BLACK BOX WARNING
- nephrotoxicity — monitor renal function; ototoxicity — monitoring does not reliably prevent; neuromuscular blockade — respiratory paralysis possible
gentamicin
Brand: Garamycin
⚠ BBW TDM Required Prototype Drug
Drug Class: antibiotic
Drug Family: antibiotic
Subclass: aminoglycoside
Organ Systems: infectious-disease
Mechanism of Action
Irreversibly binds the 30S ribosomal subunit, causing misreading of mRNA and production of aberrant proteins; requires active transport into bacteria requiring oxygen — ineffective against obligate anaerobes; bactericidal and concentration-dependent.
30S ribosomal subunit
Indications
- serious gram-negative infections (bacteremia, pneumonia, UTI)
- synergistic therapy for gram-positive endocarditis (with penicillin or ampicillin)
- gentamicin-susceptible Pseudomonas infections
- prophylaxis in high-risk cardiac procedures (with ampicillin)
Contraindications
- severe aminoglycoside hypersensitivity
Adverse Effects
Common
- nephrotoxicity (reversible, proximal tubular injury)
- accumulation with multiple doses without monitoring
Serious
- nephrotoxicity (AKI — especially with concurrent nephrotoxins or pre-existing CKD)
- ototoxicity — cochlear (hearing loss, tinnitus) and vestibular (vertigo, imbalance) — may be irreversible
- neuromuscular blockade (high doses, especially with neuromuscular blocking agents)
Pharmacokinetics (ADME)
| Absorption | IV or IM; not absorbed orally (used topically for ocular/skin infections) |
| Distribution | Protein binding <10%; Vd 0.2–0.35 L/kg (increased in sepsis/burns); does not cross BBB |
| Metabolism | Not metabolized |
| Excretion | Entirely renal; half-life dramatically prolonged in renal failure |
| Half-life | 2–3 hours (normal renal function) |
| Onset | End of infusion |
| Peak | 30–60 minutes post-infusion |
| Duration | q8h (traditional); q24h (extended interval; preferred) |
| Protein Binding | <10% |
| Vd | 0.2–0.35 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| vancomycin | additive nephrotoxicity and ototoxicity | major |
| loop diuretics (furosemide) | additive ototoxicity; loop diuretics alone are ototoxic | major |
| neuromuscular blocking agents | aminoglycosides potentiate neuromuscular blockade | major |
Nursing Considerations
- Extended-interval dosing (extended interval gentamicin: 5–7 mg/kg q24h) is now the preferred approach in most institutions; it exploits concentration-dependent killing and post-antibiotic effect while reducing nephrotoxicity
- Therapeutic drug monitoring: for traditional q8h dosing, target peak 5–10 mcg/mL and trough <2 mcg/mL; for extended interval, use Hartford nomogram to assess trough at 6–14h post-infusion
- Monitor SCr and BUN every 24–48 hours; assess audiometric function if prolonged therapy (>5 days) or in patients with risk factors; question patients about tinnitus and balance
- Do not mix with penicillins in the same IV line — aminoglycosides are inactivated by penicillins in vitro; administer separately
Clinical Pearls
- Extended-interval aminoglycoside dosing (once-daily dosing) is as effective and less nephrotoxic than traditional dosing for most indications, exploiting concentration-dependent killing and the post-antibiotic effect
- Ototoxicity from aminoglycosides preferentially affects cochlear outer hair cells and vestibular hair cells — hearing loss may be irreversible and can continue progressing after drug discontinuation due to ongoing cellular damage
Safety Profile
Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.