What injectable antibiotics, such as (intravenous) cephalosporins (e.g. ceftriaxone or cefotaxime) or aminoglycosides (e.g. gentamicin or tobramycin), can be given to adult patients with a confirmed diagnosis of a urinary tract infection (UTI)?

Injectable Antibiotics for UTI Patients

Ceftriaxone 1-2 g IV daily is the recommended first-line injectable antibiotic for adult patients with UTI requiring intravenous therapy, based on its low resistance rates, clinical effectiveness, and once-daily dosing convenience. 1

First-Line Injectable Options for Uncomplicated Pyelonephritis

Third-generation cephalosporins:

• Ceftriaxone 1-2 g IV once daily is the preferred agent due to proven efficacy and favorable resistance patterns 1
• Cefotaxime 2 g IV three times daily is an alternative third-generation cephalosporin, though not as extensively studied as monotherapy 1, 2
• Cefepime 1-2 g IV twice daily (fourth-generation cephalosporin) provides broader coverage 1

Fluoroquinolones (if local resistance <10%):

• Ciprofloxacin 400 mg IV twice daily 1
• Levofloxacin 750 mg IV once daily 1

Aminoglycosides:

• Gentamicin 5 mg/kg IV once daily (not studied as monotherapy but effective when combined with ampicillin) 1
• Amikacin 15 mg/kg IV once daily 1

Extended-spectrum penicillins:

• Piperacillin-tazobactam 2.5-4.5 g IV three times daily 1

Injectable Options for Complicated UTI

For complicated UTI with risk factors for multidrug-resistant organisms, broader-spectrum agents are warranted:

Novel beta-lactam/beta-lactamase inhibitor combinations:

• Ceftazidime-avibactam 2.5 g IV every 8 hours (for CRE and ESBL-producing organisms) 1
• Meropenem-vaborbactam 4 g IV every 8 hours (for CRE with KPC carbapenemases) 1
• Imipenem-cilastatin-relebactam 1.25 g IV every 6 hours (for CRE) 1
• Ceftolozane-tazobactam 1.5 g IV three times daily (for Pseudomonas and ESBL organisms) 1, 3

Carbapenems (reserve for documented multidrug-resistant organisms):

• Meropenem 1 g IV three times daily 1
• Imipenem-cilastatin 0.5 g IV three times daily 1

Novel agents for highly resistant organisms:

• Cefiderocol 2 g IV three times daily (for carbapenem-resistant organisms) 1, 3
• Plazomicin 15 mg/kg IV every 12 hours (for CRE) 1

Pediatric Injectable Regimens

For newborns and infants:

• Parenteral ampicillin PLUS aminoglycoside OR third-generation cephalosporin 1

For children <6 months with pyelonephritis:

• Ceftazidime plus ampicillin, OR aminoglycoside plus ampicillin 1

For children >6 months with uncomplicated pyelonephritis:

• Third-generation cephalosporin (ceftriaxone preferred) 1

For complicated pyelonephritis (all ages):

• Ceftazidime plus ampicillin, OR aminoglycoside plus ampicillin 1

Critical Decision-Making Algorithm

Step 1: Assess UTI severity and complications

• Uncomplicated pyelonephritis → Ceftriaxone 1-2 g IV daily 1
• Complicated UTI without MDR risk → Ceftriaxone or piperacillin-tazobactam 1
• Complicated UTI with MDR risk factors → Novel beta-lactam combinations or carbapenems 1

Step 2: Consider local resistance patterns

• Use ceftriaxone only if local ESBL rates are acceptable 1
• Fluoroquinolones should only be used if local resistance <10% 1
• Reserve carbapenems and novel agents for documented resistance 1

Step 3: Adjust for patient-specific factors

• Antipseudomonal agents (ceftazidime-avibactam, ceftolozane-tazobactam) only for nosocomial pathogen risk 1, 3
• Carbapenem therapy empirically reasonable in patients with prior ESBL or CRE colonization 1

Treatment Duration

For pyelonephritis:

• Beta-lactams: 7 days 1
• Fluoroquinolones: 5-7 days 1
• Aminoglycosides: Duration unclear, but single-dose or short-course may be effective 1

For gram-negative bacteremia from urinary source:

• 7 days total duration 1

Important Caveats

Avoid these common pitfalls:

• Do not use aminoglycosides as monotherapy for pyelonephritis without supporting evidence, though observational data suggest single-dose may achieve high cure rates 1
• Ceftriaxone doubles the risk of hospital-onset Clostridioides difficile infection compared to first-generation cephalosporins, but remains preferred for pyelonephritis requiring IV therapy 4
• Reserve broad-spectrum agents (carbapenems, novel combinations) strictly for documented multidrug-resistant organisms to prevent further resistance development 1, 3
• Fluoroquinolones should be avoided as first-line due to rising resistance and collateral damage concerns unless no alternatives exist 1