What is the treatment for flank pain with foul-smelling urine and normal retroperitoneal ultrasound (US) findings?

From the Guidelines

The recommended treatment for flank pain with foul-smelling urine and normal retroperitoneal ultrasound is empiric antibiotic therapy with fluoroquinolones or cephalosporins for a presumed urinary tract infection (UTI) that may have ascended to the kidneys (pyelonephritis). According to the European Association of Urology guidelines on urological infections 1, fluoroquinolones and cephalosporins are the only antimicrobial agents that can be recommended for oral empiric treatment of uncomplicated pyelonephritis. Initial treatment should include an oral fluoroquinolone such as ciprofloxacin 500 mg twice daily for 7-14 days.

For diagnosis, urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis 1. In addition, a urine culture and antimicrobial susceptibility testing should be performed in all cases of pyelonephritis. Evaluation of the upper urinary tract via ultrasound has already been performed, which is in line with the guidelines to rule out urinary tract obstruction or renal stone disease 1.

Key considerations in management include:

• Adequate hydration is essential, along with analgesics such as acetaminophen or NSAIDs for pain relief.
• A urine culture should be obtained before starting antibiotics to guide therapy if the empiric regimen fails.
• The combination of flank pain and foul-smelling urine strongly suggests a kidney infection even with normal imaging, as early pyelonephritis may not show structural changes on ultrasound.
• Prompt treatment is necessary to prevent complications such as sepsis or abscess formation.
• If symptoms do not improve within 48-72 hours of appropriate antibiotic therapy, further evaluation with additional imaging studies like CT scan may be warranted to rule out complications or alternative diagnoses 1.

From the FDA Drug Label

To reduce the development of drug-resistant bacteria and maintain the effectiveness of sulfamethoxazole and trimethoprim oral suspension and other antibacterial drugs, sulfamethoxazole and trimethoprim oral suspension should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria Urinary Tract Infections For the treatment of urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis and Proteus vulgaris

The patient's symptoms of flank pain and foul smelling urine suggest a urinary tract infection. Given the patient has a normal retroperitoneal US, the treatment for a urinary tract infection with trimethoprim/sulfamethoxazole (PO) may be appropriate if the infection is caused by a susceptible strain of the listed organisms 2.

• Key considerations:
  • The patient's symptoms and test results should be evaluated to determine if the infection is caused by a susceptible strain.
  • The decision to use trimethoprim/sulfamethoxazole (PO) should be based on the presence of a proven or strongly suspected bacterial infection.
  • Local epidemiology and susceptibility patterns should be considered in selecting or modifying antibacterial therapy.

From the Research

Symptoms and Diagnosis

• Flank pain and foul-smelling urine are symptoms that may indicate a urinary tract infection (UTI) 3, 4, 5
• A normal retroperitoneal ultrasound (US) may not rule out a UTI, as the infection may be located in the upper or lower urinary tract 4, 5
• The diagnosis of UTI is usually made based on clinical presentation, and may involve urine culture and other diagnostic tests 3, 4, 5

Treatment Options

• Treatment of uncomplicated cystitis (bladder infection) usually involves short-course antimicrobial regimens 3
• Treatment of pyelonephritis (kidney infection) may involve longer courses of antimicrobial therapy, and may require hospitalization in severe cases 4, 6, 7
• Antimicrobial resistance is a growing concern in the treatment of UTIs, and may require alternative treatment options 3, 4, 6

Specific Treatment Regimens

• A 7-day course of ciprofloxacin may be effective for the treatment of acute uncomplicated pyelonephritis in women 6
• A 14-day course of trimethoprim-sulfamethoxazole may be less effective than ciprofloxacin for the treatment of acute uncomplicated pyelonephritis in women 6
• Extended-release ciprofloxacin (1,000 mg once daily) may be as effective as conventional ciprofloxacin (500 mg twice daily) for the treatment of complicated urinary tract infections and acute uncomplicated pyelonephritis 7