A 78-year-old woman with a history of chronic kidney disease (CKD stage 3b, baseline creatinine 2.1 mg/dL, eGFR ~35 mL/min), atrial fibrillation (on amiodarone), and type 2 diabetes mellitus presents to her primary care physician with a three-day history of dysuria, increased urinary frequency, and mild suprapubic discomfort. She denies fever, flank pain, nausea, or vomiting.
Initial Workup:
- Urinalysis: Positive for leukocyte esterase, nitrites, pyuria, and bacteriuria
- Urine culture: Grows Escherichia coli (pan-sensitive)
- Serum creatinine: 2.1 mg/dL (baseline), eGFR ~35 mL/min
Given her clinical presentation, she is diagnosed with an uncomplicated cystitis and requires an appropriate oral antibiotic
Question:
Which of the following antibiotics is the best choice for treating this patient’s cystitis?
A) Oral nitrofurantoin (Macrobid)
B) Oral trimethoprim-sulfamethoxazole (Bactrim)
C) Oral fosfomycin
D) Oral cefdinir
E) Oral ciprofloxacin
Correct Answers:
✅ C) Oral Fosfomycin
✅ D) Oral Cefdinir
Why Fosfomycin or Cefdinir Are Good Choices:
Both are safe in CKD
- Fosfomycin: No renal adjustment needed, well tolerated.
- Cefdinir: Requires renal dose adjustment in CKD, but remains a good oral cephalosporin option for UTIs.
Both provide excellent activity against E. coli
- Fosfomycin is bactericidal and effective for uncomplicated cystitis.
- Cefdinir achieves high urinary concentrations, making it effective in uncomplicated UTIs.
Differences in Dosing and Convenience:
- Fosfomycin (Single 3g dose) is most convenient but may not be suitable if longer therapy is needed (e.g., recurrent UTIs).
- Cefdinir (300 mg BID for 5 days) requires multiple doses but is widely available and well tolerated.
Both avoid major drug interactions with amiodarone.
Why Other Options Are Incorrect:
A) Nitrofurantoin (Macrobid) ❌
๐ซ Contraindicated in CKD with eGFR <30 mL/min due to poor urinary concentration.B) Trimethoprim-Sulfamethoxazole (Bactrim) ❌
๐ซ Nephrotoxic and increases hyperkalemia risk in CKD.E) Ciprofloxacin (Fluoroquinolone) ❌
๐ซ Not first-line for uncomplicated cystitis due to increasing resistance and risk of adverse effects (QT prolongation, tendinopathy).
๐ซ Interacts with amiodarone (QT prolongation, cardiac arrhythmias).
Key Takeaways:
- Fosfomycin is the most convenient option (single-dose), while cefdinir is a great multi-dose alternative for uncomplicated cystitis.
- Cefdinir is an appropriate cephalosporin choice for UTIs when renal function is impaired and fosfomycin is unavailable.
- Bactrim and nitrofurantoin should be avoided in CKD due to nephrotoxicity and poor efficacy, respectively.
- Ciprofloxacin is NOT first-line due to increasing resistance and side effects.
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