In vitro susceptibility of gentamicin-resistant Enterobacteriaceae and Pseudomonas aeruginosa to netilmicin and selected aminoglycoside antibiotics.

Netilmicin (Sch 20569), a semisynthetic aminoglycoside related to gentamicin C(1a), was evaluated in vitro in agar dilution testing against 224 different clinical isolates of gentamicin-resistant Enterobacteriaceae and Pseudomonas aeruginosa in parallel with amikacin, gentamicin, sisomicin, and tobramycin. Netilmicin showed a very high degree of activity against gentamicin-resistant organisms, but amikacin was more active in vitro, particularly against Providencia stuartii and P. aeruginosa. Sisomicin and tobramycin were consistently less active than either netilmicin or amikacin. Netilmicin was bactericidal in broth testing against P. aeruginosa. Netilmicin showed a greater difference between results with agar and broth dilution testing than did amikacin.