What antibiotic is effective against gram-negative rods in a patient's urine?

Treatment of Gram-Negative Rods in Urine

For urinary tract infections caused by gram-negative rods, fluoroquinolones (ciprofloxacin 500 mg twice daily or levofloxacin 750 mg once daily) are first-line agents for complicated UTIs, while nitrofurantoin, fosfomycin, or trimethoprim-sulfamethoxazole are appropriate for uncomplicated lower UTIs when susceptibility is confirmed. 1, 2

Antibiotic Selection Based on Clinical Presentation

For Uncomplicated Lower UTI (Cystitis)

• Nitrofurantoin is a first-line option for uncomplicated cystitis, typically given for 5 days 3
• Fosfomycin 3g single dose is highly effective for uncomplicated lower UTI 3
• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3-5 days remains effective when local resistance rates are <20% 2, 3

For Complicated UTI or Pyelonephritis

• Fluoroquinolones are the preferred oral agents: Ciprofloxacin 500 mg twice daily for 7 days or levofloxacin 750 mg once daily for 5-7 days 1, 4, 5
• Dose-optimized β-lactams for 7 days are appropriate alternatives 1
• For patients requiring IV therapy initially, ceftriaxone 1g IV followed by oral step-down once stable is recommended 2

For Severe Infections Requiring Parenteral Therapy

• Ciprofloxacin 400 mg IV twice daily or levofloxacin 750 mg IV daily for patients with septic shock or inability to tolerate oral medications 4
• Aminoglycosides (gentamicin 5 mg/kg daily) can be used for short-duration therapy (≤7 days) in hospitalized patients without shock 4, 6
• Piperacillin-tazobactam or cefepime are appropriate for severe infections, reserving carbapenems for multidrug-resistant organisms 4

Treatment Duration

• Uncomplicated cystitis: 3-5 days depending on agent used 1, 2
• Pyelonephritis: 5-7 days with fluoroquinolones; 14 days if using trimethoprim-sulfamethoxazole 1, 2
• Complicated UTI: 7 days minimum, extending to 10-14 days based on clinical response 1, 4
• Gram-negative bacteremia from urinary source: 7 days total when source control achieved 1
• Catheter-associated UTI (CAUTI): 5-7 days with catheter exchange/removal 1

Resistance Considerations and Drug Selection

For Extended-Spectrum β-Lactamase (ESBL) Producers

• Carbapenems (meropenem, imipenem) are preferred for severe infections 1
• Nitrofurantoin and fosfomycin remain effective for uncomplicated lower UTI caused by ESBL-producing E. coli 3
• Avoid cephalosporins and piperacillin-tazobactam even if susceptible in vitro, as clinical outcomes are poor 1

For Non-Lactose Fermenting Organisms (Pseudomonas, Acinetobacter)

• Ciprofloxacin 500 mg twice daily or levofloxacin 750 mg once daily are first-line oral options 4, 7
• For severe infections, ceftazidime, cefepime, or piperacillin-tazobactam are appropriate 3
• Never use fosfomycin for non-fermenting organisms—it is restricted to typical uropathogens only 4

Critical Pitfalls to Avoid

• Do NOT use nitrofurantoin or fosfomycin for pyelonephritis or complicated UTI—these agents achieve inadequate tissue concentrations outside the bladder 2, 8, 4
• Do NOT use amoxicillin or ampicillin alone due to resistance rates exceeding 30% globally 2
• Do NOT use tigecycline for any UTI—it achieves insufficient urinary concentrations and is strongly contraindicated 1, 4
• Avoid empiric trimethoprim-sulfamethoxazole without susceptibility data in areas with high resistance rates or in patients with recent fluoroquinolone exposure 3
• Do NOT treat asymptomatic bacteriuria except in pregnancy or before invasive urologic procedures with expected mucosal bleeding 1

Step-Down and Monitoring Strategy

• Transition to oral therapy when patient is hemodynamically stable, afebrile for ≥48 hours, and able to tolerate oral medications 2
• Reassess clinical response within 72 hours; if symptoms persist, obtain imaging (CT or ultrasound) to exclude abscess or obstruction 2
• Replace indwelling catheters that have been in place ≥2 weeks at onset of CAUTI to hasten symptom resolution 2
• Obtain urine culture before initiating therapy to guide definitive treatment, especially given rising resistance patterns 2, 8

Specific Dosing Recommendations

• Ciprofloxacin: 500 mg PO twice daily for 7 days (uncomplicated pyelonephritis) or 250 mg PO twice daily for complicated UTI 7, 9
• Levofloxacin: 750 mg PO/IV once daily for 5 days (pyelonephritis) or 500 mg once daily for 7-10 days (complicated UTI) 5, 10, 11
• Trimethoprim-sulfamethoxazole: 160/800 mg twice daily for 14 days when used for pyelonephritis 2
• Gentamicin: 5 mg/kg IV daily for short-duration therapy (≤7 days) to minimize nephrotoxicity 4, 6