Management Change When Flank Pain Develops
If a woman initially treated for uncomplicated cystitis develops flank pain, you must immediately reclassify this as acute pyelonephritis and change to pyelonephritis-appropriate antibiotics with longer duration therapy. 1
Immediate Diagnostic Steps
Obtain a urine culture with antimicrobial susceptibility testing before starting new antibiotics to guide therapy if the patient fails to respond to initial empiric treatment. 2, 3, 4
Key Clinical Features to Assess
- Fever ≥38°C is present in most cases, though may be absent in up to 20% of patients, particularly elderly, diabetic, or immunocompromised individuals 2, 3
- Flank pain or costovertebral angle tenderness is nearly universal in pyelonephritis and its absence should raise suspicion of an alternative diagnosis 2, 5
- Systemic symptoms including nausea, vomiting, chills, and malaise are common 2, 3
Critical Treatment Changes Required
Avoid These Agents Used for Cystitis
Do NOT continue nitrofurantoin, fosfomycin, or pivmecillinam - these agents achieve insufficient tissue levels in the kidney and are explicitly contraindicated for pyelonephritis. 1, 4
Appropriate Antibiotic Selection
For outpatient management (if patient can tolerate oral intake and appears well):
Fluoroquinolones are first-line if local resistance is ≤10%: 4, 5
- Ciprofloxacin 500-750 mg twice daily for 7 days, OR
- Levofloxacin 750 mg once daily for 5 days
If fluoroquinolone resistance exceeds 10%: Give an initial IV dose of ceftriaxone 1 gram, then transition to oral fluoroquinolone 4
For hospitalization (severe illness, inability to tolerate oral intake, immunocompromise, diabetes, pregnancy):
- Ceftriaxone 1-2 grams IV once daily is the preferred initial agent 3
- Alternative inpatient regimens include fluoroquinolones, aminoglycosides, or other cephalosporins 5
Duration of Therapy
Treat for 7-14 days depending on agent used - this is substantially longer than the 3-5 day courses used for cystitis. 4, 6
- Fluoroquinolones or cephalosporins: 7-14 days
- Trimethoprim-sulfamethoxazole: 14 days (if susceptible) 4
Monitoring and Follow-Up
Reassess within 48-72 hours to ensure clinical improvement. 3, 4
- 95% of patients with uncomplicated pyelonephritis become afebrile within 48 hours of appropriate antibiotic therapy, and nearly 100% within 72 hours 3
Obtain contrast-enhanced CT of abdomen/pelvis if:
- Patient remains febrile after 72 hours of appropriate antibiotics 3, 4
- Clinical deterioration occurs 3
- Patient has diabetes or is immunocompromised (lower threshold for imaging) 2, 3
High-Risk Features Requiring Hospitalization
Consider inpatient management if any of the following are present: 3
- Diabetes mellitus
- Immunocompromise or transplant recipient
- Pregnancy
- Anatomic urinary tract abnormalities
- Indwelling catheter
- Inability to tolerate oral intake or medications
- Severe systemic illness
Common Pitfalls to Avoid
Do not obtain imaging initially in uncomplicated cases - CT, MRI, and ultrasound are not indicated for initial evaluation of uncomplicated pyelonephritis. 3
Do not use beta-lactam antibiotics empirically for outpatient treatment due to high resistance rates, unless susceptibility is confirmed. 5
Do not underestimate diabetic patients - up to 50% lack typical flank tenderness, making diagnosis more challenging, and they are at higher risk for complications including renal abscesses and emphysematous pyelonephritis. 2