Bacteremia after oral surgery and antibiotic prophylaxis for endocarditis.

The use of antibiotic prophylaxis in patients predisposed to infective endocarditis (IE) who are undergoing oral surgery procedures is widely accepted. Because there have been no controlled clinical trials of antibiotic regimens for the prevention of endocarditis in humans, recommendations are based on the results of prophylaxis studies in animal models of endocarditis, in vitro susceptibility data of pathogens that cause endocarditis, procedure-related studies of bacteremia, and studies of the efficacy of antimicrobial prophylaxis for prevention of postsurgical bacteremia. Minimizing the occurrence of postoperative bacteremia has been considered the most important factor in the prevention of IE, and the results of several clinical studies using conventional blood culture systems have demonstrated a marked reduction in bacteremia following dental extraction with the use of antibiotic prophylaxis. In recent studies using lysing and filtration of blood, prophylactic administration of penicillin V, amoxicillin, erythromycin, clindamycin, or cefaclor did not reduce the incidence or the magnitude of bacteremia after dental extraction, as compared to placebo. The antimicrobial mechanism of protection for IE is apparently different from a mere killing in blood. The implications of this for prophylaxis for IE in humans is still not fully understood, but studies of animals suggest that the protective effect may be exerted by inhibiting bacterial growth on the vegetations, thus allowing host defense mechanisms to gradually eliminate the bacteria from the valves. Microorganisms circulating in blood may settle on heart valves that are damaged or rendered defective by acquired or congenital disease and thereby cause IE. The disease remains prevalent, with approximately the same incidence as 40 years ago, and is associated with a mortality rate between 15% and 30%, despite advances in antimicrobial therapy and cardiovascular surgery. Dental treatment has often been regarded as a major cause of the disease, mainly because of the high frequency of bacteremia after various oral invasive procedures and because of the high recovery rate of viridans streptococci in IE cases [1, 2]. The concept of antibiotic prophylaxis for IE in patients with underlying heart disease has been widely accepted, and guidelines and specific antibiotic regimens have been recommended by various national boards [3, 4]. For ethical as well as practical reasons, there has been no clinical documentation of the efficacy of antibiotics in preventing IE in humans, and therefore the guidelines are based mainly on data from experimental animal models, pharmacokinetic studies, bacterial susceptibility studies, clinical experience, and studies of procedure-related bacteremia and the efficacy of antimicrobial prophylaxis for bacteremia. In animal studies, prophylactic administration of antibiotics has been attributed to effects such as rapid bacterial killing in blood, decreased bacterial adhesion to heart valves, and inhibition of bacterial growth on the heart valves, whereas studies in humans have mainly focused on the preventive effect on postsurgical bacteremia. Results of clinical studies have indicated an immediate and marked reduction in bacteremia following dental extraction when prophylactic antibiotics were used, whereas other studies have questioned the efficacy of antibiotic prophylaxis for postextraction bacteremia. Herein, we review the data published concerning bacteremia after oral surgical procedures and antibiotic prophylaxis.