A 60‑year‑old woman with cystitis is treated with amoxicillin but symptoms persist. Urine culture shows β‑lactamase–producing Klebsiella pneumoniae. Suggest a second‑line oral antibiotic and justify the choice based on mechanism of action and resistance profile.
Answer
Ciprofloxacin 500 mg twice daily for 7 days, because fluoroquinolones inhibit bacterial DNA gyrase and are effective against β‑lactamase producing gram‑negative organisms.
Step-by-step solution
- Identify the causative organism as Klebsiella pneumoniae
- Recognise that it produces β‑lactamase and is resistant to amoxicillin
- Choose an antibiotic class not affected by β‑lactamase (fluoroquinolones)
- Select ciprofloxacin 500 mg bid for 7 days
- Explain that fluoroquinolones inhibit DNA gyrase, killing the bacteria
Common mistake: Choosing β‑lactam antibiotics despite β‑lactamase production
Concept tested: Antibiotic resistance management
Published · How this solution was prepared and checked
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