How should a cat bite be managed in a patient with a penicillin allergy?

Management of Cat Bites in Penicillin-Allergic Patients

For cat bites in penicillin-allergic patients, use doxycycline 100 mg orally twice daily for 7-10 days as first-line therapy, or alternatively moxifloxacin if doxycycline is contraindicated. 1, 2

Why Cat Bites Require Specific Antibiotic Coverage

Cat bites carry exceptionally high infection risk and require coverage for specific pathogens:

• Pasteurella multocida is isolated in over 50% of cat bite wounds and can cause serious infection with severe complications 3
• Cat bites typically create deep puncture wounds that seed bacteria into deeper tissues, particularly dangerous on the hand where infection can lead to long-term disability 4
• The polymicrobial nature includes anaerobes and aerobes from both the cat's oral cavity and patient's skin, including Pasteurella, Streptococcus, Fusobacterium, and Capnocytophaga species 5
• Cat bites to the hand have the greatest risk of infection among all animal bites 3, 4

Recommended Antibiotic Regimens for Penicillin-Allergic Patients

First-Line: Doxycycline

• Doxycycline 100 mg orally twice daily for 7-10 days is the optimal choice due to superior compliance and excellent anti-inflammatory properties beyond antimicrobial effects 1
• Provides adequate coverage for Pasteurella multocida and most other bite wound pathogens 1

Alternative Options Based on Clinical Scenario

For standard cat bites:

• Moxifloxacin (a respiratory fluoroquinolone) provides superior anaerobic coverage compared to other fluoroquinolones and covers Pasteurella species 6
• Trimethoprim-sulfamethoxazole (1-2 double-strength tablets twice daily) plus metronidazole can be used but requires two medications 1

For severe infections or hand involvement requiring admission:

• Clindamycin 600 mg IV every 8 hours is preferred for severe skin and soft tissue infections in penicillin-allergic patients, providing excellent coverage of Staphylococcus aureus 1
• However, clindamycin has poor coverage of Pasteurella, so consider adding a fluoroquinolone 5

If MRSA is suspected (emerging concern in pet-associated infections):

• Trimethoprim-sulfamethoxazole or clindamycin are appropriate oral options 1
• MRSA infections are increasingly shared between pets and handlers, particularly the USA300 clone 5

Critical Management Steps Beyond Antibiotics

Wound care:

• Copiously irrigate with normal saline using a 20-mL or larger syringe 2, 7
• Explore for tendon or bone involvement and foreign bodies 2
• Remove any devitalized tissue 2
• Document neurovascular function and range of motion of adjacent joints 2

Closure decisions:

• Primary closure may be performed for low-risk wounds, particularly facial wounds for cosmetic reasons 2
• Cat bite puncture wounds, especially on hands, should generally NOT be primarily closed due to high infection risk 4

Additional prophylaxis:

• Evaluate tetanus immunization status 3, 2
• Assess need for rabies postexposure prophylaxis (domestic animals are often unvaccinated) 2, 7
• Rabies prophylaxis consists of immune globulin at presentation and vaccination on days 0,3,7, and 14 7

Common Pitfalls to Avoid

• Do not assume the penicillin allergy is real - approximately 90-95% of patients labeled as penicillin-allergic will test negative on proper testing 1
• Do not use first-generation cephalosporins as alternatives, as they have inferior anaerobic activity and poor Pasteurella coverage 6
• Do not underestimate cat bites to the hand - these require aggressive treatment including prophylactic antibiotics even for minor-appearing wounds 4
• Do not delay treatment - early appropriate antibiotic therapy is key to preventing long-term disability from hand infections 4
• Avoid unnecessary broad-spectrum antibiotics - patients incorrectly labeled as penicillin-allergic have increased rates of C. difficile, MRSA, and VRE infections due to suboptimal antibiotic selection 1

When to Admit

Admit patients with cat bites who have:

• Hand involvement with signs of infection (erythema, swelling, purulent drainage) 4
• Deep tissue involvement or concern for tenosynovitis 4
• Immunocompromised status 7
• Systemic signs of infection 5

Admitted patients require surgical drainage, debridement, copious irrigation, hand elevation, and intensive physiotherapy after a short period of immobilization 4