What is the recommended IV antibiotic regimen for an 89-year-old male with suspected cellulitis due to a dog scratch?

IV Antibiotic Therapy for Cellulitis Due to Dog Scratch

For an 89-year-old male with suspected cellulitis due to a dog scratch on his lower extremity, ampicillin-sulbactam (1.5-3.0 g IV every 6-8 hours) is the recommended first-line IV antibiotic therapy. 1

Rationale for Treatment Selection

Microbiology of Animal Bite Infections

• Dog bite/scratch infections are typically polymicrobial
• Pasteurella multocida is the predominant pathogen (especially concerning in animal bites/scratches) 2
• Other common organisms include:
  • Streptococcus species
  • Staphylococcus species
  • Anaerobes (Bacteroides, Fusobacterium)
  • Capnocytophaga canimorsus

Treatment Algorithm

1. First-line IV therapy: Ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours 1

   • Provides excellent coverage against Pasteurella multocida
   • Covers streptococci, many staphylococci, and anaerobes
   • Appropriate for elderly patients with potentially more severe infections

2. Alternative options (if penicillin allergic):

   • Piperacillin-tazobactam 3.37 g IV every 6-8 hours 1
   • For severe penicillin allergy: Combination therapy with:
     • Doxycycline 100 mg IV every 12 hours (excellent activity against P. multocida) 1 plus
     • Clindamycin 600 mg IV every 6-8 hours (for streptococci, staphylococci, and anaerobes) 1

3. Duration of therapy:

   • Initial IV therapy until clinical improvement
   • Total course of 5-7 days, extending if infection has not improved 1

Special Considerations for This Patient

Age-related factors

• At 89 years old, this patient has higher risk for complications
• May have diminished immune response
• Potentially reduced renal function requiring dose adjustment

Monitoring

• Daily assessment of:
  • Extent of erythema (mark borders to track progression/resolution)
  • Systemic symptoms (fever, vital signs)
  • Laboratory parameters (WBC, renal function)

Adjunctive Measures

• Elevation of the affected extremity to reduce edema 1
• Consider blood cultures if systemic symptoms present 1
• Assess for deeper infection if poor response to initial therapy

Common Pitfalls to Avoid

1. Inadequate coverage for Pasteurella multocida

   • P. multocida infections progress rapidly (12-24 hours after injury) 2
   • Untreated infections can lead to osteomyelitis or septicemia 3

2. Focusing only on MRSA coverage

   • While MRSA is important in many skin infections, animal bite cellulitis is primarily caused by other organisms 4
   • Standard MRSA coverage alone (e.g., vancomycin) would miss critical pathogens like P. multocida

3. Delayed treatment

   • Animal bite/scratch infections can progress rapidly
   • Prompt initiation of appropriate antibiotics is essential to prevent complications

4. Overlooking the need for surgical evaluation

   • Deep puncture wounds may require exploration, irrigation, or debridement
   • Assess for retained foreign material or abscess formation

By following this approach with ampicillin-sulbactam as the primary IV therapy, you'll provide optimal coverage for the most likely pathogens in this 89-year-old patient with dog scratch cellulitis, minimizing the risk of treatment failure and complications.