Chemotherapy of experimental streptococcal endocarditis. V. Effect of duration of infection and retained intracardiac catheter on response to treatment.

The dynamics of infection and response to penicillin G (P) or combined P plus streptomycin (S) therapy were studied in a rabbit model of penicillin-sensitive Streptococcus sanguis endocarditis. Increased delay between infection and initiation of treatment required longer duration of therapy to effect a cure. Irrespective of the interval between infection and onset of therapy, P combined with S regularly eliminated streptococci from endocardial vegetations more rapidly than P alone, both in the presence and absence of an intracardiac catheter--although the difference in response was more marked with the catheter present. The combination of P and S consistently showed superior in vivo bactericidal activity compared to P alone in established S. sanguis endocarditis.