Cefazolin is a new antibiotic derived from 7-aminocephalosporanic acid, having the structure of 7-[l-(lH)-tetrazolylacetamido]-3-[2-(5-methyl-l, 3, 4-thiadiazolyl)-thiomethyl]-Δ
3-cephem-4-carboxylic cid. This substance is a broad-spectrum antibiotic, active
in vitro against most of Gram-positive and Gram-negative species of bacteria except for
Ps. aeruginosa, and is also active against penicillinase-producing strains of
Staph. aureus. The activity of cefazolin against fresh isolates of
E. coli and
Kl. pneumoniae seems superior to those of other antibiotics used in this study. The
in vitro activity of cefazolin is little influenced by size of inoculum, presence of rabbit serum, or kinds or properties of test medium. The activity of cefazolin is apparently bactericidal against both Gram-positive and Gram-negative bacteria at or above the MIC levels. In experiments on the development of resistance
in vitro, the MICs of cefazolin against
Staph. aureus strain 209P and
E. coli strain NIHJ increase slowly in a stepwise over a period of 17 transfers. The rate of resistance development of cefazolin is comparable with that of cepholoridine or ampicillin. Cefazolin is relatively stable to enzymes from
Staph. aureus and
E. coli, which readily inactivate ampicillin and benzyl penicillin. Cefazolin is not remarkably degraded by the tissue homogenates of rat, although cephalothin is degraded quite rapidly. Cefazolin, in the single subcutaneous dose, shows excellent protecting activity against experimental infections in mice infected with both PC-sensitive and resistant strains of
Staph. aureus, and is also fairly effective against infections in mice with
Diplococcus pneumoniae,
E. coli and
Proteus mirabilis.
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