A 62-year-old man with diabetes mellitus presents with fever, dysuria, and flank pain. Urine culture grows Gram-negative rods. He has normal renal function (creatinine 0.9 mg/dL). Which aminoglycoside is the drug of choice for empirical therapy of this uncomplicated pyelonephritis?

Explanation

## Aminoglycoside Selection in Pyelonephritis **Key Point:** Gentamicin is the first-line aminoglycoside for uncomplicated pyelonephritis caused by susceptible Gram-negative organisms in patients with normal renal function. ### Rationale for Gentamicin **High-Yield:** Gentamicin is preferred because: 1. Excellent activity against *E. coli*, *Klebsiella*, and *Proteus* (common uropathogens) 2. Achieves high urinary and renal parenchymal concentrations 3. Cost-effective compared to broader-spectrum agents 4. Once-daily dosing (5–7 mg/kg IV/IM) is nephrotoxic and ototoxic in <5% of patients with normal baseline renal function 5. Predictable pharmacokinetics in this patient (normal creatinine) ### Aminoglycoside Spectrum & Clinical Use Hierarchy | Aminoglycoside | First-line Use | Key Limitation | Notes | | --- | --- | --- | --- | | **Gentamicin** | Uncomplicated UTI/pyelonephritis, empirical Gram-negative sepsis | Resistance in *Pseudomonas* (30–40%) | Preferred in susceptible infections | | **Amikacin** | *Pseudomonas aeruginosa*, resistant Gram-negatives, empirical nosocomial infection | Broader spectrum = overuse risk | Reserved for resistant organisms | | **Tobramycin** | *Pseudomonas aeruginosa* (especially in CF) | Limited Gram-positive activity | Preferred for *Pseudomonas* over gentamicin | | **Netilmicin** | Resistant Gram-negatives | Minimal advantage over amikacin | Rarely used in India | **Clinical Pearl:** In uncomplicated community-acquired pyelonephritis with normal renal function and no prior aminoglycoside exposure, gentamicin is cost-effective and has excellent clinical outcomes. Reserve amikacin for suspected resistance or nosocomial infection. **Mnemonic — Aminoglycoside Selection:** **GENT** for **GEN**eral/community infections; **AMIK** for **AMIK**acin-resistant or nosocomial. ### Dosing in Normal Renal Function - Gentamicin: 5–7 mg/kg once daily IV/IM (preferred over 3 times daily) - Monitor: Serum creatinine at baseline and day 3–5; peak/trough levels if prolonged therapy (>7 days) **Warning:** Do NOT use amikacin as first-line in uncomplicated infections — this promotes resistance and increases cost without clinical benefit.