Cephalexin Coverage for Staphylococcus lugdunensis
Cephalexin provides effective coverage against Staphylococcus lugdunensis, as first-generation cephalosporins demonstrate good activity against staphylococci and streptococci, and S. lugdunensis is typically methicillin-susceptible.
Rationale for Coverage
First-generation cephalosporins like cephalexin are specifically noted for their excellent activity against staphylococcal species. 1 The Clinical Infectious Diseases guidelines explicitly state that first-generation cephalosporins have "good activity against staphylococci and streptococci." 1
S. lugdunensis, when methicillin-susceptible, behaves similarly to methicillin-susceptible Staphylococcus aureus (MSSA) in terms of antibiotic susceptibility patterns. 2, 3 First-generation cephalosporins are most active against gram-positive bacteria, particularly staphylococcal species. 2
Clinical Application
The WHO Essential Medicines guidelines (2024) list cefalexin as a first-choice agent for mild skin and soft tissue infections, which are commonly caused by staphylococcal species. 1 This recommendation was upgraded from second-choice to first-choice status in 2021, reflecting strong confidence in its efficacy against staphylococci. 1
Dosing Recommendations
For staphylococcal infections:
- Oral cephalexin: 500 mg three to four times daily 1
- Pediatric dosing: 50-100 mg/kg/day divided into multiple doses 4
Important Caveats
This recommendation applies ONLY to methicillin-susceptible S. lugdunensis. If methicillin resistance is suspected or confirmed, cephalexin will be ineffective, and alternative agents (vancomycin, linezolid, or daptomycin) must be used. 1, 5
When to Consider Alternatives
- If the patient has risk factors for MRSA (recent hospitalization, healthcare exposure, injection drug use, prior MRSA infection), empiric therapy should cover resistant organisms until susceptibilities are known. 1
- For severe or invasive S. lugdunensis infections (endocarditis, bacteremia, deep tissue infections), intravenous therapy with cefazolin or an anti-staphylococcal penicillin is preferred over oral cephalexin. 1
Comparative Efficacy
Cephalexin demonstrates cure rates of 90% or higher for staphylococcal skin infections, comparable to other anti-staphylococcal agents including dicloxacillin, cloxacillin, and clindamycin. 6 While cephalexin MICs for MSSA (and by extension, methicillin-susceptible S. lugdunensis) are typically 2-4 μg/mL—higher than parenteral agents like cefazolin or oxacillin—these concentrations are well within achievable therapeutic ranges with standard dosing. 7
Clinical Pearls
- Cephalexin's twice-daily dosing option enhances medication compliance compared to agents requiring more frequent administration. 6
- The suspension formulation is well-tolerated in pediatric patients. 6
- Side effects are generally mild and infrequent, primarily consisting of gastrointestinal upset and occasional rash. 6, 4