Options for Treating Skin Infections in the CA-MRSA Era

HONOLULU – For community-acquired methicillin-resistant Staphylococcus aureus infections of the face, cephalexin should rarely be the antibiotic of choice, according to a decision analysis performed by researchers at the University of California, San Francisco, and presented at the annual meeting of the Pediatric Academic Societies.

A second study, this one from Cardinal Glennon Children's Medical Center in St. Louis, called into question whether an antibiotic is needed at all to treat a primary skin infection if abscesses are incised and drained.

In the San Francisco study, Dr. Adam Hersh and associates from the university weighed the tradeoffs associated with three antibiotic choices–cephalexin, trimethoprim/sulfamethoxazole, or clindamycin–for empiric treatment of a purulent skin infection in a child under the age of 18.

Cephalexin does not treat CA-MRSA; trimethoprim/sulfamethoxazole does not treat group A Streptococcus; while clindamycin treats both, CA-MRSA is becoming increasingly resistant to it in some communities, said Dr. Hersh.

When community physicians consistently culture skin infections and prevalence and resistance rates can be developed, a decision tree analysis can be a method of “exquisitely weighing the tradeoffs between treatment choices,” he commented.

In communities that now have a prevalence of CA-MRSA of greater than 10%, cephalexin is least likely to treat the infection effectively, despite the fact that the drug remains the most widely prescribed antibiotic for this indication, Dr. Hersh and his coauthors reported.

Choosing between trimethoprim/sulfamethoxazole and clindamycin remains a delicate decision, depending on CA-MRSA resistance and prevalence of group A strep in an individual community.

In San Francisco, the overall prevalence of S. aureus in cultures of purulent pediatric skin infections is 90% (80% of them caused by CA-MRSA; 20% caused by methicillin-sensitive S. aureus). Of the remaining 10%, cultures show group A strep more than 99% of the time, said Dr. Hersh during his late-breaking presentation.

Using these figures for a “base case” analysis, he concluded that probability rates for each drug having activity against an empiric skin infection were 95% for clindamycin, 89% for trimethoprim/sulfamethoxazole, and 28% for cephalexin.

Higher group A strep prevalence or high-rate clindamycin resistence in a community would tilt the decision tree model to trimethoprim/sulfamethoxazole or cephalexin, but it would be the rare community in which CA-MRSA prevalence was so low it would favor cephalexin for skin infections or other CA-MRSA affected conditions such as osteomyelitis or septic arthritis, said Dr. Hersh.

Dr. Myto Duong and associates in St. Louis selected trimethoprim/sulfamethoxazole for a randomized, controlled, double-blind trial comparing antibiotic treatment of skin and soft tissue infections with treatment with incision and drainage in 161 immunocompetent children.

All patients presented to the emergency department at Cardinal Glennon Children's Medical Center. About half of the children were less than 5 years old.

Wound cultures revealed CA-MRSA in 129 children (80%)–with 18% clindamycin resistant as well–and methicillin-sensitive Streptococcus aureus in 14 (9%). Other bacteria were responsible for the infections in the remaining cases, including group A strep in 1%.

Twelve patients were lost to follow-up.

Among patients with complete data available, complete resolution of the lesions was seen in 95% receiving a placebo following incision and drainage (with or without wound packing). Complete resolution was also seen in 96% of those who received incision, drainage, and a 10-day antibiotic prescription filled in the emergency department before children were discharged.

Compliance, defined as taking at least half of the medication prescribed, was poor, at just 66%.

Development of a new purulent skin lesion following treatment was equally likely in compliant patients receiving the antibiotic or placebo.

However, in the noncompliant subset, receipt of an antibiotic reduced the risk of developing a new purulent skin lesion. In this group, 23% of those receiving placebo developed a new lesion, compared with 4% who received an antibiotic prescription at the emergency department.

“Antibiotics may be useful in specific cases,” concluded Dr. Duong.

Both Dr. Hersh and Dr. Duong stated that they had no relevant financial conflicts to disclose.

