Impetigo accounts for 10% of all skin problems that physicians
see in children. |
SAN FRANCISCO — Mupirocin (Bactroban, SmithKline Beecham) is efficacious in eradicating nasal Staphylococcus aureus carriage as well as routine impetigo, according to the results of several studies highlighted here at the annual meeting of the American Academy of Dermatology.
"Mupirocin is a useful topical agent for patients with eczema who have recurrent staph infections," said Sheila Fallon-Friedlander, MD, a pediatric dermatologist at the University of California, San Diego School of Medicine and Children's Hospital.
Fallon-Friedlander noted that impetigo is the most common primary skin infection. In fact, "10% of all skin problems that physicians see for children relate to impetigo," she said. Furthermore, impetigo represents 1% of all pediatric visits.
The epidemiology of the disease has changed over the past decade. "Today, the vast majority of cases are secondary to S. aureus rather than strep," said Fallon-Friedlander. Secondarily infected eczema is on the rise, too.
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Moreover, there is an increasing incidence of erythromycin resistance, estimated at 10% to 40%, depending on where the patient lives and the frequency of treatment. Fallon-Friedlander noted that the erythromycin resistance rate in 1995 was 52% in Australia and 43% in Japan, compared with only 18% in San Diego this February.
From this data, clinicians might conclude that erythromycin should not be used in countries such as Australia and Japan.
"But you've got to remember that these are in vitro numbers. These are numbers for bacteria that have been tested in the laboratory," said Fallon-Friedlander. In reality, "we have found that in vitro is not always equivalent to in vivo." Patients often respond to the drug even when the organism is "resistant" by laboratory standards.
One recently published study by M. L. Misko et al in Pediatric Dermatology noted that patients with erythromycin-resistant organisms may still respond to the drug. Of 98 Texas patients with superficial skin infections, 87% grew S. aureus and 26% of S. aureus isolates were erythromycin resistant. However, there was only one treatment failure when erythromycin was used as therapy.
For localized impetigo, mupirocin ointment is a "wonderful treatment three times a day for seven days. For generalized or extensive disease, though, a systemic antibiotic is required," she said.
"I don't usually use erythromycin because of gastrointestinal [GI] problems," said Fallon-Friedlander. "Families tend to be noncompliant because of high incidence of stomachaches, nausea and vomiting. However, it is an inexpensive and generally effective drug — if you can get it in," she commented.
Consequently, she and most other practitioners advocate using a first-generation cephalosporin like keflex as the first line of therapy for extensive impetigo. "It is pleasant tasting and has few side effects. One does not usually encounter the GI side effects which are commonly seen with erythromycin."
However, first-generation cephalosporins have their drawbacks. "To get appropriate drug levels, it needs to be taken at least three times a day," explained Fallon-Friedlander. "There are practitioners, though, who use only twice-daily dosing. Most of the time this works, but pharmacokinetic studies indicate that at least three times a day is the more appropriate dosing regimen," she said.
Other drugs that are useful in the treatment of impetigo include semi-synthetic penicillins, such as dicloxacillin. However, "because it has an offensive taste, most children will not take it," warned Fallon-Friedlander.
Topical mupirocin can be used to prevent secondary bacterial infection in atopic dermatitis. Furthermore, mupirocin has been shown to eliminate nasal carriage of S. aureus "Some patients have recurrent impetigo or staph infections. In many cases, these people are colonized in the nares with S. aureus," she related.
If such patients are treated twice a day for five days with a local application of mupirocin to the nasal vestibules, "more than 98% of them will have staph eradicated from their nares," reported Fallon-Friedlander.
However, over time, staphylococci tends to recolonize, so "patients should be retreated at least every six months," said Fallon-Friedlander, noting that treatment is very easy. "You have a cotton swab that you place in the nasal vestibules, twice a day for five days. If you do that every six months, in most patients you will be able to eradicate staphylococcal carriage."
A study has documented mupirocin's ability to decrease the incidence of skin infections, as well as Staphylococcus carriage, in patients with recurring staph infections. "Patients who were chronic nasal S. aureus carriers and who applied the ointment twice daily to the nasal orifices, five days per month for six months, had a markedly decreased incidence of skin infections," reported Fallon-Friedlander.
Among the 34 study patients, there were 62 cases of skin infections among the control group, but only 26 cases for those treated with mupirocin ointment. Furthermore, eight patients remained culture negative in the treated group as compared with only two in the control group. "Of the eight mupirocin patients who cleared, none of them had skin infections during this time," she said.
Severe group A streptococcal infections are also on the rise. "We believe that group A b-hemolytic strep, which is causing these infections, has taken on new characteristics that make it more virulent," said Fallon-Friedlander.
Penicillin is the drug of choice for patients with severe invasive streptococcal disease. "It is now also believed that the addition of clindamycin may prove efficacious," said Fallon-Friedlander. "The addition of clindamycin may be beneficial because it inhibits protein production in bacteria, eradicating the toxin that is believed to act as a superantigen capable of stimulating a severe inflammatory reaction."
Fallon-Friedlander mentioned streptococcal toxic shock syndrome and necrotizing fasciitis, using the example of a small boy complaining of flank pain.
"The pediatrician carefully examined him and found an area of localized tenderness, but nothing else." The boy was sent home; however, 24 hours later he had spiking fevers and evolving blisters in the area, becoming hypotensive.
"These cases, although they are not receiving as much publicity, are still occurring," she said. Therefore, "if you have a child or any patient who comes in with localized symptoms that are remarkable and persistent, you need to counsel the families about careful monitoring and observation, because this disorder can present initially with very little in the way of findings and rapidly evolve."
For more information:
- Fallon-Friedlander S. Pediatric exanthems. Presented at the American Academy of Dermatology meeting. Mar. 21-26. San Francisco.
- Darmstadt GL. Oral antibiotic therapy for uncomplicated bacterial skin infections in children. Pediatr Infect Dis J.1997;16:227-40.
- Raz R et al. Mupirocin decreases skin infections as well as staphylococcus carriage. Arch Int Med.1996;156:1109-12.
Editor's note: The reason what appears to be resistant staph responds to erythromycin may relate to how long after onset the cultures are obtained. In a study done years ago, it was found that early cultures are more likely to yield strep; later cultures staph. Apparently there is overgrowth by staph in impetiginous lesions that were initially caused by strep. — P. Brunell
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