Keflex Does Not Provide Reliable Coverage for Enterococcus UTI
Keflex (cephalexin) should not be used to treat Enterococcus urinary tract infections because first and second-generation cephalosporins lack reliable activity against Enterococcus species. 1
Why Cephalexin Fails Against Enterococcus
Enterococcus species are intrinsically resistant to cephalosporins, including first-generation agents like cephalexin, due to their low-affinity penicillin-binding proteins. 2
While cephalexin achieves high urinary concentrations and works well against typical uropathogens like E. coli, Proteus, and Klebsiella, it does not cover Enterococcus species that commonly cause complicated UTIs. 1, 3
Historical susceptibility testing from 1970 demonstrated that cephalothin and cephaloridine (first-generation cephalosporins) showed poor activity against Enterococcus, even when pH was optimized. 2
Appropriate Treatment Options for Enterococcal UTI
For Uncomplicated Lower UTI (Cystitis)
Fosfomycin 3g PO single dose is FDA-approved specifically for UTI caused by E. faecalis and represents an excellent oral option. 1, 4
Nitrofurantoin 100mg PO every 6 hours for 5-7 days has good in vitro activity against vancomycin-resistant Enterococcus (VRE) and is appropriate for lower UTI. 1, 4
Ampicillin 500mg PO/IV every 8 hours remains the drug of choice for ampicillin-susceptible Enterococcus infections. 1
For Complicated UTI or Pyelonephritis
Ampicillin 2g IV every 6 hours plus gentamicin is recommended as empirical treatment for complicated UTI with systemic symptoms when Enterococcus is suspected. 1, 4
High-dose ampicillin (18-30g IV daily) or amoxicillin (500mg every 8 hours) can overcome ampicillin resistance in urinary tract infections due to high urinary drug concentrations, with clinical cure rates of 88.1% even for ampicillin-resistant VRE. 1, 5
For Vancomycin-Resistant Enterococcus (VRE)
Linezolid 600mg IV/PO every 12 hours is effective for VRE infections, though it should be avoided for bacteremia due to its bacteriostatic nature. 1, 4
Daptomycin 8-12 mg/kg IV daily is preferred for serious VRE infections requiring bactericidal activity, but should not be used for UTI as monotherapy. 1
Critical Clinical Pitfalls
Do not treat asymptomatic bacteriuria with Enterococcus, as this fosters resistance without clinical benefit and represents colonization rather than true infection. 1, 4
Obtain urine culture with susceptibility testing before initiating therapy for Enterococcus UTI, as resistance patterns are unpredictable. 4
Remove indwelling urinary catheters immediately if present, as catheterization is a major risk factor for enterococcal UTI and may represent the primary source requiring control. 1, 4
Differentiate between E. faecalis and E. faecium, as E. faecium tends to have higher resistance rates and worse outcomes, particularly with VRE strains. 1
Treatment Duration
5-7 days for uncomplicated lower UTI (cystitis) is sufficient with appropriate agents like fosfomycin or nitrofurantoin. 4
7-14 days for complicated UTI, with 14 days recommended for men when prostatitis cannot be excluded. 1, 4
10-14 days for pyelonephritis or bloodstream infection to ensure adequate source control and prevent relapse. 4