In a patient with a urinary tract infection who was started on ciprofloxacin and then prescribed cefalexin, and whose culture shows susceptibility to both agents, which antibiotic should be continued?

Continue Ciprofloxacin and Discontinue Cephalexin

The patient should continue ciprofloxacin and stop cephalexin. Given that the organism is susceptible to both antibiotics, ciprofloxacin is the superior choice based on established efficacy data, and there is no clinical benefit to switching to or adding cephalexin.

Rationale Based on Guidelines and Evidence

Ciprofloxacin is the Preferred Agent

The IDSA/ESMID guidelines clearly establish that ciprofloxacin (500 mg twice daily for 7 days) is an appropriate first-line choice for UTI treatment when the organism is susceptible 1. Your culture confirms susceptibility to ciprofloxacin, validating your initial empiric choice.

Cephalexin Has Inferior Efficacy

The same guidelines explicitly state that β-lactams such as cephalexin are "less well studied" and have "inferior efficacy and more adverse effects compared with other UTI antimicrobials" 1. The guidelines recommend β-lactams "should be used with caution for uncomplicated cystitis" and only "when other recommended agents cannot be used" 1.

Direct comparative data supports this: a randomized trial showed ciprofloxacin achieved significantly better outcomes than cephalexin for lower UTI, with ciprofloxacin demonstrating "convincingly better clinical and bacteriological efficacy" 2.

No Advantage to Switching or Combining

Since you've already initiated ciprofloxacin and the organism is susceptible:

• Switching to cephalexin would be a step down to a less effective agent with no clinical justification
• There is no role for combination therapy when a single effective agent is available
• The patient has already started the superior antibiotic

Clinical Severity Considerations

If this is uncomplicated cystitis: Ciprofloxacin 500 mg twice daily for 3 days is sufficient 1

If this is pyelonephritis or complicated UTI: Continue ciprofloxacin 500 mg twice daily for 7 days 1

Common Pitfalls to Avoid

• Don't assume "newer prescription = better prescription" - The urgent care provider may not have had access to your treatment history or may have reflexively prescribed a β-lactam
• Don't combine antibiotics unnecessarily - This increases adverse effects, costs, and resistance pressure without improving outcomes when a single susceptible agent exists
• Don't switch to a less effective agent mid-course - This violates antimicrobial stewardship principles

Practical Action Steps

1. Contact the patient immediately to clarify they should continue only ciprofloxacin
2. Verify the clinical syndrome (cystitis vs pyelonephritis) to determine appropriate duration (3 vs 7 days)
3. Document the rationale in the medical record to prevent future confusion
4. Consider notifying the urgent care about the duplicate/conflicting prescription to improve care coordination

The culture results validate your initial choice - there is no reason to deviate from effective therapy already in progress.