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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 broad-spectrum coverage against many Gram-negative aerobic bacilli, including *Pseudomonas aeruginosa*.
## Primary Indications
* Serious Gram-negative infections (e.g., bacteremia, pneumonia, intra-abdominal infections).
* Synergistic coverage for Gram-positive endocarditis (e.g., *Staphylococcus*, *Streptococcus*, *Enterococcus*).
* Empiric treatment of neonatal sepsis.
* Urinary tract infections (when susceptible).
## Adult Dosing
* **Traditional Dosing:** 3–5 mg/kg/day divided every 8 hours.
* **Extended-Interval Dosing (EID):** 5–7 mg/kg every 24 hours (based on calculated creatinine clearance; adjust intervals per local nomogram, e.g., Hartford Nomogram).
* **Synergy Dosing (Endocarditis):** 1 mg/kg every 8 hours.
* **Note:** Always use Ideal Body Weight (IBW) if the patient is obese; use Adjusted Body Weight (AdjBW) if TBW > 120% of IBW.
## Pediatric Dosing
* **Neonates (0–28 days):** Dosing is highly weight and gestational age-dependent (e.g., 3.5–5 mg/kg every 12–24 hours).
* **Infants/Children:** 7.5 mg/kg/day divided every 8 hours or 5–7.5 mg/kg once daily (EID).
* **Caution:** Always consult local pediatric dosing protocols or references (e.g., Lexicomp/NeoFax) as they are highly specific to post-menstrual age.
## Dose Adjustments
* **Renal Impairment:** Mandatory. Dose reduction or interval extension is required based on CrCl calculations.
* **Obesity:** Use IBW or AdjBW to avoid toxicity.
* **Dialysis:** Requires post-hemodialysis supplemental dosing.
## Contraindications
* Hypersensitivity to aminoglycosides.
* Known history of severe vestibular or auditory toxicity.
* Myasthenia gravis (may exacerbate muscle weakness).
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; associated with trough accumulation.
* **Ototoxicity:** Vestibular (vertigo, ataxia) or auditory (tinnitus, hearing loss); often irreversible.
* **Neuromuscular Blockade:** Rare; typically associated with high doses or rapid infusion.
## Key Drug Interactions
* **Nephrotoxic agents:** Increased risk of renal failure with vancomycin, amphotericin B, cisplatin, cyclosporine, or NSAIDs.
* **Neuromuscular Blockers:** Potentiation of paralytic effects.
* **Loop Diuretics:** Increased risk of ototoxicity (e.g., furosemide, ethacrynic acid).
## Monitoring
* **Renal Function:** Serum creatinine and urine output daily.
* **Randomized Serum Concentrations:**
* *Traditional:* Measure peaks (30 mins after infusion) and troughs (30 mins before next dose).
* *EID:* Typically target a random level 6–14 hours post-infusion using specific nomograms.
* **Auditory/Vestibular:** Monitor for symptoms of dizziness, tinnitus, or hearing changes.
## Clinical Pearls
* **Synergy:** Gentamicin is rarely used as monotherapy for Gram-positives; it is used only to shorten the duration of therapy for endocarditis.
* **Drug-Disease Interaction:** Gentamicin is poorly absorbed orally; IV is the standard for systemic infections.
* **Local Governance:** Always defer to institutional antimicrobial stewardship guidelines for specific dose-finding nomograms and target ranges, as these vary significantly by hospital.
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*Disclaimer: This information is for educational purposes only and does not replace professional clinical judgment. Dosing and monitoring protocols vary by institution. Always verify specific patient details and current prescribing information against your local hospital formulary and the most recent package insert before clinical administration.*
