What class of antibiotic is gentamicin?

Gentamicin is an Aminoglycoside Antibiotic

Gentamicin is classified as an aminoglycoside antibiotic, derived from the actinomycete Micromonospora purpurea. 1 This classification is clearly established in the FDA drug information and supported by multiple clinical guidelines.

Characteristics of Aminoglycosides

Aminoglycosides are characterized by:

• Mechanism of action: They work by binding to the 30S ribosomal subunit of bacteria, inhibiting protein synthesis
• Spectrum of activity: Broad-spectrum bactericidal activity, particularly effective against gram-negative organisms
• Pharmacokinetics:
  • Poor gastrointestinal absorption (requiring parenteral administration)
  • Concentration-dependent killing
  • Primarily excreted unchanged through the kidneys 2

Clinical Applications of Gentamicin

Gentamicin is indicated for the treatment of serious infections caused by susceptible strains of:

• Pseudomonas aeruginosa
• Proteus species (indole-positive and indole-negative)
• Escherichia coli
• Klebsiella-Enterobacter-Serratia species
• Citrobacter species
• Staphylococcus species 1

It is commonly used in:

1. Bacterial sepsis: Often combined with beta-lactams for empiric therapy in neonatal sepsis 3
2. Endocarditis: Used in combination with other antibiotics for synergistic effects, particularly for enterococcal endocarditis 3
3. Serious gram-negative infections: Especially for Pseudomonas infections 4
4. Urinary tract infections: When caused by susceptible organisms 5

Dosing Considerations

Dosing of gentamicin requires careful consideration due to its narrow therapeutic window:

• Standard adult dosing: Approximately 3 mg/kg/day in divided doses for most infections 3
• Pediatric dosing: Typically 5.6-7.5 mg/kg/day for infants 5
• Therapeutic monitoring: Essential to maintain peak concentrations of approximately 3 μg/mL and trough concentrations <1 μg/mL 3
• Dosing interval: Multiple daily divided doses are recommended for certain conditions like enterococcal endocarditis rather than once-daily dosing 3

Important Precautions

When using gentamicin, clinicians should be aware of:

1. Nephrotoxicity risk: Monitor renal function, especially with prolonged therapy
2. Ototoxicity risk: Can cause irreversible hearing loss or vestibular damage
3. Drug interactions: Incompatible with vancomycin, amsacrine, and fluconazole in admixtures 6
4. Monitoring requirements: Regular therapeutic drug monitoring is recommended, especially in patients with variable pharmacokinetics 7

Resistance Patterns

Resistance to aminoglycosides is increasing, particularly in:

• Enterococci with high-level aminoglycoside resistance 3
• Some strains of Pseudomonas and other gram-negative bacteria

In these cases, alternative antimicrobial strategies may be necessary.

Understanding gentamicin's classification as an aminoglycoside is essential for proper clinical application, dosing, monitoring, and anticipation of potential adverse effects.