How To Choose Antibiotics For Staph Aureus Infections

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Continuing Education Course #113 — October 2003

I am very pleased to introduce the latest article, “How To Choose Antibiotics For Staph Aureus Infections,” in our CE series. This series, brought to you by HMP Communications, consists of regular CE activities that qualify for one continuing education contact hour (.1 CEU). Readers will not be required to pay a processing fee for this course.

Staph aureus infections are a common finding in lower extremity infections. In this article, Mark Kosinski, DPM, guides you through the plethora of choices in choosing an appropriate antibiotic.

Dr. Kosinski also discusses the rise and impact of MRSA as well as considerations in treating those with certain medical conditions.

At the end of this article, you’ll find a 10-question exam. Please mark your responses on the postage-paid postcard and return it to HMP Communications. This course will be posted on Podiatry Today’s Web site (www.podiatrytoday.com) roughly one month after the publication date. I hope this CE series contributes to your clinical skills.

Sincerely,

Jeff A. Hall
Editor-In-Chief
Podiatry Today

INSTRUCTIONS: Physicians may receive one continuing education contact hour (.1 CEU) by reading the article on pg. 53 and successfully answering the questions on pg. 58. Use the postage-paid card provided to submit your answers or log on to www.podiatrytoday.com and respond electronically.
ACCREDITATION: HMP Communications, LLC is approved by the Council on Podiatric Medical Education as a sponsor of continuing education in podiatric medicine.
DESIGNATION: This activity is approved for 1 continuing education contact hour or .1 CEU.
DISCLOSURE POLICY: All faculty participating in Continuing Education programs sponsored by HMP Communications, LLC are expected to disclose to the audience any real or apparent conflicts of interest related to the content of their presentation.
DISCLOSURE STATEMENTS: Dr. Kosinski has disclosed that he is a consultant and a member of the Speaker’s Bureau for Medicis and Pfizer.
GRADING: Answers to the CE exam will be graded by HMP Communications, LLC. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam.
TARGET AUDIENCE: Podiatrists.
RELEASE DATE: October 2003.
EXPIRATION DATE: October 31, 2004.
LEARNING OBJECTIVES: At the conclusion of this activity, participants should be able to:
• understand the effects of MRSA;
• differentiate among categories of antibiotics;
• understand considerations in prescribing antibiotics for pregnant women;
• discuss when endocarditis prophylaxis is indicated;
• determine antibiotic dose adjustments for patients undergoing hemodialysis; and
• discuss indications for recent advances in antibiotic therapy.

Sponsored by HMP Communications, LLC.

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MRSA infections (as shown above) are becoming increasingly more prevalent. The author notes that rates of nosocomial MRSA approach 60 percent in many ICUs. (Photo courtesy of Lawrence Karlock, DPM)
S. aureus is one of the most common infecting organisms seen in podiatry, including in simple paronychias like this one.
S. aureus infections are also commonly found in limb-threatening diabetic foot infections.
58
Author(s): 
By Mark Kosinski, DPM

The common thread shared by virtually all antibiotics relevant to podiatry is their activity against S. aureus. After all, S. aureus is by far the predominant infecting organism in lower extremity skin and skin structure infections. The rationale behind choosing an appropriate anti-staphylococcal drug is a daunting task given the ever-changing resistance pattern of this formidable organism.
Today, virtually all strains of S. aureus found in lower extremity infections produce beta-lactamase. Beta-lactamase (also known as penicillinase) is an enzyme that cleaves the beta-lactam ring and inactivates the antibiotic. Therefore, empiric therapy for suspected Staph infections should always include a beta-lactamase stable antibiotic. For this reason, it is useful to categorize antibiotics as being either beta-lactamase stable or beta-lactamase susceptible.
Drugs such as amoxicillin and ampicillin are beta-lactamase susceptible and should not be relied upon to treat lower extremity Staph infections. Patients will often begin self-treatment with these agents as they may have a few capsules left over from an ear or dental infection. However, they have minimal usefulness in the foot.
To overcome bacterial resistance, some drugs combine a beta-lactam antibiotic and a beta-lactamase inhibitor, thus creating a stable, new compound (such as amoxicillin/clavulanate, ampicillin/sulbactam, piperacillin/tazobactam and ticarcillin/clavulanate) with good activity against Staph. A useful side benefit of these additions is the extension of the drug’s spectrum to include B. fragilis, which makes the antibiotics attractive choices when anaerobic bacteria is an issue.

Nafcillin, oxacillin, dicloxacillin and, of course, methicillin, also known as the semisynthetic or penicillinase resistant penicillins, are all beta-lactamase stable as are the cephalosporins and carbapenems. Historically, methicillin was one of the first drugs developed to combat the growing number of beta-lactamase producing S. aureus infections. However, methicillin is no longer used due to adverse reactions. The primary reason to be familiar with the drug is because organisms resistant to the entire class have become known as “methicillin resistant.”
Other antibiotics are beta-lactamase stable and active against Staph by virtue of the fact that they are not beta-lactam compounds and thus do not contain a beta-lactam ring (see “Other Agents” in “Differentiating Antibiotic Categories” below). Although they have varying degrees of activity against S. aureus, they are often used to help treat patients who have a history of a penicillin allergy.

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