A 58-year-old man with diabetes mellitus and chronic kidney disease (eGFR 35 mL/min/1.73m²) is admitted with urosepsis due to Pseudomonas aeruginosa. Blood cultures are positive. He is started on piperacillin-tazobactam and gentamicin. After 48 hours, serum creatinine rises from 2.1 to 2.8 mg/dL, and urine output drops to 0.3 mL/kg/hr. Gentamicin peak and trough levels are 8 µg/mL and 2.2 µg/mL respectively. What is the most appropriate next step in management?

Explanation

## Clinical Assessment This patient has clear evidence of **aminoglycoside-induced acute kidney injury (AKI)**: - Rising serum creatinine (2.1 → 2.8 mg/dL in 48 hours) - Oliguria (0.3 mL/kg/hr) - Pre-existing risk factors: diabetes, CKD (eGFR 35), age >50 - Gentamicin trough level 2.2 µg/mL is suboptimal but not the primary issue **Key Point:** Aminoglycoside nephrotoxicity is **dose- and duration-dependent**. Once clinical AKI develops (rising creatinine + oliguria), continued exposure risks irreversible renal failure. The risk is highest in patients with pre-existing renal impairment, and this patient should never have received standard-dose gentamicin without aggressive renal dosing from the outset. ## Why Discontinuation Is Correct **High-Yield:** Once aminoglycoside-induced AKI is documented: 1. **Discontinue the offending agent immediately** — further exposure worsens injury 2. **Switch to a non-nephrotoxic alternative** — fluoroquinolones (levofloxacin) or carbapenems (meropenem) or aztreonam are appropriate for Pseudomonas coverage 3. **Supportive care** — aggressive fluid resuscitation, electrolyte management, renal replacement therapy if needed **Clinical Pearl:** Aminoglycoside nephrotoxicity is **partially reversible** if caught early and the drug is stopped. However, continued use after AKI develops significantly increases the risk of permanent renal dysfunction. In a septic patient with documented AKI, the risk of progression outweighs any marginal benefit from continued aminoglycoside therapy. ## Mechanism of Aminoglycoside Nephrotoxicity **Key Point:** Aminoglycosides accumulate in the proximal tubule via endocytosis and cause: - Mitochondrial dysfunction - Reactive oxygen species generation - Tubular epithelial cell necrosis - Non-oliguric or oliguric AKI (typically reversible if caught early) Risk factors include: - Pre-existing renal disease (this patient: eGFR 35) - Diabetes mellitus (this patient: present) - Age >50 years (this patient: 58) - Volume depletion - Concurrent nephrotoxic agents - Prolonged therapy (>7–10 days) ## Why Other Options Are Wrong | Option | Rationale | |--------|----------| | Continue same dose | Dangerous; AKI is already present and will worsen with continued exposure | | Reduce dose/extend interval | Dose reduction alone does not address the acute tubular injury already occurring; discontinuation is safer | | Increase dose | Contraindicated; higher doses accelerate nephrotoxicity and worsen AKI | **Mnemonic:** **STOP AMINO** when AKI develops: - **S**witch to alternative agent - **T**erminate aminoglycoside immediately - **O**ptimize fluid status and electrolytes - **P**rovide supportive care ± RRT - **A**void re-exposure - **M**onitor renal recovery - **I**nvestigate other causes of AKI - **N**ephrology consultation if creatinine does not stabilize - **O**ffer renal replacement therapy if indicated ## Summary **The correct next step is to discontinue gentamicin and switch to a non-nephrotoxic alternative** (fluoroquinolone, aztreonam, or carbapenem) because aminoglycoside-induced AKI is progressive and irreversible if exposure continues. Dose reduction or continued monitoring are inadequate once clinical AKI is evident.