Keflex (Cephalexin) for MSSA Urinary Tract Infections
Yes, Keflex (cephalexin) is an effective treatment option for methicillin-susceptible Staphylococcus aureus (MSSA) urinary tract infections (UTIs). 1, 2
Rationale for Using Cephalexin for MSSA UTIs
- Cephalexin is a first-generation cephalosporin with excellent activity against MSSA and achieves high concentrations in the urine, where it maintains full activity against common UTI pathogens 2
- For MSSA infections, cephalexin is specifically listed as an appropriate oral treatment option in multiple guidelines 1
- Cephalexin has been repeatedly documented as clinically effective in urinary tract infections in numerous studies since the 1970s 2
Dosing Recommendations
- For adults with uncomplicated UTIs, cephalexin can be administered as:
- For children, weight-based dosing of 25-50 mg/kg/day divided into 3-4 doses is recommended 1
Advantages of Cephalexin for MSSA UTIs
- Excellent bioavailability and urinary penetration 2, 4
- Favorable safety profile compared to some alternatives 1
- Can be used as a fluoroquinolone-sparing alternative, which is important for antimicrobial stewardship 4
- More convenient than nafcillin with less bone marrow suppression 1
Clinical Considerations
- Cephalexin is appropriate for patients with penicillin allergies except those with immediate hypersensitivity reactions 1
- For patients with severe infections or systemic symptoms, initial IV therapy with cefazolin may be preferred before transitioning to oral cephalexin 1
- Recent studies support the efficacy of cephalexin against MSSA, with MIC50 values of 2 μg/mL and MIC90 values of 4 μg/mL, which are within achievable urinary concentrations 5
Potential Limitations and Alternatives
- For complicated infections or patients with severe symptoms, parenteral therapy may be initially required 1
- In cases of brain abscess resulting from MSSA infection, nafcillin is preferred over cefazolin due to better blood-brain barrier penetration 1
- For patients with true immediate-type hypersensitivity to β-lactams, alternative agents such as trimethoprim-sulfamethoxazole or clindamycin may be considered 1
Practical Approach
- Confirm MSSA as the causative pathogen through urine culture 1
- For uncomplicated UTIs in adults, prescribe cephalexin 500 mg twice daily for 5-7 days 3, 4
- For more severe infections, consider initial parenteral therapy with cefazolin before transitioning to oral cephalexin 1
- Monitor for clinical response within 48-72 hours 3
- If symptoms persist or worsen, reevaluate for complications or resistance 3
Cephalexin remains a reliable, effective, and well-tolerated option for treating MSSA UTIs with the added benefits of good oral bioavailability and established safety profile.