Choice of AntibioticWhen antibiotic prophylaxis is indicated, practitioners should choose a prophylactic regimen based on several considerations, including the following:• The microbial flora present at the site of the procedure• The spectrum of activity, cost, and ease of administration of the antibiotic• Patient history of allergy or sensitivity to antibiotics Amoxicillin is the preferred antibiotic for endocarditis prophylaxis before most procedures because of its activity against viridans streptococci, favorable side effect profile, low cost, and reasonable bioavailability. When amoxicillin is contraindicated, other oral agents with activity against oral streptococci are reasonable alternatives before oral procedures, including clindamycin, first-generation cephalosporins, or macrolide antibiotics. However, for lower gastrointestinal or genitourinary procedures, vancomycin is recommended because of the perceived need to include coverage for enterococci. In addition, a single dose of an aminoglycoside antibiotic is recommended before lower gastrointestinal or genitourinary procedures in high-risk patients.
Risks of AntibioticsAnaphylaxis is a complication of antibiotic therapy and will occur approximately 4 to10 times per 100,000 patient-doses of prophylactic oral amoxicillin. For intravenous ampicillin courses, the rate of anaphylaxis may approach 15 to 20 per 100,000 patient-doses. Although anaphylaxis is the most commonly considered potential harm of antibiotic prophylaxis for IE, approximately 10 times more patients will experience minor allergic reactions to these antibiotics, predominantly rashes. In addition, use of even single-dose regimens of antibiotics could cause Clostridium difficile colitis, which has significant associated morbidity.The impact of short-course antibiotic prophylaxis for IE on the development of antimicrobial resistance is unknown. Population studies have not consistently shown a correlation between total antibiotic exposure and emergence of antimicrobial resistance. Although it is logical that increasing antibiotic use drives antimicrobial resistance, data to support this hypothesis have been inconsistent.
Practical ConsiderationsIdeally, antibiotics should be administered to ensure peak concentrator of the antibiotic at the initiation of the procedure. Prophylactic oral antibiotics should be taken 1 hour prior to the procedure. In patients who are unable to take oral medicine, or who are prescribed intravenous medications for prophylaxis, the intravenous antibiotic should be administered within 30 minutes of the procedure. Some animal data support a protective role for post-procedure antibiotics administered within 30 minutes of the procedure.Patients who are already taking (or have recently taken) antibiotics for other reasons should be prescribed a different antibiotic for prophylaxis of IE. For example, a patient who has completed a course of amoxicillin for a urinary tract infection within the past week might appropriately be given cephalexin prior to a tooth extraction. This is done with the presumption that the remaining bacterial flora in the patient’s mouth is likely to be those that are resistant to or tolerant of amoxicillin.*50/348/5*