Is Keflex (Cephalexin) an appropriate treatment for a dog scratch in an elderly patient with multiple comorbidities?

Keflex (Cephalexin) Is Not Appropriate for Dog Scratch Infections in Elderly Patients with Comorbidities

Cephalexin should not be used for dog scratch infections in elderly patients with comorbidities as it has poor in vitro activity against Pasteurella multocida, a common pathogen in animal bite and scratch wounds. 1

Microbiology of Dog-Related Wounds

Dog scratches and bites have a complex polymicrobial profile that requires specific antibiotic coverage:

• Pasteurella species are isolated from approximately 50% of dog-related wounds 1
• Staphylococci and streptococci are found in about 40% of animal bite wounds 1
• Anaerobic bacteria are present in 50% of dog-related wounds 1
• Capnocytophaga canimorsus, a gram-negative rod, can cause serious infections especially in elderly or immunocompromised patients 1

Appropriate Antibiotic Selection

For elderly patients with multiple comorbidities who have sustained a dog scratch, the following antibiotics are recommended:

First-line therapy:

• Amoxicillin-clavulanate (recommended with B-II level evidence) 1
  • Provides coverage against both Pasteurella and common skin flora
  • Studied specifically in animal bite wounds

Alternative oral options:

• Doxycycline
• Penicillin VK plus dicloxacillin
• Fluoroquinolones (ciprofloxacin, levofloxacin) plus metronidazole for anaerobic coverage 1

Intravenous options (for severe infections):

• Beta-lactam/beta-lactamase combinations (ampicillin-sulbactam)
• Piperacillin-tazobactam
• Second-generation cephalosporins (cefoxitin)
• Carbapenems (ertapenem, imipenem, meropenem) 1

Why Cephalexin Should Be Avoided

First-generation cephalosporins like cephalexin have specific limitations in this context:

• Poor in vitro activity against Pasteurella multocida (D-III level evidence) 1
• Inadequate coverage of the polymicrobial nature of dog-related wounds
• Risk of treatment failure in elderly patients with comorbidities who are already at higher risk for complications 2

Special Considerations for Elderly Patients

Elderly patients with comorbidities require particular attention:

• Higher risk of systemic complications from localized infections
• Potential for impaired renal function affecting drug clearance 2
• Increased risk of drug interactions with multiple medications
• Cephalexin should be administered with caution in patients with markedly impaired renal function 2

Wound Management

In addition to appropriate antibiotic selection, proper wound management is crucial:

• Thorough cleansing with sterile normal saline
• Removal of superficial debris
• Elevation of the injured body part to reduce swelling
• Close follow-up within 24 hours for elderly patients 1

Potential Complications

Failure to provide appropriate antibiotic coverage can lead to:

• Progression of cellulitis
• Septic arthritis or osteomyelitis (especially with wounds near joints)
• Tendonitis
• Bacteremia (rare but serious, especially in elderly patients) 1
• Severe and progressive infections, as documented in case reports of dog scratch infections 3

Treatment Duration

Standard treatment duration for uncomplicated infections is 5-6 days 4, but may need extension if:

• The infection has not adequately improved
• The patient is immunocompromised
• There are deep space infections 4

In conclusion, while cephalexin is an effective antibiotic for many skin and soft tissue infections caused by streptococci and staphylococci 5, it is not appropriate for dog scratch wounds in elderly patients with comorbidities due to its inadequate coverage of Pasteurella multocida and the polymicrobial nature of these wounds.