Why is using antimicrobial drugs to kill large numbers of gram-negative bacteria in a short period of time a cause for medical concern?

Antibiotics that kill large numbers of gram-negative bacteria are primarily aminoglycosides and some higher generation cephalosporins. The major medical concern in antibiotic usage is antimicrobial resistance which can arise with improper use of antibiotics. On the other hand, higher generation antibiotics that are proven bactericidal can have more detrimental adverse effects for the patient.