What antibiotics (Abx) are recommended for a cat bite in a patient with a penicillin (pcn) allergy?

Antibiotic Recommendations for Cat Bite in Patients with Penicillin Allergy

For patients with penicillin allergy who have sustained a cat bite, doxycycline is the first-line antibiotic treatment of choice due to its excellent coverage against Pasteurella multocida and other common cat bite pathogens.

Understanding Cat Bite Infections

Cat bites carry a high risk of infection (75% contain Pasteurella multocida) and require prompt antibiotic treatment. The microbiology typically includes:

• Pasteurella multocida (present in 75% of cat bites) 1
• Staphylococcus species (40% of bites)
• Streptococcus species (40% of bites)
• Anaerobes (Bacteroides, Fusobacterium, Porphyromonas species)
• Capnocytophaga canimorsus (less common but potentially serious)

First-Line Treatment Options for Penicillin-Allergic Patients

Doxycycline

• Dosage: 100 mg orally twice daily for 10-14 days 2
• Rationale: Excellent coverage against Pasteurella and other common pathogens in cat bites 3
• Advantages: Once-daily dosing possible after initial day, good tissue penetration

Alternative Options

1. Clindamycin

   • Dosage: 300-450 mg orally three times daily for 7-10 days 3, 4
   • Good for anaerobic coverage but may have inadequate coverage against Pasteurella alone
   • Consider adding a fluoroquinolone for better gram-negative coverage

2. Trimethoprim-sulfamethoxazole

   • Consider for patients who cannot take doxycycline
   • May need addition of clindamycin for anaerobic coverage

3. Fluoroquinolones (e.g., ciprofloxacin, moxifloxacin)

   • Consider for more severe infections or when other options aren't suitable
   • Provides good gram-negative coverage including Pasteurella

Treatment Considerations Based on Allergy Type

The approach should be guided by the nature of the penicillin allergy:

1. For immediate/severe (Type I) penicillin hypersensitivity:

   • Avoid all β-lactams including cephalosporins
   • Use doxycycline as first-line therapy 3

2. For non-severe, delayed-type penicillin allergy:

   • Consider cephalosporins with dissimilar side chains as they have low cross-reactivity (approximately 2% rather than historically cited 10%) 5, 6
   • Cephalexin may be an option if there was no immediate hypersensitivity reaction to penicillin 5

Special Considerations

• Wound management: Thorough cleaning, debridement if necessary, and consideration of wound closure timing are essential alongside antibiotic therapy
• Immunocompromised patients: Consider more aggressive therapy with IV antibiotics
• Severe infections: Hospitalization and parenteral therapy may be required
• Monitoring: Assess for improvement within 48-72 hours; consider alternative diagnosis or treatment if no improvement

Potential Complications

Cat bites can lead to serious complications if not properly treated:

• Deep tissue infections
• Tenosynovitis (especially with hand wounds)
• Septic arthritis
• Osteomyelitis
• Bacteremia and endocarditis (rare but reported) 7

Common Pitfalls to Avoid

1. Underestimating cat bites: Cat bites have a higher infection rate (20-80%) than dog bites (3-18%) 1
2. Delayed treatment: Cat bites should receive prompt antibiotic therapy due to high infection risk
3. Inadequate coverage: Ensure chosen antibiotic covers Pasteurella multocida
4. Insufficient duration: Complete the full course of antibiotics (10-14 days typically recommended)
5. Overlooking hand injuries: Cat bites to the hand carry particularly high risk and may require surgical consultation

Remember that while penicillin allergy is commonly reported (approximately 10% of population), clinically significant allergies are much less common (<5%), and many patients labeled as penicillin-allergic can safely receive β-lactams after appropriate evaluation 6.