Gentamicin antibacterial spectrum

This aminoglycoside (Figure 45-2) has an antibacterial spectrum similar to that of gentamicin. Although there is some cross-resistance between gentamicin and tobramycin, it is unpredictable in individual strains. Separate laboratory susceptibility tests are therefore necessary. 

Until now sisomicin and verdamicin have been relatively little modified. The 1-N-acyl derivatives could be obtained under controlled pH conditions. They show activity comparable to that of the parent compound l-ethyl-sisomidn (netilmicin) 241 was obtained through reaction with an excess of acetaldehyde and sodium borohydride Netilmicin shows an improved antibacterial spectrum. The hydrogenation of sisomicin gave 5 -epi-gentamicin Cia 236 (dihydrosisomicin) This simple conversion caused a substantial loss of activity. 

A 43-year-old male in the surgical ICU after exploratory laparotomy following a motor vehicle accident develops fever that is unresponsive to broad-spectrum antibacterial therapy (piperacillin-tazobactam 3.75 g every 6 hours, gentamicin 120 mg every 8 hours, and vancomycin 1 g every 12 hours). The patient has a central venous catheter and a Foley catheter. Blood cultures are negative at the time, but the patient has yeast growing in the sputum and urine. Laboratory studies reveal a white blood cell count of 11,300 cells/mm3 (11.3 x 109/L). 

Blepharitis is a topical inflammation of the eyelid margins that should be treated using topical antibacterial agents. Gentamicin eye ointment is preferred to the fusidic acid drops since the ointment is a better formulation to be used where the condition involves the eyelid margins. Chloramphenicol eye drops is the third option since it is an antibiotic with a wider spectrum of activity. A combination of corticosteroid and antibiotic is not recommended because of the side-effects associated with the steroid. The use of oral tablets is not usually recommended since blepharitis can easily be managed with topical drops. The use of dexamethasone eye drops, monotherapy steroid, could clear the inflammation but mask persistence of infection. 

Shows broad spectrum antibacterial activity against gentamicin resistant strains. Powder. Sol. H2O, MeOH fairly sol. EtOH, Me2CO poorly sol. EtOH, hexane. Mp 102-112°. [a]o +172 (c, 0.3 in H2O). Major component of complex. 

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