What is the recommended treatment for a dog bite in a patient with a penicillin (pcn) allergy?

Dog Bite Treatment in Penicillin-Allergic Patients

For penicillin-allergic patients with dog bites, use doxycycline 100 mg twice daily PLUS either clindamycin 300 mg three times daily OR metronidazole 500 mg three times daily for 3-5 days. 1

Primary Antibiotic Regimen

The combination therapy approach is essential because dog bite wounds harbor both aerobic and anaerobic organisms that require dual coverage:

• Doxycycline 100 mg PO twice daily PLUS clindamycin 300 mg PO three times daily is the preferred regimen for patients with severe or immediate-type penicillin allergy 1
• This combination provides coverage against Pasteurella multocida (isolated in 50% of dog bites), Staphylococci and Streptococci (found in ~40% of bites), and anaerobes including Bacteroides, Fusobacterium, Porphyromonas, and Prevotella species (present in ~60% of wounds) 1

Alternative Regimens

If the doxycycline-clindamycin combination is not tolerated or contraindicated:

• Moxifloxacin 400 mg daily as monotherapy provides both aerobic and anaerobic coverage 1
• Levofloxacin 750 mg daily OR ciprofloxacin 500-750 mg twice daily PLUS metronidazole 500 mg three times daily 1

Safe Beta-Lactam Options in Penicillin Allergy

For patients with suspected immediate-type penicillin allergy, cephalosporins with dissimilar side chains can be used safely:

• Cefazolin does not share side chains with currently available penicillins and can be used regardless of allergy severity or timing 2
• Carbapenems and monobactams can be administered without prior allergy testing in patients with suspected immediate-type penicillin allergy 2

Critical Pitfall to Avoid

Do NOT use first-generation cephalosporins (like cephalexin), macrolides, or clindamycin monotherapy in penicillin-allergic patients with dog bites, as these provide inadequate coverage of Pasteurella multocida 1. This is a common error, as older literature from the 1980s suggested cephalexin as an alternative 3, 4, but this recommendation predates our current understanding of Pasteurella coverage requirements.

Duration of Therapy

Treatment duration depends on clinical presentation:

• 3-5 days for prophylaxis or early treatment of uncomplicated wounds 1, 5
• 7-10 days for established infection 1
• 3-6 weeks for complicated infections such as septic arthritis or osteomyelitis 1

High-Risk Features Requiring Antibiotic Prophylaxis

Preemptive antibiotic therapy is strongly indicated for patients with:

• Immunocompromised status 1, 5
• Asplenia 1, 5
• Advanced liver disease 1, 5
• Preexisting or resultant edema of the affected area 1, 5
• Moderate to severe injuries, especially to the hand or face 1, 5
• Injuries penetrating the periosteum or joint capsule 1, 5

Additional Management Essentials

Beyond antibiotics, comprehensive wound management includes:

• Wound irrigation with copious sterile normal saline and removal of superficial debris 1, 6
• Tetanus prophylaxis if not vaccinated within the past 10 years, preferably with Tdap 1, 5
• Follow-up within 48-72 hours to assess for signs of infection and evaluate wound healing 5
• Rabies risk assessment in consultation with local health officials, with observation of healthy dogs for 10 days 5

Wound Closure Considerations

• Primary closure is generally NOT recommended for dog bite wounds except for facial wounds, which should receive copious irrigation, cautious debridement, preemptive antibiotics, and primary closure for optimal cosmetic results 5
• Non-facial wounds may be approximated rather than fully closed 5