From the Guidelines
Yes, it is appropriate to use cephalexin to treat this 64-year-old female patient with an E. coli UTI that is susceptible to cefepime and cefazolin. The typical regimen would be cephalexin 500 mg orally four times daily for 7 days for uncomplicated UTIs, or 10-14 days if the infection is complicated. Cephalexin is an oral first-generation cephalosporin that shares the same spectrum of activity as cefazolin (which is an IV first-generation cephalosporin). Since the E. coli is susceptible to cefazolin, it will also be susceptible to cephalexin, as noted in the guidelines for treating urinary tract infections 1. This is an example of "class susceptibility" where susceptibility to one agent in a class can predict susceptibility to another agent in the same class. Cephalexin provides good urinary tract penetration and is an appropriate step-down oral option when IV antibiotics are not needed, as supported by the evidence on antimicrobial agents for oral treatment of UTI 2. Some key points to consider when treating UTIs include:
- Ensuring the patient completes the full course of antibiotics even if symptoms improve before completion
- Advising the patient to increase fluid intake during treatment
- Following up for reassessment if symptoms worsen or do not improve within 48-72 hours
- Considering local antimicrobial susceptibility patterns, particularly for E. coli, as resistance rates can vary significantly by region 3
- Being aware that while cephalexin is a suitable option, other antimicrobials like nitrofurantoin, fosfomycin, and mecillinam may also be appropriate based on local resistance patterns and individual patient factors 1, 3.
From the FDA Drug Label
Genitourinary tract infections, including acute prostatitis, caused by Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae The patient has a UTI caused by E. coli, which is a susceptible strain according to the drug label.
- Key points:
- The drug label indicates cephalexin is effective against E. coli
- The patient's E. coli is susceptible to cefepime and cefazolin, but the label does support the use of cephalexin for E. coli UTIs. Therefore, it is appropriate to use cephalexin to treat this patient's UTI 4.
From the Research
Treatment of Urinary Tract Infections
- The patient has a urinary tract infection (UTI) caused by E. coli, which is susceptible to cefepime and cefazolin 5.
- Cephalexin is a second-line option for the treatment of UTIs, and its use is recommended when the pathogen is susceptible to it 5, 6.
- The efficacy of cephalexin in treating UTIs caused by E. coli has been demonstrated in several studies, with high cure rates and low resistance rates 7, 6.
- Cephalexin can be administered at a dose of 500 mg twice or thrice daily, making it a convenient option for patients 7, 6.
Antimicrobial Susceptibility Patterns
- E. coli isolates have shown varying susceptibility patterns to different antimicrobial agents, with high resistance rates to some agents such as ampicillin and ciprofloxacin 8, 9.
- Cefazolin and cefepime have been shown to be effective against E. coli, with low resistance rates 5, 9.
- The use of cephalexin as a treatment option for UTIs caused by E. coli is supported by its susceptibility pattern, with low resistance rates reported in several studies 7, 6.