Is cefalexin (a first-generation cephalosporin) an appropriate treatment option for a patient with varicella and a secondary bacterial infection, such as Staphylococcus aureus or Group A Streptococcus?

Cefalexin for Varicella with Secondary Bacterial Infection

Cefalexin is an appropriate and effective treatment option for secondary bacterial skin infections complicating varicella, particularly when caused by methicillin-susceptible Staphylococcus aureus (MSSA) or Group A Streptococcus. 1, 2

Primary Recommendation

For varicella-associated secondary bacterial skin infections, cefalexin should be prescribed at 500 mg orally four times daily in adults (or 25-50 mg/kg/day divided into 3-4 doses in children, maximum 500 mg per dose) for 7-10 days. 1, 3, 2

Evidence Supporting Cefalexin Use

Guideline-Based Recommendations

• The Infectious Diseases Society of America (IDSA) explicitly recommends cefalexin for impetigo and skin/soft tissue infections caused by S. aureus and Streptococcus species, which are the primary pathogens in varicella-associated secondary bacterial infections. 1

• The FDA label indicates cefalexin is approved for skin and skin structure infections caused by S. aureus and/or Streptococcus pyogenes, making it directly applicable to this clinical scenario. 2

• Necrotizing fasciitis arising after varicella is usually due to S. pyogenes or community-acquired MRSA, and cefalexin covers the former pathogen effectively. 1

Clinical Context for Varicella

• Secondary bacterial infections complicating varicella typically occur when skin lesions become superinfected with S. aureus or Group A Streptococcus. 1

• Without adequate treatment, immunocompromised patients with varicella may develop chronic ulcerations with persistent viral replication complicated by secondary bacterial and fungal superinfections. 1

Dosing Specifications

Adult Dosing

• Standard regimen: 250-500 mg orally four times daily for 10 days 4, 3
• Alternative twice-daily dosing: 500 mg orally twice daily for 10 days (enhances compliance) 4, 5

Pediatric Dosing

• 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days 4
• Alternative: 25-50 mg/kg/day divided into 3-4 doses 3, 2

Critical Contraindications and Warnings

Penicillin Allergy Considerations

Patients with immediate-type penicillin reactions (anaphylaxis, angioedema, or urticaria) should NOT receive cefalexin due to up to 10% cross-reactivity risk. 4

• For these patients, alternative agents include clindamycin or azithromycin. 4, 6

• Patients with non-immediate penicillin allergies (e.g., delayed rash) can generally receive cefalexin safely. 4

MRSA Limitations

Cefalexin has NO activity against methicillin-resistant S. aureus (MRSA). 3, 2

• If community-acquired MRSA is suspected (purulent infections, treatment failure, or high local prevalence), alternative agents are required. 1, 3

• Appropriate MRSA-active alternatives include clindamycin (300-450 mg orally 3-4 times daily), doxycycline (100 mg twice daily), or trimethoprim-sulfamethoxazole. 1, 6

When to Escalate Therapy

Signs Requiring Broader Coverage

If the patient develops necrotizing fasciitis or severe systemic toxicity, immediate escalation to combination parenteral therapy is mandatory. 1

• Recommended regimen: Penicillin plus clindamycin for documented Group A streptococcal necrotizing fasciitis. 1

• Alternative: Vancomycin or linezolid plus piperacillin-tazobactam (or a carbapenem, or ceftriaxone and metronidazole) for polymicrobial or uncertain etiology. 1

Treatment Failure Indicators

• Worsening symptoms after 48-72 hours of cefalexin therapy suggests either MRSA infection or inadequate source control. 1

• Recrudescent fever or increasing dyspnea warrants reassessment and possible antibiotic change. 1

Practical Advantages of Cefalexin

• High cure rates (90% or higher) for streptococcal and staphylococcal skin infections have been maintained over decades of use. 5

• Excellent oral bioavailability with rapid absorption in the upper intestine, achieving urinary concentrations of 500-1000 mcg/mL following 250-500 mg doses. 7

• Does not disturb lower bowel flora due to absorption high in the intestinal tract. 7

• Low incidence of allergic reactions and gastrointestinal side effects. 7, 5

• Cost-effective with widely available generic formulations. 4

Common Pitfalls to Avoid

• Do not use cefalexin monotherapy for purulent cellulitis or abscesses, as these are frequently caused by community-acquired MRSA. 3

• Do not prescribe cefalexin to patients with documented immediate-type penicillin allergies without confirming allergy history. 4

• Ensure 10-day treatment duration for streptococcal infections to prevent rheumatic fever, even though cefalexin data for rheumatic fever prevention are limited. 2

• Reduce dosage proportionally in patients with creatinine clearance <30 mL/min. 7