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# IV Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic indicated for serious gram-negative bacterial infections. It exhibits concentration-dependent bactericidal activity and possesses a significant post-antibiotic effect. It is characterized by a narrow therapeutic index with potential for nephrotoxicity and ototoxicity.
## Primary Indications
* Serious infections caused by susceptible *Pseudomonas aeruginosa*, *Proteus* species, *E. coli*, *Klebsiella*, *Enterobacter*, and *Serratia*.
* Synergistic treatment for endocarditis (utilizing lower doses).
* Empiric treatment for sepsis (often in combination with a beta-lactam).
## Adult Dosing
* **Traditional (Multiple Daily Dose):** 3–5 mg/kg/day divided every 8 hours.
* **Extended Interval (Once-Daily):** 5–7 mg/kg every 24 hours (based on calculated creatinine clearance).
* **Endocarditis Synergy:** 1 mg/kg every 8 hours (total daily dose usually not exceeding 3 mg/kg).
* *Note: Dosing must be adjusted based on local institutional protocols and therapeutic drug monitoring (TDM).*
## Pediatric Dosing
* **Neonates (0–7 days):** 2.5–4 mg/kg every 12–24 hours (depending on gestational age and weight).
* **Infants/Children:** 2.5 mg/kg every 8 hours.
* *Note: Extended interval dosing is increasingly common in pediatrics; verify local weight-based protocols.*
## Dose Adjustments
* **Renal Impairment:** Mandatory dose reduction or interval extension is required based on CrCl. Use actual body weight for patients of normal weight; consider adjusted body weight for obesity.
* **Hepatic Impairment:** No standard adjustment required, but patients with ascites may require larger initial doses due to increased volume of distribution.
## Contraindications
* Hypersensitivity to aminoglycosides.
* Myasthenia gravis (may exacerbate muscle weakness).
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; manifests as rising serum creatinine.
* **Ototoxicity:** Often irreversible; presents as vestibular dysfunction (dizziness/vertigo) or auditory damage (tinnitus/hearing loss).
* **Neuromuscular Blockade:** Rare, but can lead to respiratory paralysis, especially if given with paralytics.
## Key Drug Interactions
* **Nephrotoxic/Ototoxic Agents:** Avoid or use with extreme caution alongside vancomycin, amphotericin B, cisplatin, cyclosporine, or loop diuretics.
* **Neuromuscular Blockers:** Potentiation of paralytic effects.
## Monitoring
* **Serum Concentrations:** Obtain trough levels (traditional) or random levels (extended-interval) to guide dosing and avoid toxicity.
* **Renal Function:** Monitor serum creatinine and BUN daily. Monitor urine output.
* **Auditory/Vestibular:** Monitor for symptoms of tinnitus or loss of balance.
## Clinical Pearls
* **TDM:** Timing of blood draws is critical for interpretation. Trough levels should be drawn 30 minutes prior to the next dose; peak levels 30 minutes after completion of a 30-minute infusion.
* **Obesity:** Use adjusted body weight for calculating dose to prevent toxic accumulation.
* **Incompatibility:** Do not mix in the same solution as penicillins or cephalosporins (inactivation occurs in the bag).
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**Educational Disclaimer:** This information is for educational purposes only. Clinical dosing protocols vary significantly by institution and patient-specific factors (e.g., hemodialysis, cystic fibrosis). Always consult your local hospital antibiogram, institutional dosing guidelines, and the most current manufacturer’s prescribing information before ordering or administering medication.
