A 68-year-old man with community-acquired pneumonia and renal impairment (creatinine 2.2 mg/dL) is prescribed gentamicin. Regarding aminoglycoside toxicity and monitoring, all of the following are true EXCEPT:

Explanation

## Aminoglycoside Toxicity and Dose Adjustment in Renal Impairment ### Overview of Aminoglycoside Toxicity **High-Yield:** Aminoglycosides cause two major toxicities — nephrotoxicity and ototoxicity — both related to drug accumulation. Renal impairment dramatically increases the risk of both. ### Nephrotoxicity **Key Point:** Aminoglycoside-induced acute tubular necrosis (ATN) is: - **Dose-dependent and reversible** if caught early and the drug is stopped - More common with prolonged therapy (>7–10 days) - Worsened by concurrent nephrotoxins: NSAIDs, ACE inhibitors, amphotericin B, cisplatin - Incidence: 5–10% with conventional dosing; <1% with once-daily dosing **Clinical Pearl:** Monitor serum creatinine and urine output closely. If creatinine rises >0.5 mg/dL above baseline or urine output drops, consider discontinuation. ### Ototoxicity **Key Point:** Aminoglycoside ototoxicity is: - **Irreversible** (permanent hearing loss) - Dose-dependent, cumulative, and related to high trough levels - Manifests first as **high-frequency hearing loss** (>4 kHz), progressing to lower frequencies - Risk factors: prolonged therapy, renal impairment, concurrent loop diuretics, advanced age **Mnemonic:** **OTOTOXIC** — **O**lder age, **T**otal dose, **O**ther ototoxins (loop diuretics), **T**rough levels high, **O**ther nephrotoxins, **X**tended duration, **I**mpaired renal function, **C**umulative effect. ### Dose Adjustment in Renal Impairment **Key Point:** Aminoglycosides are **NOT metabolized by the liver** — they are eliminated **unchanged by the kidneys** (>90%). In renal impairment, dose adjustment is **MANDATORY**. | Creatinine Clearance | Dosing Strategy | | --- | --- | | >60 mL/min | Standard dosing | | 40–60 mL/min | Reduce dose or extend interval | | 20–40 mL/min | Significant reduction; once-daily preferred | | <20 mL/min | Avoid or use extended-interval dosing (e.g., 7 mg/kg Q24–48h) | | Dialysis patients | Dose after dialysis; monitor levels | **Warning:** Giving standard doses in renal impairment leads to drug accumulation, increased trough levels, and higher risk of nephrotoxicity and irreversible ototoxicity. ### Why Option 4 Is Wrong **High-Yield:** This statement is **FALSE**. Aminoglycosides are: - **NOT metabolized by the liver** — they are eliminated unchanged by glomerular filtration - **Contraindicated or require major dose reduction** in renal impairment - A common NEET PG trap: confusing aminoglycosides (renally eliminated) with macrolides or fluoroquinolones (hepatically metabolized) ## Comparison: Nephrotoxicity vs. Ototoxicity | Feature | Nephrotoxicity | Ototoxicity | | --- | --- | --- | | Reversibility | Yes (if early) | No (irreversible) | | Mechanism | Proximal tubular uptake → ATN | Cochlear/vestibular damage | | Peak vs. Trough | Trough-dependent | Trough-dependent | | Onset | Days to weeks | Weeks to months | | Monitoring | Creatinine, BUN | Audiometry, high-frequency hearing | | Prevention | Reduce dose in renal failure | Once-daily dosing, avoid loop diuretics | [cite:KD Tripathi 8e Ch 46; Harrison 21e Ch 163]