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# IV Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic that exerts bactericidal activity by binding to the 30S ribosomal subunit, inhibiting protein synthesis. It provides excellent coverage against aerobic gram-negative bacilli, including *Pseudomonas aeruginosa*.
## Primary Indications
* Complicated intra-abdominal infections (in combination).
* Complicated urinary tract infections.
* Skin and skin structure infections.
* Bacteremia/sepsis.
* Empiric treatment for suspected gram-negative infections.
* Synergistic treatment for endocarditis (gram-positive).
## Adult Dosing
* **Traditional Dosing:** 1–2.5 mg/kg every 8–12 hours.
* **Extended Interval Dosing (EID):** 5–7 mg/kg every 24–48 hours (based on renal function).
* **Endocarditis Synergy:** 1 mg/kg every 8 hours.
* *Note: Dosing is highly dependent on institutional protocols and actual body weight (or adjusted body weight in obesity).*
## Pediatric Dosing
* **Neonatal (0–28 days):** 2.5–5 mg/kg/dose based on post-menstrual age and weight; interval varies from every 18 to 48 hours.
* **Infants/Children:** 2.5 mg/kg/dose every 8 hours (traditional) or 5–7.5 mg/kg/dose once daily (EID, institutional dependent).
## Dose Adjustments
* **Renal Impairment:** Required. Consult local guidelines for CrCl-based nomograms.
* **Obesity:** Use Adjusted Body Weight (AdjBW) if calculated weight is significantly higher than ideal body weight to prevent toxicity.
* **Dialysis:** Supplemental dosing required post-hemodialysis.
## Contraindications
* Hypersensitivity to gentamicin or other aminoglycosides.
* Myasthenia gravis (relative).
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; associated with prolonged high troughs.
* **Ototoxicity:** Irreversible; vestibular (vertigo/ataxia) or cochlear (hearing loss/tinnitus).
* **Neuromuscular Blockade:** Rare, but can occur with rapid infusion or high systemic levels.
## Key Drug Interactions
* **Nephrotoxic Agents:** Increased risk with vancomycin, amphotericin B, NSAIDs, and loop diuretics.
* **Neuromuscular Blocking Agents:** May enhance paralysis.
* **Loop Diuretics:** Increased risk of ototoxicity.
## Monitoring
* **Serum Concentrations:** Obtain levels per institutional protocol. For traditional dosing, measure trough (30 min pre-dose) and peak (30 min post-infusion). For EID, use random levels (e.g., 6–14 hours post-dose) plotted on a Hartford nomogram.
* **Renal Function:** Monitor serum creatinine and BUN daily.
* **Clinical:** Monitor for signs of ototoxicity (vertigo, hearing changes) and intake/output.
## Clinical Pearls
* **Concentration-Dependent Killing:** Gentamicin exhibits a post-antibiotic effect (PAE), making high peak concentrations (relative to MIC) the primary driver of efficacy.
* **Volume of Distribution:** Aminoglycosides are hydrophilic; they distribute into extracellular fluid, not adipose tissue.
* **Incompatibility:** Do not mix with beta-lactams in the same IV line/bag (will inactivate the aminoglycoside).
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**Educational Disclaimer:** This information is for educational purposes only. Gentamicin dosing must be individualized based on institutional protocols, patient-specific pharmacokinetics, and clinical judgment. Always verify current prescribing information and local susceptibility patterns before administration.
