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# Gentamicin (IV)
## Overview
Gentamicin is an aminoglycoside antibiotic that acts by binding to the 30S ribosomal subunit, inhibiting bacterial protein synthesis. It provides concentration-dependent bactericidal activity against many aerobic gram-negative bacilli (including *Pseudomonas aeruginosa*).
## Primary Indications
* Serious Gram-negative infections (e.g., sepsis, pneumonia, complicated UTI).
* Synergistic treatment of Gram-positive endocarditis (e.g., *Enterococcus* or *Staphylococcus* species) in combination with a cell-wall active agent.
## Adult Dosing
* **Empiric/Extended Interval (Once-Daily):** 5–7 mg/kg/dose every 24 hours (based on actual body weight; use adjusted body weight in obesity).
* **Traditional/Multiple Daily Dosing:** 1–2.5 mg/kg every 8 hours.
* **Synergy (Endocarditis):** 1 mg/kg every 8–12 hours.
* **Maximum:** Dosing is highly patient-specific; target serum concentrations determine safety.
## Pediatric Dosing
* **Neonates (Post-menstrual age dependent):** 3–5 mg/kg every 24–48 hours (refer to local neonatology nomograms for specific post-natal age/weight adjustments).
* **Infants/Children:** 2.5 mg/kg every 8 hours (traditional) OR 5–7.5 mg/kg every 24 hours (extended interval).
## Dose Adjustments
* **Renal Impairment:** Requires interval extension or dose reduction based on CrCl. Use the Hartford Nomogram or similar facility-specific protocols for once-daily dosing.
* **Obesity:** Use Adjusted Body Weight (AdjBW) for calculating the loading and maintenance dose to reduce toxicity risk.
## Contraindications
* Hypersensitivity to aminoglycosides.
* Use with caution in patients with neuromuscular disorders (e.g., myasthenia gravis) as it may exacerbate muscle weakness.
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; associated with prolonged high trough levels.
* **Ototoxicity:** Often irreversible; presents as vestibular dysfunction (dizziness/vertigo) or auditory damage (tinnitus/hearing loss).
* **Neuromuscular Blockade:** Rare but severe, especially with rapid infusion or significant electrolyte abnormalities (hypocalcemia/hypomagnesemia).
## Key Drug Interactions
* **Loop Diuretics (e.g., Furosemide):** Increased risk of ototoxicity.
* **Nephrotoxic Agents (e.g., Vancomycin, Amphotericin B, NSAIDs, Cisplatin):** Increased risk of acute kidney injury.
* **Neuromuscular Blocking Agents:** Potential for potentiated respiratory paralysis.
## Monitoring
* **Serum Concentrations:**
* *Extended interval:* Random level (typically 6–14 hours post-dose) plotted on a nomogram.
* *Traditional:* Trough levels (drawn within 30 minutes prior to the 3rd or 4th dose) and peak levels (drawn 30 minutes after completion of a 30-minute infusion).
* **Renal Function:** Monitor Serum Creatinine and BUN at least daily.
* **Clinical:** Monitor for signs of hearing loss, vertigo, or reduced urine output.
## Clinical Pearls
* **Extended Interval Dosing:** Generally preferred to minimize toxicity and optimize the peak-to-MIC ratio; **do not** use for patients with CrCl < 20-30 mL/min, those who are pregnant, or for synergy in endocarditis.
* **Site of Infection:** Poor tissue penetration into the CNS; intrathecal/intraventricular administration may be required for meningitis.
* **Compatibility:** Do not physically mix with beta-lactam antibiotics in the same IV line, as they can chemically inactivate one another over time.
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**Disclaimer:** This information is for educational purposes only. Clinical protocols may vary significantly by institution. Always verify specific dosing, safety, and compatibility information using current facility-approved guidelines, the drug package insert, or professional reference tools like Lexicomp or Micromedex before prescribing or administering medication.
