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# Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. It exhibits concentration-dependent bactericidal activity and a significant post-antibiotic effect.
## Primary Indications
* Serious Gram-negative infections (e.g., *Pseudomonas aeruginosa*, *Enterobacter*, *Klebsiella*)
* Synergistic treatment for Gram-positive endocarditis (e.g., *Enterococcus*, *Staphylococcus*)
* Empiric treatment for sepsis (often combined with a beta-lactam)
## Adult Dosing
* **Traditional (Divided Dosing):** 1–2 mg/kg IV every 8 hours.
* **Extended-Interval (Once-Daily) Dosing:** 5–7 mg/kg IV administered every 24 hours. *Note: Dosing is highly dependent on institutional nomograms (e.g., Hartford Nomogram).*
* **Synergy for Endocarditis:** 1 mg/kg IV every 8 hours (usual max 3–5 mg/kg/day total).
## Pediatric Dosing
* **Neonates (Post-menstrual age dependent):** Typically 3–5 mg/kg per dose; interval determined by gestational age (e.g., every 24–48 hours).
* **Infants/Children:** 2.5 mg/kg/dose IV every 8 hours; up to 7.5 mg/kg/day divided every 8 hours for severe infections.
* *Requirement:* Pediatric dosing is highly protocol-specific based on age and weight; verify against institutional neonatology/pediatric guidelines (e.g., Neofax).
## Dose Adjustments
* **Renal Impairment:** Required for all patients. Reduce frequency or dose based on measured or estimated creatinine clearance (CrCl).
* **Obesity:** Use adjusted body weight (ABW) or ideal body weight (IBW) if underweight/obese, per local protocol to calculate volume of distribution.
## Contraindications
* Hypersensitivity to aminoglycosides.
* Known severe renal impairment (relative; requires dose modification).
* Myasthenia gravis (may exacerbate muscle weakness).
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; associated with trough levels.
* **Ototoxicity:** Vestibular (dizziness, vertigo) or auditory (tinnitus, hearing loss); potentially irreversible.
* **Neuromuscular Blockade:** Rare, usually with high doses or rapid administration.
## Key Drug Interactions
* **Nephrotoxic agents:** Increased risk of renal failure (e.g., NSAIDs, vancomycin, amphotericin B, IV contrast, cyclosporine).
* **Ototoxic agents:** Increased risk of hearing loss (e.g., loop diuretics, cisplatin).
* **Neuromuscular blocking agents:** Potentiates effect (e.g., rocuronium, succinylcholine).
## Monitoring
* **Serum Concentrations:** Obtain troughs within 30 minutes prior to the 4th dose for traditional dosing. For extended-interval dosing, draw a "random level" (typically 6–14 hours post-infusion) and plot on an institutional nomogram.
* **Renal Function:** Serum creatinine and BUN; evaluate urine output.
* **Auditory/Vestibular:** Monitor for hearing changes or balance issues.
## Clinical Pearls
* **Dosing Weight:** For obese patients, seek guidance on whether to use actual, ideal, or adjusted body weight; aminoglycosides have poor adipose tissue penetration.
* **Infusion:** Administer over 30–60 minutes.
* **Efficacy:** Concentration-dependent killing implies higher peaks relative to the Minimum Inhibitory Concentration (MIC) correlate with better outcomes.
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**Disclaimer:** This information is for educational purposes only. Drug protocols, renal dosing nomograms, and institutional criteria vary significantly. Always verify specific institutional protocols and current prescribing information (e.g., FDA-approved package insert) before clinical application.
