Prophylactic administration of penicillins for endocarditis does not reduce the incidence of postextraction bacteremia.

Sixty healthy patients were randomized to receive placebo, penicillin V (2 g), or amoxicillin (3 g) 1 hour before dental extraction was performed. Blood samples for microbiological investigation were collected before, during, and 10 minutes after surgery and were processed by lysis filtration under anaerobic conditions. There was no statistical difference among patients in the placebo group, the penicillin-V group, and the amoxicillin group in terms of incidence or magnitude of bacteremia due to viridans streptococci or anaerobic bacteria during extraction or 10 minutes after the procedure. The overall incidence rates of bacteremia after dental extraction were 95%, 90%, and 85%, respectively, for the three groups. For > 90% of 126 strains of viridans streptococci tested, the MICs of penicillin V and ampicillin were < or = 0.125 mg/L. The protective effect of prophylactically administered penicillins must be due to interference with crucial steps in the development of endocarditis (other than the transient bacteremia that occurs initially).