In Vitro Comparison of Gentamicin, Tobramycin, Sisomicin, and Netilmicin

Abstract

The antimicrobial activity of gentamicin, tobramycin, sisomicin, and netilmicin (Sch 20569) was compared against 150 strains of organisms. Netilmicin was shown to be the least effective against Pseudomonas strains but to have slightly better activity against Staphylococcus aureus and Escherichia coli than the other agents. The effect of calcium and magnesium in enhancing the differences in activity of these aminoglycosides against Pseudomonas strains was also demonstrated.This study was carried out to compare the in vitro antibacterial activity of four aminoglycoside antibiotics, gentamicin, tobramycin, sisomicin, and netilmicin (Sch 20569), against 148 clinical isolates and two control strains. There were 50 strains each of Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. The control organisms used were P. aeruginosa ATCC 27853 and E. coli ATCC 25922.Minimum inhibitory concentrations (MICs) were determined in the conventional manner in three types of broth: (i) brain heart infusion broth (BHI; BBL 11063) with added calcium and magnesium to provide levels of 75 and 20 mg/liter, respectively; (ii) BHI broth (BBL 11063) unmodified (calcium and magnesium levels were 36 and 14 mg/liter, respectively); and (iii) tryptone broth (Oxord L42). A medium control with no antibiotic added was provided for each organism tested to assure viability, and medium controls with no antibiotic and no organism were also used to assure sterility ofthe medium. Type (i) broth was used for Pseudomonas strains, type (ii) was used for E. coli strains, and type (iii) was used for S. aureus strains.Each tube, other than the medium controls, was inoculated with approximately 104 colonyforming units of the organism under test.The results of the MICs of the four antibiotics against these groups of organisms are shown in Fig. 1 (P. aeruginosa), Fig. 2 (S. aureus), and Fig. 3 (E. coli). These illustrate the relationship between MICs and cumulative percentages of strains inhibited.The most pronounced differences are shown with regard to P. aeruginosa (Fig. 1). At the concentration inhibiting 50% of the strains, the MIC of tobramycin was 0.48 ug/ml and that of netilmicin (Sch 20569) was 3.6 ,Lg/ml, whereas gentamicin and sisomicin were almost inseparable at 1.35 and 1.45 ,ug/ml, respectively. In effect, therefore, a sevenfold difference in activity between tobramycin and netilmicin was demonstrable against this group ofPseudomonas strains isolated using BHI broth with added calcium and magnesium. Figure 2, however, illustrates the converse, in that for the group of staphylococcal isolates tested, the 50% inhibition level was 0.01 ,ug of netilmicin (Sch 20569) and 0.03 ,ug of tobramicin per ml, indicating a threefold difference in activity, but in this instance with netilmicin showing the advantage. Gentamicin and sisomicin occupied intermediate positions in their activity.Netilmicin (Sch 20569) also showed an increase in activity compared with the other aminoglycosides tested against the group ofE. coli strains, although this dif...

Netilmicin: Its <i>in vitro </i>Activity and Synergism with Penicillin Compounds

“…20569), an ethyl deriva tive of sisomicin, was reported to be effec tive in vitro against aerobic gram-negative bacilli [1][2][3][4][5][6][7][8][9][10][11][12], It has been suggested that it may be less oto-and nephrotoxic than gen tamicin [6,7]. In clinical trials, this anti biotic was found to attain higher serum lev els than gentamicin [6,7], It is controversial if netilmicin is any more effective than gen tamicin against Pseudomonas aeruginosa and other gentamicin-resistant gram-nega tive bacilli [3,5,12].…”

Correlation of Netilmicin Agar Dilution and Disk Diffusion Susceptibilities

“…Netilmicin has been reported to have considerable activity against gram-negative clinical isolates (2,3,5,6,(8)(9)(10) and to be effective against some gentamicin-resistant strains (3,(7)(8)(9). This in vitro study evaluates the correlation between netilmicin agar dilution minimal inhibitory concentrations (MICs) and disk diffusion zone diameters.…”