HONOLULU – For community-acquired methicillin-resistant Staphylococcus aureus infections of the face, cephalexin should rarely be the antibiotic of choice, according to a decision analysis performed by researchers at the University of California, San Francisco, and presented at the annual meeting of the Pediatric Academic Societies.

A second study, this one from Cardinal Glennon Children's Medical Center in St. Louis, called into question whether an antibiotic is needed at all to treat a primary skin infection if abscesses are incised and drained.

In the San Francisco study, Dr. Adam Hersh and associates from the university weighed the tradeoffs associated with three antibiotic choices–cephalexin, trimethoprim/sulfamethoxazole, or clindamycin–for empiric treatment of a purulent skin infection in a child under the age of 18.

Cephalexin does not treat CA-MRSA; trimethoprim/sulfamethoxazole does not treat group A Streptococcus; while clindamycin treats both, CA-MRSA is becoming increasingly resistant to it in some communities, said Dr. Hersh.

When community physicians consistently culture skin infections and prevalence and resistance rates can be developed, a decision tree analysis can be a method of “exquisitely weighing the tradeoffs between treatment choices,” he commented.

In communities that now have a prevalence of CA-MRSA of greater than 10%, cephalexin is least likely to treat the infection effectively, despite the fact that the drug remains the most widely prescribed antibiotic for this indication, Dr. Hersh and his coauthors reported.

Choosing between trimethoprim/sulfamethoxazole and clindamycin remains a delicate decision, depending on CA-MRSA resistance and prevalence of group A strep in an individual community.

In San Francisco, the overall prevalence of S. aureus in cultures of purulent pediatric skin infections is 90% (80% of them caused by CA-MRSA; 20% caused by methicillin-sensitive S. aureus). Of the remaining 10%, cultures show group A strep more than 99% of the time, said Dr. Hersh during his late-breaking presentation.

Using these figures for a “base case” analysis, he concluded that probability rates for each drug having activity against an empiric skin infection were 95% for clindamycin, 89% for trimethoprim/sulfamethoxazole, and 28% for cephalexin.

Higher group A strep prevalence or high-rate clindamycin resistence in a community would tilt the decision tree model to trimethoprim/sulfamethoxazole or cephalexin, but it would be the rare community in which CA-MRSA prevalence was so low it would favor cephalexin for skin infections or other CA-MRSA affected conditions such as osteomyelitis or septic arthritis, said Dr. Hersh.

Dr. Myto Duong and associates in St. Louis selected trimethoprim/sulfamethoxazole for a randomized, controlled, double-blind trial comparing antibiotic treatment of skin and soft tissue infections with treatment with incision and drainage in 161 immunocompetent children.

All patients presented to the emergency department at Cardinal Glennon Children's Medical Center. About half of the children were less than 5 years old.

Wound cultures revealed CA-MRSA in 129 children (80%)–with 18% clindamycin resistant as well–and methicillin-sensitive Streptococcus aureus in 14 (9%). Other bacteria were responsible for the infections in the remaining cases, including group A strep in 1%.

Twelve patients were lost to follow-up.

Among patients with complete data available, complete resolution of the lesions was seen in 95% receiving a placebo following incision and drainage (with or without wound packing). Complete resolution was also seen in 96% of those who received incision, drainage, and a 10-day antibiotic prescription filled in the emergency department before children were discharged.

Compliance, defined as taking at least half of the medication prescribed, was poor, at just 66%.

Development of a new purulent skin lesion following treatment was equally likely in compliant patients receiving the antibiotic or placebo.

However, in the noncompliant subset, receipt of an antibiotic reduced the risk of developing a new purulent skin lesion. In this group, 23% of those receiving placebo developed a new lesion, compared with 4% who received an antibiotic prescription at the emergency department.

“Antibiotics may be useful in specific cases,” concluded Dr. Duong.

Both Dr. Hersh and Dr. Duong stated that they had no relevant financial conflicts to disclose.

