Co-trimoxazole versus nafcillin in the therapy of experimental meningitis due to Staphylococcus aureus.

Co-trimoxazole was compared with nafcillin against Staphylococcus aureus in vitro and in the therapy of experimental Staph. aureus meningitis in rabbits. Co-trimoxazole (trimethoprim:sulphamethoxazole in a 1:20 ratio) was synergistic against 22/24 strains of Staph. aureus in vitro. The MBC90 of co-trimoxazole and nafcillin were 0.156-3.12 mg/l and 0.25 mg/l, respectively, concentrations below those achievable in purulent cerebrospinal fluid. The rate of bacterial killing (Staph. aureus) by co-trimoxazole and nafcillin were similar in both broth and pooled CSF in vitro. However, the MBC increased and the rate of bactericidal activity of both agents declined when tested in CSF at a higher inoculum (10(7) cfu/ml). During continuous intravenous infusion therapy of a reproducible, uniformly fatal (if untreated) model of experimental Staph. aureus meningitis, serum concentrations of all agents closely approximated those found in humans receiving standard parenteral regimens. The mean percent penetration into CSF ([CSF]/[serum] X 100) was 2.9, 35.6 and 27.1% for nafcillin, trimethoprim and sulphamethoxazole, respectively. Although both nafcillin and co-trimoxazole therapy reduced CSF Staph. aureus concentrations significantly more rapidly (P less than 0.001) when compared to untreated controls, the bactericidal rate was modest. The CSF was rendered sterile in 0/64 animals treated with either regimen for 8 h. Nafcillin was more rapidly bactericidal in vivo (P less than 0.03) than co-trimoxazole in this model. Caution is advised in the use of co-trimoxazole for infections of the central nervous system caused by Staph. aureus.

Imipenem therapy of experimental Staphylococcus aureus and Streptococcus faecalis endocarditis.

Imipenem was very active in vitro against 36 Staphylococcus aureus isolates from cases of infective endocarditis; the MBC90 was 0.06 mg/l (four- to eight-fold more active than nafcillin). The in-vitro activity of imipenem against 22 Streptococcus faecalis isolates from proven endocarditis cases was similar to that of penicillin G (MBC90 = 8 mg/l). Imipenem was compared with nafcillin and with penicillin plus gentamicin in the therapy of experimental endocarditis induced in rabbits by Staph. aureus and Str. faecalis, respectively. The dosages were chosen to simulate closely serum antibiotic concentrations found in humans receiving standard parenteral regimens. Imipenem was more rapidly bactericidal than nafcillin in experimental staphylococcal endocarditis. The mean +/- S.D. Staph. aureus concentrations within aortic valve vegetations (log10 cfu/g) after 5 days of therapy were as follows: imipenem = 1.39 +/- 0.61 versus nafcillin 2.39 +/- 0.36 (P less than 0.02). Both the imipenem and nafcillin regimens resulted in 'sterile' vegetations in congruent to 50% of rabbits with experimental staphylococcal endocarditis after 5 days of therapy (P greater than 0.05). Imipenem was also equivalent to penicillin plus gentamicin in the therapy of experimental enterococcal endocarditis for 5 days, as assessed by the mean cfu/g vegetation and the percentage of vegetations rendered sterile. However, 7 days of therapy cured experimental enterococcal endocarditis in 72% of rabbits receiving penicillin plus gentamicin versus 20% for imipenem alone (P less than 0.05). Imipenem deserves further evaluation in the therapy of infective endocarditis, both in experimental animal models of infection and in humans. This agent may prove useful in the therapy of staphylococcal endocarditis in a variety of difficult clinical situations. Therapy of enterococcal endocarditis with imipenem alone is not advisable, pending further data.