What is the best antibiotic for a patient with a recurrent urinary tract infection (UTI) due to Klebsiella pneumoniae, previously treated with Bactrim (trimethoprim/sulfamethoxazole) and now sensitive to Bactrim, ciprofloxacin, cephalosporins, and gentamicin, without signs of complicated UTI or sepsis?

From the Guidelines

For this patient with a recurrent UTI due to Klebsiella pneumoniae, I recommend ciprofloxacin 500 mg orally twice daily for 7 days. This recommendation is based on the most recent and highest quality study available, which suggests that ciprofloxacin is an effective treatment for uncomplicated UTIs, especially when the organism is susceptible to it 1. Although the patient was previously treated with Bactrim DS, which the organism is also sensitive to, the fact that the symptoms did not completely resolve suggests that a different antibiotic class may be necessary. Ciprofloxacin has good urinary penetration and is effective against Klebsiella pneumoniae, making it a suitable choice for this patient.

The patient's lack of flank pain and negative urinalysis for crystals, along with the absence of signs of complicated UTI or sepsis, support the use of oral therapy for an uncomplicated lower UTI. It is essential for the patient to complete the entire course of antibiotics, even if symptoms improve before completion, and to increase fluid intake to help flush the urinary system. A follow-up visit and urine culture after completion of therapy may be warranted due to the recurrent nature of the infection. The mechanism of action of ciprofloxacin, which involves inhibiting bacterial DNA gyrase and preventing DNA replication, makes it particularly effective against gram-negative organisms like Klebsiella pneumoniae 1.

Key considerations in this case include:

• The patient's previous treatment with Bactrim DS did not lead to complete resolution of symptoms
• The organism's susceptibility to ciprofloxacin, as well as other antibiotics like Bactrim, cefalosporins, and gentamicin
• The absence of signs of complicated UTI or sepsis, which allows for oral therapy
• The importance of completing the full course of antibiotics and follow-up to ensure eradication of the infection and prevent recurrence.

From the FDA Drug Label

Ciprofloxacin Tablets USP, 250 mg, 500 mg and 750 mg is indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the conditions and patient populations listed below. Adult Patients: Urinary Tract Infections caused by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Proteus mirabilis, Providencia rettgeri, Morganella morganii, Citrobacter diversus, Citrobacter freundii, Pseudomonas aeruginosa, methicillin-susceptible Staphylococcus epidermidis, Staphylococcus saprophyticus, or Enterococcus faecalis

The best antibiotic to give is ciprofloxacin because the patient's recent culture is positive for Klebsiella pneumoniae and sensitive to ciprofloxacin, and the patient has an uncomplicated urinary tract infection with no signs of sepsis 2.

• The patient's previous treatment with Bactrim did not completely resolve the symptoms, and the current infection is still sensitive to Bactrim, but ciprofloxacin is a suitable alternative.
• Gentamicin is typically reserved for more severe or complicated infections, and its use may be associated with more toxicity 3.
• Cefixime is also an option, but its effectiveness against Klebsiella pneumoniae is not as well-established as ciprofloxacin 4.

From the Research

Treatment Options for Klebsiella pneumoniae UTI

The patient has a history of UTI caused by Klebsiella pneumoniae, which was previously treated with Bactrim (trimethoprim-sulfamethoxazole) double strength for 3 days. The recent culture is again positive for Klebsiella pneumoniae, and the isolate is sensitive to Bactrim, ciprofloxacin, cephalosporins, and gentamicin.

• The patient's symptoms did not completely resolve after the previous treatment, suggesting that a longer treatment course may be necessary.
• Studies have shown that trimethoprim-sulfamethoxazole (TMP-SMZ) can be an effective treatment option for Klebsiella pneumoniae infections, including those caused by multidrug-resistant strains 5, 6, 7, 8.
• A study published in 2025 found that a structured, long-term TMP-SMZ regimen was effective in eradicating multidrug-resistant K. pneumoniae UTIs in 11 patients who had failed at least two prior antibiotic treatments 8.
• Another study published in 2017 reported that TMP-SMZ was effective in treating carbapenemase-producing K. pneumoniae infections, with a cure rate of 71.4% 5.
• The use of TMP-SMZ in combination with other antibiotics, such as colistin, may also be effective against carbapenem-resistant K. pneumoniae isolates 6.

Antibiotic Selection

Based on the available evidence, Bactrim (trimethoprim-sulfamethoxazole) may be a suitable treatment option for this patient, given its sensitivity to the antibiotic and the patient's previous treatment history.

• However, the treatment course should be longer than the previous 3-day course to ensure complete eradication of the infection.
• The patient's renal function and urine output should be closely monitored during treatment to ensure that the antibiotic is effective and not causing any adverse effects.
• Other treatment options, such as ciprofloxacin, cephalosporins, and gentamicin, may also be considered based on the patient's clinical condition and the results of the urine culture and sensitivity testing.