HONOLULU – For community-acquired methicillin-resistant Staphylococcus aureus infections of the face, cephalexin should rarely be the antibiotic of choice, according to a decision analysis performed by researchers at the University of California, San Francisco, and presented at the annual meeting of the Pediatric Academic Societies.

A second study, this one from Cardinal Glennon Children's Medical Center in St. Louis, called into question whether an antibiotic is needed at all to treat a primary skin infection if abscesses are incised and drained.

In the San Francisco study, Dr. Adam Hersh and associates from the university weighed the tradeoffs associated with three antibiotic choices–cephalexin, trimethoprim/sulfamethoxazole, or clindamycin–for empiric treatment of a purulent skin infection in a child under the age of 18.

Cephalexin does not treat CA-MRSA; trimethoprim/sulfamethoxazole does not treat group A Streptococcus; while clindamycin treats both, CA-MRSA is becoming increasingly resistant to it in some communities, said Dr. Hersh.

When community physicians consistently culture skin infections and prevalence and resistance rates can be developed, a decision tree analysis can be a method of “exquisitely weighing the tradeoffs between treatment choices,” he commented.

In communities that now have a prevalence of CA-MRSA of greater than 10%, cephalexin is least likely to treat the infection effectively, despite the fact that the drug remains the most widely prescribed antibiotic for this indication, Dr. Hersh and his coauthors reported.

Choosing between trimethoprim/sulfamethoxazole and clindamycin remains a delicate decision, depending on CA-MRSA resistance and prevalence of group A strep in an individual community.

In San Francisco, the overall prevalence of S. aureus in cultures of purulent pediatric skin infections is 90% (80% of them caused by CA-MRSA; 20% caused by methicillin-sensitive S. aureus). Of the remaining 10%, cultures show group A strep more than 99% of the time, said Dr. Hersh during his late-breaking presentation.

Using these figures for a “base case” analysis, he concluded that probability rates for each drug having activity against an empiric skin infection were 95% for clindamycin, 89% for trimethoprim/sulfamethoxazole, and 28% for cephalexin.

Higher group A strep prevalence or high-rate clindamycin resistence in a community would tilt the decision tree model to trimethoprim/sulfamethoxazole or cephalexin, but it would be the rare community in which CA-MRSA prevalence was so low it would favor cephalexin for skin infections or other CA-MRSA affected conditions such as osteomyelitis or septic arthritis, said Dr. Hersh.

Dr. Myto Duong and associates in St. Louis selected trimethoprim/sulfamethoxazole for a randomized, controlled, double-blind trial comparing antibiotic treatment of skin and soft tissue infections with treatment with incision and drainage in 161 immunocompetent children.

All patients presented to the emergency department at Cardinal Glennon Children's Medical Center. About half of the children were less than 5 years old.

Wound cultures revealed CA-MRSA in 129 children (80%)–with 18% clindamycin resistant as well–and methicillin-sensitive Streptococcus aureus in 14 (9%). Other bacteria were responsible for the infections in the remaining cases, including group A strep in 1%.

Twelve patients were lost to follow-up.

Among patients with complete data available, complete resolution of the lesions was seen in 95% receiving a placebo following incision and drainage (with or without wound packing). Complete resolution was also seen in 96% of those who received incision, drainage, and a 10-day antibiotic prescription filled in the emergency department before children were discharged.

Compliance, defined as taking at least half of the medication prescribed, was poor, at just 66%.

Development of a new purulent skin lesion following treatment was equally likely in compliant patients receiving the antibiotic or placebo.

However, in the noncompliant subset, receipt of an antibiotic reduced the risk of developing a new purulent skin lesion. In this group, 23% of those receiving placebo developed a new lesion, compared with 4% who received an antibiotic prescription at the emergency department.

“Antibiotics may be useful in specific cases,” concluded Dr. Duong.

Both Dr. Hersh and Dr. Duong stated that they had no relevant financial conflicts to disclose.