Sch 29482, a new penem antibiotic: evaluation of in-vitro activity and effect of test conditions

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Abstract
A new penem antibiotic, Sch 29482 (SCH), was shown to be active against a large number of Gram-negative and Gram-positive isolates. SCH was, in general, eightfold less potent than cefotaxime against sensitive Gram-negative organisms, but eightfold more potent against staphylococci. For SCH, the ratio of MICs against cephalothinsensitive strains to those against cephalothin-resistant strains was lower than any other tested compound, indicating SCH had good activity against many β -lactamase containing strains. Only against cefoperazone-resistant Serratia and ampicillin resistant Staphylococcus did SCH show a loss of activity. A very small inoculum size effect was observed with both β -lactam-sensitive and -resistant strains. Among 216 strains tested, only a few had higher MICs with SCH in broth media than on agar media. These results suggest that SCH has unusual stability to most β -lactamases. The activity of SCH was not significantly affected by different broth constituents nor by pH changes in the range of 6.5−7.9. Increases in MICs caused by the addition of 4% BSA to the test medium indicate that serum protein binding may be greater than 90%. The bactericidal activity of SCH against both Gram-negative and Gram-positive strains was superior to that observed with cefoxitin and cefotaxime.

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