Antibiotic prophylaxis against infective endocarditis: time to rethink.

A decade of research has led to more precise guidelines for a complex health problem t has long been considered that all patients with heart conditions that predispose to infective endocarditis should receive antibiotic prophylaxis when undergoing procedures that can lead to bacteraemia with organisms known to cause endocarditis. However, the evidence for such action is surprisingly poor. 1 It is based on isolated case reports of endocarditis following dental or other procedures, and on theoretical considerations, rather than the results of randomised controlled trials. The American Heart Association (AHA) has published guidelines for endocarditis prophylaxis since 1955. In Australia, all editions of the Antibiotic guidelines (now Therapeutic guidelines: antibiotic, version 13 2) have also included recommendations for antibiotic prophylaxis against endocarditis. Of necessity, these guidelines have been complex, as three major variables were considered — the lifetime risk of endocarditis due to the underlying heart condition, the likelihood and nature of bacteraemia following the procedure, and the risk of adverse effects from antibiotic therapy. 2 The lifetime risk associated with the cardiac condition was divided into three risk categories (high, medium and low), and the likelihood of bacteraemia from a procedure was similarly divided into risk categories. Thus, prophylaxis has been firmly recommended for patients with an underlying heart condition who are at high risk of endocarditis and are undergoing a procedure that has a high risk of leading to significant bacteraemia. Conversely, it has not been recommended for patients with conditions who are at low risk of endocarditis and are undergoing procedures with a low risk of leading to significant bacteraemia. Prophylaxis has been " possibly " and " probably " recommended for various intermediate-risk combinations. Over the past 10 years, thinking has changed for three main reasons. First, there is now strong evidence that bacteraemia with endocarditis-causing organisms frequently occurs following everyday activities, such as tooth brushing. 3-6 Second, it has been recognised that very few cases of endocarditis can reasonably be attributed to a preceding procedure and are more likely to have resulted from everyday activities. Third, it has been realised that we should be more concerned about patients who are likely to have a poor outcome if they develop endocarditis than those who are at high risk of developing endocarditis at all. 1 In the context of this change in thinking, organisations around the world (including the AHA) have published new guidelines for endocarditis prophylaxis …