Abstract
Laboratory studies on a new synthetic penicillin, dimethoxy-phenyl-penicillin-Na (Staphcillin), were undertaken and the following results were obtained.
1. Minimum inhibitory concentration of Staphcillin against a variety of organisms was essentially similar to that of penicillin G or Syncillin.
2. The sensitivity of strains of Staphylococcus aureus isolated from clinical materials to penicillin G varied greatly (<0.2 mcg/ml->100 mcg/ml), but was uniformly sensitive to Staphcillin (1.6-3.1 mcg/ml).
3. Minimum inhibitory concentration of penicillin G sensitive or resistant strains of Staphylococcus aureus against penicillin G or Staphcillin was increased in accordance with the inoculum size. This phenomenon was evidently observed in penicillin G resistant strains against penicillin G, and in penicillin G sensitive strains against Staphcillin.
4. No effect of the presence of 50% bovine serum on the minimum inhibitory concentration using sensitive and resistant strains of Staphylococcus aureus was observed.
5. Whereas penicillin G was markedly destroyed by Staphylococcus aureus penicillinase, Staphcillin was extremely resistant,
6. Staphylococcus aureus promptly acquired resistance against penicillin G, but slowly and weakly against Staphcillin.
7. Maximum concentration of Staphcillin in serum following intramuscular injection occurred at 30 or 60 minutes and was rapidly disappeared in a few hours.
