What is the recommended empiric intravenous antibiotic regimen and dosing for an adult with suspected acute pyelonephritis presenting to the emergency department, including hydration and criteria for switching to oral therapy?

Emergency Management of Acute Pyelonephritis

For adults presenting to the emergency department with suspected acute pyelonephritis, initiate empiric intravenous therapy with ciprofloxacin 400 mg IV twice daily, levofloxacin 750 mg IV once daily, ceftriaxone 1-2 g IV once daily, or an aminoglycoside (gentamicin 5 mg/kg IV once daily) based on local resistance patterns, with aggressive IV hydration and admission criteria based on severity markers. 1, 2

Initial Risk Stratification in the ED

Immediately classify the patient as uncomplicated versus complicated pyelonephritis, as this determines the entire treatment pathway 2:

Uncomplicated pyelonephritis requires:

• No structural/functional urinary tract abnormalities
• No immunosuppression, pregnancy, or diabetes
• No signs of sepsis or hemodynamic instability 2

Complicated pyelonephritis includes any of the above risk factors, frank hematuria, or suspected obstruction 1, 2

Diagnostic Workup Before Antibiotics

• Obtain urine culture with antimicrobial susceptibility testing in all patients before initiating antibiotics 1, 2
• Blood cultures are reserved for patients with uncertain diagnosis, immunocompromised status, or suspected hematogenous infection 3
• Urinalysis with leukocyte esterase and nitrite testing has 75-84% sensitivity when either test is positive 3

Empiric IV Antibiotic Regimens and Dosing

First-Line IV Options for Hospitalized Patients:

Fluoroquinolones:

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

Extended-Spectrum Cephalosporins:

• Ceftriaxone 1-2 g IV once daily 1
• Cefotaxime 2 g IV three times daily 1

Extended-Spectrum Penicillins:

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

Aminoglycosides (with or without ampicillin):

• Gentamicin 5 mg/kg IV once daily 1
• Amikacin 15 mg/kg IV once daily 1

Critical Caveat on Fluoroquinolone Use:

If local fluoroquinolone resistance exceeds 10%, give an initial IV dose of ceftriaxone 1 g or gentamicin before considering oral fluoroquinolone therapy 1, 4

Admission Criteria from the ED

Hospitalize patients with:

• Complicated infections (obstruction, abscess, structural abnormalities)
• Sepsis or hemodynamic instability
• Persistent vomiting preventing oral intake
• Failed outpatient treatment
• Extremes of age
• Pregnancy
• Diabetes or chronic kidney disease
• Frank hematuria 1, 2, 3, 5

Hydration Protocol

Provide aggressive IV hydration as supportive therapy for all hospitalized patients with pyelonephritis 5

Criteria for Switching to Oral Therapy

Switch from IV to oral antibiotics when:

• Patient is afebrile for 24-48 hours
• Clinical improvement is evident (reduced flank pain, improved hemodynamics)
• Able to tolerate oral intake without vomiting
• Culture results available to guide targeted therapy 2, 5

Oral Step-Down Options:

• Ciprofloxacin 500-750 mg PO twice daily for 7 days 2
• Levofloxacin 750 mg PO once daily for 5 days 2
• Cefpodoxime 200 mg PO twice daily for 10 days 2
• Trimethoprim-sulfamethoxazole for 14 days (only if susceptible) 1, 2

Treatment Duration

• Fluoroquinolones: 5-7 days total 2
• Trimethoprim-sulfamethoxazole: 14 days 2
• Oral cephalosporins: 10 days 2
• Standard duration for most regimens: 7-14 days 2, 3

Urgent Imaging Indications from the ED

Perform urgent upper urinary tract imaging (CT with contrast preferred) for 1, 2:

• Frank hematuria present
• Suspected obstruction or abscess
• Immediate clinical deterioration
• Sepsis or hemodynamic instability
• Immunocompromised patients

Antimicrobial Resistance Considerations

• Tailor therapy based on culture and susceptibility results as soon as available 1
• Reserve carbapenems for multidrug-resistant organisms 1
• Avoid oral beta-lactams and trimethoprim-sulfamethoxazole as empiric therapy due to high resistance rates unless susceptibility is confirmed 4
• Local resistance patterns should guide all empiric therapy selection 1, 4

Follow-Up After ED Discharge

For patients discharged from the ED on oral therapy, repeat urine culture 1-2 weeks after completion of antibiotics 3