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# IV Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic that acts via inhibition of bacterial protein synthesis by binding to the 30S ribosomal subunit. It exhibits concentration-dependent bactericidal activity and a significant post-antibiotic effect.
## Primary Indications
Used primarily for serious infections caused by susceptible Gram-negative bacilli (e.g., *Pseudomonas aeruginosa*, *Enterobacteriaceae*), often in combination with a beta-lactam for synergistic coverage (e.g., endocarditis).
## Adult Dosing
* **Conventional Dosing:** 1–2.5 mg/kg per dose administered every 8–12 hours.
* **Extended-Interval ("Once-Daily") Dosing:** 5–7 mg/kg administered every 24 hours.
* *Note: Dosing must be adjusted based on renal function and local institutional protocols.*
## Pediatric Dosing
* **Neonates (0–28 days):** 2.5–5 mg/kg/dose based on gestational age and post-natal age, usually every 12–24 hours.
* **Infants/Children:** 2.5 mg/kg/dose every 8 hours (conventional) or 5–7.5 mg/kg/dose every 24 hours (extended-interval).
## Dose Adjustments
* **Renal Impairment:** Dosing frequency must be extended (e.g., q24h, q48h) or doses reduced based on creatinine clearance (CrCl). Consult institutional nomograms.
* **Obesity:** Use adjusted body weight for patients with significant obesity to avoid toxicity.
## Contraindications
Hypersensitivity to gentamicin or other aminoglycosides. Use caution in patients with myasthenia gravis, parkinsonism, or pre-existing renal/vestibular impairment.
## Adverse Effects
* **Nephrotoxicity:** Typically reversible; monitor serum creatinine and urine output.
* **Ototoxicity:** Often irreversible; presents as vestibular (dizziness, vertigo) or auditory (tinnitus, hearing loss) dysfunction.
* **Neuromuscular Blockade:** Rare but severe, especially with rapid infusion or neuromuscular blocking agents.
## Key Drug Interactions
* **Nephrotoxic/Ototoxic Agents:** Avoid or use with extreme caution alongside vancomycin, amphotericin B, cisplatin, or loop diuretics (e.g., furosemide).
* **Neuromuscular Blockers:** Potential for prolonged paralysis/respiratory depression.
## Monitoring
* **Renal Function:** Daily serum creatinine and BUN.
* **Serum Drug Concentrations:**
* *Conventional:* Obtain trough levels (usually < 2 mcg/mL) 30 minutes before the 3rd or 4th dose.
* *Extended-Interval:* Use a random level 6–14 hours post-infusion plotted on a Hartford nomogram.
* **Toxicity:** Monitor for signs of hearing loss, imbalance, or decreased urine output.
## Clinical Pearls
* **Synergy:** Gentamicin is frequently used at low doses (e.g., 1 mg/kg) in combination with penicillins or vancomycin for endocarditis treatment; these regimens require specific monitoring of both peak and trough levels.
* **Infusion:** Administer over 30–60 minutes to minimize risks of infusion-related reactions.
* **Dosing Complexity:** Weight-based dosing is critical, but levels must always guide adjustments. Always verify current institutional guidelines as they supersede general dosing recommendations.
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**Disclaimer:** This information is for educational purposes only. Always consult current institutional protocols, official package inserts, and clinical pharmacists before prescribing or administering medication.
