Does Keflex Cover Streptococcus?
Yes, Keflex (cephalexin) is effective against most streptococcal species and is specifically approved by the FDA for infections caused by Streptococcus pneumoniae and Streptococcus pyogenes (Group A Streptococcus). 1
FDA-Approved Streptococcal Coverage
Cephalexin has documented activity against the following streptococcal species:
- Streptococcus pneumoniae (penicillin-susceptible strains) 1
- Streptococcus pyogenes (Group A Streptococcus) 1
The FDA label explicitly states that cephalexin is indicated for respiratory tract infections, otitis media, and skin/soft tissue infections caused by these organisms. 1
Clinical Applications for Streptococcal Infections
Group A Streptococcal Pharyngitis
Cephalexin is recommended as a second-choice antibiotic for Group A streptococcal pharyngitis, particularly in penicillin-allergic patients. 2
- The IDSA guidelines recommend cephalexin (20 mg/kg per dose twice daily, maximum 500 mg per dose) for 10 days in patients with penicillin allergy. 2
- The WHO Working Group selected cephalexin as a second-line option based on lower relapse rates, good tolerability, and narrow spectrum compared to macrolides. 2
- Clinical studies demonstrate that cephalexin is comparable to penicillin in treating streptococcal pharyngitis, with cure rates exceeding 90%. 3, 4
Important caveat: Avoid cephalexin in patients with a history of anaphylaxis, angioedema, or urticaria to penicillins due to potential cross-reactivity. 2
Skin and Soft Tissue Infections
For streptococcal skin infections, cephalexin achieves cure rates of 90% or higher. 5
- The WHO recognizes cephalexin as a first-choice treatment for mild skin and soft tissue infections caused by streptococci. 6
- Cephalexin is effective for impetigo, cellulitis, and other streptococcal skin infections at standard dosing (500 mg every 6 hours in adults). 6, 5
- Clinical trials show cephalexin is comparable to erythromycin, clindamycin, and dicloxacillin for streptococcal and staphylococcal skin infections. 5, 7
Respiratory Tract Infections
Cephalexin is FDA-approved for respiratory tract infections caused by S. pneumoniae and S. pyogenes, though penicillin remains the preferred agent when streptococcal infection is confirmed. 1, 3
Critical Limitations
Does NOT Cover:
- Penicillin-resistant Streptococcus pneumoniae: These strains are usually cross-resistant to beta-lactam antibiotics including cephalexin. 1
- Enterococcus species: Methicillin-resistant staphylococci and most enterococci (including Enterococcus faecalis) are resistant to all cephalosporins. 1
- Group A Streptococcus in cellulitis when used with Bactrim: When cellulitis may involve Group A Streptococcus, Bactrim should not be used alone due to intrinsic resistance; cephalexin or another beta-lactam must be added. 8
Dosing Recommendations
Standard adult dosing: 250-500 mg four times daily OR 500 mg twice daily for 10 days. 2, 9
Pediatric dosing: 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days. 2
- Twice-daily dosing is equally effective as four-times-daily administration and improves compliance. 4, 9
- For skin infections, 5-day courses may be sufficient if clinical improvement is observed, though 10 days remains standard for pharyngitis. 6
Practical Considerations
- Bioavailability: Cephalexin is acid-stable and well-absorbed orally, achieving peak serum levels of approximately 18 mcg/mL after a 500 mg dose. 1
- Excretion: Over 90% is excreted unchanged in urine within 8 hours, making it effective for urinary tract infections as well. 1
- Side effects: Generally mild, consisting primarily of gastrointestinal upset, rash, and urticaria in fewer than 5% of patients. 3, 5
- Cost-effectiveness: Generic cephalexin is widely available and relatively inexpensive compared to newer agents. 2