For a 73‑year‑old woman with a complicated urinary tract infection, whose culture is susceptible only to levofloxacin (resistant to trimethoprim‑sulfamethoxazole (Bactrim) and fosfomycin) and who has a nitrofurantoin (nitrofuran) allergy, what levofloxacin dose and treatment duration is appropriate?

Levofloxacin 750 mg Once Daily for 5–7 Days Is the Appropriate Regimen for This Patient

For a 73-year-old woman with a complicated urinary tract infection whose culture shows susceptibility only to levofloxacin (with resistance to trimethoprim-sulfamethoxazole and fosfomycin) and who has a nitrofurantoin allergy, levofloxacin 750 mg orally once daily for 5–7 days is the evidence-based treatment of choice. 1, 2

Rationale for Levofloxacin 750 mg Once Daily

• The FDA-approved indication for levofloxacin 750 mg once daily specifically includes complicated urinary tract infections, with a 5-day regimen approved for infections due to E. coli, Klebsiella pneumoniae, or Proteus mirabilis. 2

• The 2011 IDSA/ESCMID guideline explicitly recommends levofloxacin 750 mg once daily for 5 days as an appropriate choice for pyelonephritis and complicated UTIs in patients not requiring hospitalization, provided local fluoroquinolone resistance does not exceed 10%. 3

• High-dose, short-course levofloxacin (750 mg for 5 days) has been proven noninferior to 10-day ciprofloxacin regimens in randomized controlled trials, with microbiologic eradication rates of 83% in the modified intent-to-treat population and 92.5% in the microbiologically evaluable population. 4

Treatment Duration: 5 Days vs. 7 Days

• A 5-day course is sufficient when the patient achieves prompt symptom resolution, remains afebrile for ≥48 hours, and is hemodynamically stable. 1

• Extend therapy to 7 days if there is delayed clinical response, persistent fever beyond 72 hours, or evidence of upper-tract involvement (pyelonephritis). 1

• In elderly patients (≥73 years), age alone classifies the UTI as complicated, but this does not automatically mandate a longer duration—clinical response determines whether 5 or 7 days is appropriate. 1

Why Alternative Agents Are Inappropriate in This Case

• Trimethoprim-sulfamethoxazole is contraindicated because the susceptibility report shows resistance (indicated by "zero" on the report). 3

• Fosfomycin is also resistant based on the susceptibility report ("zero and a plus or minus"), and it is explicitly not recommended for complicated UTIs due to inadequate tissue penetration. 1

• Nitrofurantoin is contraindicated due to the patient's documented allergy (nitrofuran allergy), and it is unsuitable for complicated UTIs or upper-tract involvement regardless. 1, 5

• Oral β-lactam agents (e.g., cephalosporins, amoxicillin-clavulanate) are markedly less effective than fluoroquinolones for complicated UTIs, with failure rates 15–30% higher, and should only be used when fluoroquinolones are unavailable or contraindicated. 3, 1

Critical Pre-Treatment and Monitoring Steps

• Confirm that a urine culture with susceptibility testing was obtained before initiating therapy, as this is mandatory for all complicated UTIs to guide targeted treatment. 3, 1

• Assess for underlying urological complications (obstruction, incomplete bladder emptying, indwelling catheter) that may require source control in addition to antibiotics. 1

• Reassess the patient at 72 hours if there is no clinical improvement with defervescence; lack of progress warrants extension of therapy, urologic evaluation, or consideration of alternative diagnoses. 1

Common Pitfalls to Avoid

• Do not use the 500 mg dose of levofloxacin for a 5-day regimen; the 750 mg dose is required to achieve the pharmacodynamic targets necessary for efficacy in complicated UTIs. 1, 6

• Do not extend therapy to 14 days unless there is documented delayed clinical response or inability to exclude upper-tract involvement; the 14-day duration is reserved for males when prostatitis cannot be excluded or for patients with persistent symptoms. 3, 1

• Do not use fluoroquinolones empirically if local resistance exceeds 10% or if the patient has recent fluoroquinolone exposure, but in this case susceptibility is documented on culture, making levofloxacin appropriate. 3, 1

• Do not treat asymptomatic bacteriuria after completing therapy; follow-up urine cultures are only indicated if symptoms persist or recur. 1

Antimicrobial Stewardship Considerations

• The high-dose, short-course levofloxacin regimen (750 mg for 5 days) reduces total antibiotic exposure compared to 10-day regimens, thereby decreasing collateral damage to normal flora and selection pressure for resistance while maintaining equivalent efficacy. 6, 4

• Fluoroquinolones should be reserved for situations where first-line agents cannot be used due to allergy or resistance, which applies to this patient given her nitrofurantoin allergy and documented resistance to trimethoprim-sulfamethoxazole and fosfomycin. 5