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# IV Gentamicin
## Overview
Gentamicin is an aminoglycoside antibiotic that exerts bactericidal activity by irreversibly binding to the 30S ribosomal subunit, inhibiting protein synthesis. It provides excellent coverage against aerobic gram-negative bacilli, including *Pseudomonas aeruginosa*.
## Primary Indications
* Serious gram-negative infections (e.g., sepsis, complicated UTI, pneumonia).
* Synergistic coverage for gram-positive endocarditis (e.g., *Staphylococcus* or *Enterococcus* species).
## Adult Dosing
* **Traditional Dosing:** 1–2.5 mg/kg every 8–12 hours.
* **Extended Interval Dosing (EID):** 5–7 mg/kg every 24 hours (based on nomograms like Hartford).
* **Synergy Dosing (Endocarditis):** 1 mg/kg every 8 hours.
* **Maximum:** Dosing must be weight-based; clinical ceilings vary by institution and renal function.
## Pediatric Dosing
* **Neonates (Preterm):** 2.5–4 mg/kg every 24–48 hours (highly dependent on gestational age).
* **Neonates (Term):** 4 mg/kg every 24 hours.
* **Infants/Children:** 2.5 mg/kg every 8 hours (traditional) or 5–7.5 mg/kg once daily (EID, institutional protocol dependent).
## Dose Adjustments
* **Renal Impairment:** Reduce frequency or dose based on measured or estimated CrCl.
* **Obesity:** Use Adjusted Body Weight (IBW + 0.4 × [TBW - IBW]) for dosing calculations to avoid toxicity.
* **Dialysis:** Requires post-dialysis dosing; pharmacists should calculate based on specific dialysis clearance rates.
## Contraindications
* Hypersensitivity to aminoglycosides.
* History of severe reaction to any aminoglycoside.
## Adverse Effects
* **Nephrotoxicity:** Usually reversible; related to trough levels and duration of therapy.
* **Ototoxicity:** Auditory (hearing loss) or vestibular (vertigo); often irreversible.
* **Neuromuscular Blockade:** Rare, but potential risk in patients with myasthenia gravis.
## Key Drug Interactions
* **Nephrotoxic agents:** Increased risk with vancomycin, amphotericin B, NSAIDs, and loop diuretics (e.g., furosemide).
* **Neuromuscular blockers:** May potentiate paralysis.
## Monitoring
* **Renal Function:** Daily Scr and urine output.
* **Serum Concentrations:**
* *Traditional:* Trough levels (obtained 30 minutes before the 3rd or 4th dose).
* *EID:* Random level 6–14 hours after the start of infusion (plotted on a nomogram).
* **Toxicity:** Audiometry/vestibular assessments if therapy duration > 7 days.
## Clinical Pearls
* Gentamicin has a post-antibiotic effect (PAE); this is the primary rationale for once-daily (extended-interval) dosing.
* Avoid prolonged therapy (> 10–14 days) to minimize cumulative toxicity.
* Verify institutional specific protocols, as nomograms for EID vary significantly between facilities.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice guidelines and local institutional protocols should always be verified before prescribing or administering medication. Consult the most current drug monographs and your pharmacy department for the latest safety information and dosing adjustments.
