Acute Pyelonephritis with possible Bacteraemia

Scenario:
A 35‑year‑old woman with a history of recurrent urinary tract infections presents to the ED with a 2‑day history of high fever (39.5 °C), chills, nausea, and severe left flank pain. On exam she is tachycardic (120 bpm), hypotensive (BP 90/55 mmHg), and appears unwell. Costovertebral angle tenderness is present on the left. Urine dipstick is positive for nitrites and leukocyte esterase. You draw blood and urine cultures; initial Gram stain of the blood cultures shows gram‑negative rods.

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Question:
Which of the following is the best empiric IV antibiotic for this patient?

A) Ceftriaxone
B) Cefepime
C) Aztreonam
D) Piperacillin–tazobactam (Zosyn)
E) Meropenem

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✅ Preferred Answer: E) Meropenem

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📘 Mini‑Lesson & Explanation

1. Meropenem (E) – Why It’s Best

   • Broad-spectrum: Covers ESBL‑producing Enterobacterales and Pseudomonas spp.

   • Bacteraemic urinary sepsis: Ensures prompt bacterial clearance in severe cases.

   • Stable in vitro: Active against most resistant gram‑negative rods you might encounter in recurrent UTIs.

2. Why Not Ceftriaxone (A)?

   • Good for typical community Gram‑negatives but no Pseudomonas coverage and inactive against ESBL‑producers.

   • In recurrent UTIs, risk of resistance is higher.

3. Why Not Cefepime (B)?

   • Excellent Pseudomonas coverage but limited activity against ESBL organisms.

   • May fail if ESBL risk is significant.

4. Why Not Aztreonam (C)?

   • Covers Pseudomonas and other Gram‑negatives, but like cefepime lacks ESBL activity.

   • Often reserved for β‑lactam–allergic patients.

5. Why Not Piperacillin–Tazobactam (D)?

   • Broad Gram‑negative and anaerobic coverage, including Pseudomonas, but inconsistent activity against some ESBLs.

   • Also increases risk of Clostridioides difficile infection.

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💡 Teaching Pearls

• Recurrent UTIs = Resistance Risk: Always consider ESBL‑producers in patients with frequent antibiotic exposure or recurrent infections.

• Empiric Choice for Severe Sepsis: In urosepsis with bacteraemia, a carbapenem is the safest empiric bet when ESBL risk is high.

• Stewardship Note: Once cultures and susceptibilities return, de‑escalate to a narrower agent if possible (e.g., ceftriaxone for susceptible E. coli).

• When to Use Alternatives:

• Cefepime or Zosyn if ESBL risk is low and you need Pseudomonas coverage.

• Aztreonam in severe β‑lactam allergy<table>

    

Antibiotic	Gram‑negative Coverage	Pseudomonas Coverage	ESBL Activity	Notes
Ceftriaxone	Good	No	No	Excellent for community Enterobacterales
Cefepime	Very good	Yes	Limited	Good for nosocomial GNRs, but not ESBL‑producers
Ceftazidime	Very good	Yes	Limited	Excellent for Pseudomonas; limited ESBL activity; no anaerobes
Aztreonam	Good	Yes	No	Safe in penicillin/cephalosporin allergy
Piperacillin–Tazobactam	Very good	Yes	Variable	Broad GNR + anaerobe; inconsistent vs ESBL
Meropenem	Excellent	Yes	Yes	Carbapenem of choice for ESBL and MDR GNRs