Cephalexin Coverage for UTIs
Cephalexin is effective against most common UTI pathogens including E. coli, Klebsiella pneumoniae, and Proteus mirabilis, making it a suitable alternative treatment option for uncomplicated urinary tract infections. 1, 2
Antimicrobial Spectrum
Cephalexin demonstrates activity against the following UTI pathogens:
Gram-positive organisms:
- Staphylococcus aureus (including penicillinase-producing strains)
- Streptococcus pneumoniae (penicillin-susceptible strains)
- Streptococcus pyogenes
Gram-negative organisms:
- Escherichia coli (most common UTI pathogen)
- Klebsiella pneumoniae
- Proteus mirabilis
- Haemophilus influenzae
- Moraxella catarrhalis 1
Important Limitations
Cephalexin has notable coverage gaps that clinicians should be aware of:
- Not effective against:
- Methicillin-resistant Staphylococcus aureus (MRSA)
- Most Enterococcus species (including E. faecalis)
- Most Enterobacter species
- Morganella morganii
- Proteus vulgaris
- Pseudomonas aeruginosa
- Acinetobacter species 1
Clinical Efficacy for UTIs
Recent evidence supports cephalexin's efficacy in treating uncomplicated UTIs:
- A 2023 retrospective study demonstrated 81.1% clinical success rate with cephalexin for empiric treatment of uncomplicated UTIs 2
- Another 2023 study showed no significant difference in treatment failure between twice-daily (12.7%) and four-times-daily (17%) dosing regimens 3
Dosing Considerations
- Standard dosing: 500 mg twice daily for 5-7 days for uncomplicated UTIs 3
- Twice-daily dosing is as effective as four-times-daily dosing, which may improve patient adherence 3
- Achieves high urinary concentrations (approximately 1000-5000 mcg/mL) following oral administration 1
Position in Treatment Guidelines
While the Infectious Diseases Society of America (IDSA) guidelines traditionally recommend non-β-lactam antibiotics as first-line agents for uncomplicated UTIs, cephalexin may be considered in certain situations:
- When first-line agents (nitrofurantoin, trimethoprim-sulfamethoxazole, fosfomycin) cannot be used 4
- In areas with increasing resistance to first-line agents 2
- As a fluoroquinolone-sparing alternative 5
Clinical Pearls
- Cephalexin is acid-stable and can be given without regard to meals 1
- Over 90% of the drug is excreted unchanged in the urine within 8 hours, contributing to high urinary concentrations 1
- Low-dose cephalexin (250 mg nightly) has been shown effective for prophylaxis of recurrent UTIs with minimal development of resistance 6
Potential Pitfalls
- Always consider local antibiogram data before empiric use, as resistance patterns vary geographically
- Not appropriate for complicated UTIs where resistant organisms or structural abnormalities are suspected
- Ineffective against ESBL-producing organisms, which are increasingly common in some regions 5
- Should not be used empirically when Enterococcus or Pseudomonas are suspected pathogens 1
Cephalexin remains a valuable option in the UTI treatment armamentarium, particularly as a fluoroquinolone-sparing alternative when first-line agents cannot be used or in regions with high resistance to traditional first-line therapies.