Gentamicin
Garamycin
Aminoglycoside protein-synthesis inhibitor
Binds 30S ribosomal subunit, causes misreading of mRNA → defective bacterial protein synthesis. Bactericidal, concentration-dependent killing. Synergy with cell-wall agents (β-lactams, vancomycin) for gram-positive endocarditis.
Indications
- •Gram-negative infections (Pseudomonas, Klebsiella, E. coli)
- •Synergy in enterococcal or staphylococcal endocarditis
- •Surgical prophylaxis in penetrating bowel trauma (with anti-anaerobic agent)
- •Topical / ophthalmic / inhaled formulations for localized infection
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Once-daily extended-interval | 5–7 mg/kg IV q24 h; trough goal <1 mcg/mL | — |
| Traditional q8 h | 1–2 mg/kg IV q8 h; peak 6–10 mcg/mL, trough <2 mcg/mL | — |
| Endocarditis synergy | 1 mg/kg IV q8 h with β-lactam | — |
Pharmacokinetics
Onset minutes IV. Peak end-of-infusion. Half-life 2–3 h normal renal function (40+ h in ESRD). 99% renal excretion unchanged.
Hemodynamic effects
Minimal.
Respiratory effects
Potentiates non-depolarizing NMB at synaptic level — prolonged paralysis and post-op ventilation possible after large doses.
Side effects
- !Nephrotoxicity (dose- and duration-dependent; >5 days >10% incidence)
- !Ototoxicity — vestibular and cochlear; can be permanent. Cumulative-dose-dependent.
- !Neuromuscular blockade — synergizes with non-depolarizers; especially severe in myasthenia gravis
- !Pseudomembranous colitis (rare)
Contraindications
- ×Myasthenia gravis (relative — markedly potentiates weakness)
- ×Hypersensitivity
Clinical pearls
- ★OTOTOXICITY IS PERMANENT: counsel patients on chronic therapy (TB, endocarditis) about hearing screening; vestibular toxicity often irreversible.
- ★NMB INTERACTION: high-dose perioperative gentamicin + rocuronium can produce a profound block that outlasts sugammadex's typical reversal. Anticipate ICU monitoring or extended PACU.
- ★ONCE-DAILY DOSING: leverages concentration-dependent killing + post-antibiotic effect; equivalent efficacy with less nephrotoxicity for non-endocarditis indications.
- ★RENAL DOSING: requires real-time creatinine + level monitoring. Don't initiate at standard doses in CKD without pharmacy/ID input.
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Other drugs in Antibiotics
- Cefazolin
β-lactam — inhibits bacterial cell wall PBPs.
- Vancomycin
Inhibits cell wall synthesis (binds D-Ala-D-Ala). Active against MRSA + gram-positives.
- Clindamycin
Binds 50S ribosomal subunit, blocks peptide-bond formation. Bacteriostatic against most organisms; bactericidal against susceptible streptococci. Excellent activity against anaerobes and gram-positive cocci including community-acquired MRSA.
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