In vitro activity of Sch 21420, derivative of gentamicin B, compared to that of amikacin.

The minimal inhibitory concentration of Sch-21420 closely paralleled amikacin for 125 strains of aerobic gram-negative bacilli and Staphylococcus aureus primarily selected for testing because of resistance to other aminoglycoside antibiotics. Fifteen of 26 strains requiring 20 mug or more of amikacin per ml for inhibition were inhibited by two- to fourfold less Sch 21420. The majority of organisms resistant to both agents owed their resistance to mechanisms other than the carriage of aminoglycoside-modifying enzymes. Most strains carrying aminoglycoside 6'-acetyltransferase, capable of modifying amikacin, were susceptible to 10 mug or less of Sch 21420 per ml.