Recommended IV Antibiotics for Severe or Complicated UTI
For severe or complicated UTIs, initiate IV therapy with extended-spectrum cephalosporins (ceftriaxone 1-2 g daily or cefepime 1-2 g every 12 hours), fluoroquinolones (ciprofloxacin 400 mg every 12 hours or levofloxacin 750 mg daily), or aminoglycosides (gentamicin 5-7 mg/kg daily or amikacin 15 mg/kg daily), with treatment duration of 7-10 days for most cases. 1
First-Line IV Antibiotic Options
Extended-Spectrum Cephalosporins
- Ceftriaxone 1-2 g IV daily is a preferred first-line agent due to once-daily dosing convenience and broad coverage against common uropathogens including E. coli and Klebsiella pneumoniae 2, 1
- Cefepime 1-2 g IV every 12 hours provides excellent coverage, with the FDA specifically approving it for severe uncomplicated or complicated UTIs including pyelonephritis 3
- For Pseudomonas aeruginosa infections, increase cefepime to 2 g IV every 8 hours 4, 3
- Cefazolin 1 g IV every 8 hours is an alternative for standard complicated UTIs when broader coverage is not required 2
Fluoroquinolones
- Ciprofloxacin 400 mg IV every 12 hours or levofloxacin 750 mg IV daily are effective options 2, 1
- Only use fluoroquinolones empirically when local resistance rates are less than 10% 1
- Avoid in patients with recent fluoroquinolone exposure due to resistance concerns 1
Aminoglycosides
- Gentamicin 5-7 mg/kg IV once daily is particularly valuable when fluoroquinolone resistance is documented 2, 1
- Amikacin 15 mg/kg IV once daily provides broader coverage against aminoglycoside-resistant organisms 1
- Critical caveat: Aminoglycoside monotherapy should only be used for urinary tract infections, not for systemic infections or bacteremia 2
Treatment Duration
- Standard complicated UTIs: 7-10 days 1, 3
- With concurrent bacteremia: Extend to 10-14 days 4, 1
- Men when prostatitis cannot be excluded: 14 days mandatory 1
- Hemodynamically stable patients afebrile for ≥48 hours: 7 days acceptable 1
Multidrug-Resistant Organisms
For Carbapenem-Resistant Enterobacterales (CRE)
- Ceftazidime-avibactam 2.5 g IV every 8 hours 2, 1
- Meropenem-vaborbactam 4 g IV every 8 hours 2, 1
- Imipenem/cilastatin/relebactam 1.25 g IV every 6 hours 1
- Plazomicin 15 mg/kg IV every 12 hours specifically for CRE, with demonstrated lower mortality (24% vs 50%) and reduced acute kidney injury (16.7% vs 50%) compared to colistin-based regimens 1
For Difficult-to-Treat Pseudomonas
- Ceftolozane/tazobactam 1.5-3 g IV every 8 hours 2, 4
- Ceftazidime/avibactam 2.5 g IV every 8 hours 2, 4
Critical Management Principles
Before Initiating Therapy
- Obtain urine culture and antimicrobial susceptibility testing in all cases of pyelonephritis and complicated UTIs 4, 1
- Base empiric antibiotic choice on local resistance patterns 2, 1
Source Control
- Ensure adequate source control including relief of obstruction and removal of foreign bodies (e.g., catheters, stones) for optimal treatment outcomes 2
- Without source control, even appropriate antibiotics may fail
Monitoring
- Assess for clinical improvement within 48-72 hours 1
- Consider follow-up urine culture after therapy completion to confirm eradication, especially in complicated cases 4, 1
Renal Dose Adjustments
Cefepime (FDA-approved dosing)
- CrCl 30-60 mL/min: Reduce to every 24 hours or 2 g every 12 hours depending on severity 3
- CrCl 11-29 mL/min: 500 mg to 2 g every 24 hours depending on severity 3
- CrCl <11 mL/min: 250 mg to 1 g every 24 hours 3
- Hemodialysis: 1 g on day 1, then 500 mg every 24 hours; administer after dialysis 3
Cefazolin
Common Pitfalls to Avoid
- Do not use aminoglycoside monotherapy for bacteremia or systemic infection—reserve for isolated UTI only 2
- Do not delay source control measures while waiting for antibiotic effect 2
- Do not use fluoroquinolones empirically in areas with >10% resistance or in patients with recent exposure 1
- Do not forget to adjust doses for renal impairment—cephalosporins and aminoglycosides require careful dose modification 2, 3