What antibiotics are used to treat a kidney infection?

Antibiotic Treatment for Kidney Infection (Pyelonephritis)

For uncomplicated pyelonephritis, fluoroquinolones are the preferred first-line agents: levofloxacin 750 mg once daily for 5 days or ciprofloxacin 500-750 mg twice daily for 7 days, with trimethoprim-sulfamethoxazole 160/800 mg twice daily for 14 days reserved as an alternative when susceptibility is confirmed. 1

Outpatient Oral Treatment Algorithm

First-Line Options (Fluoroquinolones)

• Levofloxacin 750 mg once daily for 5 days is the optimal choice, offering once-daily dosing with proven efficacy and clinical cure rates exceeding 93% 1
• Ciprofloxacin 500-750 mg twice daily for 7 days is equally effective with similar cure rates, though requires twice-daily administration 1
• Fluoroquinolones should only be used when local resistance rates are <10% 1

Second-Line Option (When Susceptibility Known)

• Trimethoprim-sulfamethoxazole (TMP-SMX) 160/800 mg twice daily for 14 days can be used when culture and susceptibility testing confirm organism susceptibility 1
• TMP-SMX should never be used empirically without culture results due to high resistance rates (up to 55% in E. coli) and corresponding treatment failure 1, 2
• Clinical cure rates with TMP-SMX reach 92% when organisms are susceptible, but require longer treatment duration (14 days vs 5-7 days for fluoroquinolones) 1

Oral Cephalosporins (Limited Role)

• Cefpodoxime 200 mg twice daily for 10 days or ceftibuten 400 mg once daily for 10 days may be considered 1
• Oral cephalosporins achieve significantly lower blood and urinary concentrations than IV formulations and have inferior efficacy compared to fluoroquinolones 1
• An initial IV dose of ceftriaxone 1g should be administered before transitioning to oral cephalosporins 1, 3

Inpatient IV Treatment Algorithm

Initial Empiric IV Therapy

• Fluoroquinolones: Ciprofloxacin 400 mg IV twice daily or levofloxacin 750 mg IV once daily 1
• Extended-spectrum cephalosporins: Ceftriaxone 1-2 g IV once daily or cefepime 1-2 g IV twice daily 1
• Aminoglycosides: Gentamicin 5 mg/kg IV once daily or amikacin 15 mg/kg IV once daily (with or without ampicillin) 1, 4
• Extended-spectrum penicillins: Piperacillin-tazobactam 2.5-4.5 g IV three times daily 1

Carbapenems and Novel Agents (Reserved for Resistant Organisms)

• Only consider imipenem-cilastatin, meropenem, ceftolozane-tazobactam, ceftazidime-avibactam, or meropenem-vaborbactam when early culture results indicate multidrug-resistant organisms 1
• These broad-spectrum agents should be reserved to preserve their efficacy against resistant pathogens 1

Critical Pitfalls and Caveats

Antibiotics to Avoid

• Nitrofurantoin, fosfomycin, and pivmecillinam should never be used for pyelonephritis due to insufficient data regarding efficacy and inadequate tissue penetration 1
• Amoxicillin and ampicillin should not be used empirically due to resistance rates exceeding 40% in E. coli 3, 2
• Oral β-lactams (including cephalexin) have inferior efficacy compared to first-line agents and should only be used when other options cannot be used 1, 5

Fluoroquinolone Considerations

• While highly effective, fluoroquinolones carry risks of serious adverse effects including tendon rupture, peripheral neuropathy, and CNS effects 1
• Rare cases of fluoroquinolone-induced renal failure have been reported, though causality is difficult to establish 6
• Despite these concerns, the benefit-to-risk ratio favors fluoroquinolones as first-line therapy for pyelonephritis given their superior efficacy 1

Essential Diagnostic Steps

• Always obtain urine culture and susceptibility testing before initiating antibiotics to guide targeted therapy 1, 3
• Perform ultrasound imaging to rule out urinary tract obstruction in patients with history of urolithiasis, renal dysfunction, or high urine pH 1
• If fever persists after 72 hours of appropriate therapy, obtain contrast-enhanced CT scan to evaluate for complications such as abscess formation 1

Treatment Duration Evidence

• Three recent RCTs demonstrated that 5-day fluoroquinolone courses are noninferior to 10-day courses, with clinical cure rates upward of 93% 1
• Shorter courses are associated with slightly higher recurrence rates within 4-6 weeks but reduce antibiotic exposure and resistance development 1
• The 14-day duration for TMP-SMX reflects its lower tissue penetration compared to fluoroquinolones 1

Resistance Patterns

• E. coli accounts for >75% of pyelonephritis cases and demonstrates high resistance to ciprofloxacin (48%), cotrimoxazole (55%), and ceftriaxone (34%) in some regions 1, 2
• Local resistance patterns should guide empiric therapy selection, with fluoroquinolones reserved for areas where resistance remains <10% 1
• Klebsiella pneumoniae isolates may show universal resistance to ciprofloxacin in certain populations 2