Cefazolin sodium was tested in vitro against 308 isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Neisseria meningitidis, Haemophilus influenzae, Staphylococcus aureus, and enterococcus. Broth and
agar dilution and disk diffusion techniques were used with at least two sizes of inocula of organisms.
Cefazolin was also studied in the treatment of 85 hospitalized patients with a variety of serious
infections. In concentations of 5 mug or less/ml,
cefazolin inhibited and killed more than 90% of isolates of Enterobacteriaceae with the exception of
indole-positive Proteus and Enterobacter species. No isolate of P. aeruginosa and only a few of Enterobacter and enterococci were killed by 25 mug of
cefazolin/ml, a concentration readily attainable in serum with a 500-mg dose given intramuscularly.
Penicillin-susceptible as well as
penicillin-resistant isolates of S. aureus were killed by 1 mug or less of
cefazolin per ml; however, 25 mug/ml was required to kill 100% of the strains when the inoculum size was increased 100-fold.
Cefazolin treatment appeared effective in 82 of 85 patients, including four with
endocarditis.
Pain was minimal after
intramuscular injection, and
thrombophlebitis was not observed in those treated intravenously. No patient developed a positive Coombs test, and no evidence of renal toxicity was apparent in clinical studies.