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# IV Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic that acts via irreversible binding to the 30S ribosomal subunit, inhibiting bacterial protein synthesis. It provides concentration-dependent bactericidal activity, primarily against Gram-negative aerobes.
## Primary Indications
* Complicated urinary tract infections
* Septicemia/Bacteremia
* Intra-abdominal infections (usually in combination with anti-anaerobics)
* Endocarditis (synergistic dosing)
* Nosocomial pneumonia (in combination with other agents)
## Adult Dosing
* **Conventional Dosing:** 1.5–2.5 mg/kg IV every 8 hours.
* **Extended Interval Dosing (EID):** 5–7 mg/kg IV every 24 hours (or frequency based on nomograms like Hartford).
* **Synergy for Endocarditis:** 1 mg/kg IV every 8 hours.
* **Max Dose:** Generally capped at 7 mg/kg per dose unless serum levels dictate otherwise; avoid exceeding 480 mg per dose without pharmacy consultation due to toxicity risks.
## Pediatric Dosing
* **Neonates (Postnatal Age $\le$ 7 days):** 4–5 mg/kg every 24–48 hours (adjust by weight/gestational age).
* **Infants/Children:** 2.5 mg/kg IV every 8 hours (conventional) or 7.5 mg/kg IV once daily (EID).
* *Note:* Pediatric dosing is highly protocol-dependent; consult institutional guidelines for specific nomograms.
## Dose Adjustments
* **Renal Impairment:** Requires dose frequency adjustment or amount reduction based on CrCl. Use Cockcroft-Gault for estimates. Serum concentration monitoring is mandatory.
* **Obesity:** Dosing should be based on Adjusted Body Weight (AdjBW) if actual body weight is >20% above ideal body weight.
## Contraindications
* Hypersensitivity to aminoglycosides.
* Myasthenia gravis (may exacerbate muscle weakness).
* Use caution in patients with pre-existing vestibulocochlear or renal impairment.
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; associated with prolonged trough levels.
* **Ototoxicity:** Often irreversible; involves auditory (hearing loss) or vestibular (vertigo/ataxia) dysfunction.
* **Neuromuscular blockade:** Rare; 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.
* **Ototoxic agents:** Increased risk with loop diuretics (e.g., furosemide).
* **Neuromuscular blockers:** May potentiate paralytic effects.
## Monitoring
* **Serum Concentrations:** Obtain levels for therapy >48 hours or in renal insufficiency.
* *Conventional:* Draw trough 30 minutes before 3rd or 4th dose.
* *EID:* Draw random level 6–14 hours after the first dose and plot against a nomogram.
* **Renal Function:** Monitor SCr, BUN, and urine output daily.
* **Auditory/Vestibular:** Monitor for hearing loss, tinnitus, or dizziness.
## Clinical Pearls
* **Infusion:** Administer over 30–60 minutes.
* **Synergy:** When used for endocarditis, gentamicin is combined with a cell-wall active agent (e.g., penicillin) to achieve synergy; monitor levels closely (trough < 1 mcg/mL usually targeted to prevent toxicity).
* **Incompatibility:** Do not mix in the same solution as penicillins or cephalosporins (inactivation occurs in vitro).
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice protocols vary by institution. Always verify specific dosages, infusion rates, and compatibility with local hospital guidelines and the most current manufacturer-approved prescribing information before administration.
