INTRODUCTION

Antimicrobial prophylaxis for bacterial endocarditis has become standard in most developed countries, despite the fact that no prospective randomized trial has proven that such therapy is beneficial. Furthermore, given the extremely low incidence of endocarditis following procedures such as dental surgery and the medicolegal climate in the United States and Europe, it is unlikely that such a study will ever be undertaken. It has been estimated that a randomized trial to assess the effectiveness of prophylaxis after dental procedures would require at least 6000 patients in each study group [1].

The theoretical basis for antimicrobial prophylaxis for endocarditis and the most recent guideline that was published by the American Heart Association (AHA) in 2007 on the prevention of infective endocarditis will be reviewed here [2]. As will be seen, this guideline made important revisions to previous guidelines. (See 'AHA guideline' below.)

THEORETICAL BASIS FOR PROPHYLAXIS

The pathogenesis of infective endocarditis (IE) is presumed to involve the following sequence of events [3]:

• Formation of a small noninfected thrombus on an abnormal endothelial surface
• Secondary infection of this nidus with bacteria that are transiently circulating in the bloodstream
• Proliferation of bacteria resulting in the formation of vegetations on the endothelial surface

Since the occurrence of bacteremia is crucial to the initiation of an episode of IE, it is theoretically reasonable to conclude that preventing or promptly treating transient bacteremia will prevent the above sequence even if a predisposing valvular lesion is present.