What oral antibiotic is recommended for a dog bite in a patient with a penicillin allergy?

Oral Antibiotic for Dog Bite with Penicillin Allergy (Hives)

For a patient with hives to penicillin (indicating IgE-mediated allergy), prescribe 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, 2

Why Combination Therapy is Essential

Dog bite wounds require coverage of both aerobic and anaerobic organisms that cannot be achieved with monotherapy in penicillin-allergic patients 1:

• Pasteurella multocida (present in 50% of dog bites) - covered by doxycycline 1
• Staphylococci and Streptococci (present in ~40% of bites) - covered by doxycycline and clindamycin 1
• Anaerobes including Bacteroides, Fusobacterium, Porphyromonas, and Prevotella species (present in ~60% of wounds) - covered by clindamycin or metronidazole 1, 2

Specific Regimen Recommendations

First-Line Option:

• Doxycycline 100 mg PO twice daily PLUS Clindamycin 300 mg PO three times daily 1, 2

Alternative Fluoroquinolone-Based Regimens:

If doxycycline is contraindicated, use one of these alternatives 1:

• Moxifloxacin 400 mg daily (monotherapy with anaerobic coverage) 1
• Levofloxacin 750 mg daily PLUS Metronidazole 500 mg three times daily 1
• Ciprofloxacin 500-750 mg twice daily PLUS Metronidazole 500 mg three times daily 1

Critical Caveat About Hives and Penicillin Allergy

Since the patient has hives (urticaria) to penicillin, this represents an IgE-mediated immediate-type hypersensitivity reaction 1. This is crucial because:

• Avoid all cephalosporins - up to 10% of patients with immediate penicillin hypersensitivity will also react to cephalosporins 1
• Cephalosporins should NOT be used in patients with anaphylactic-type reactions to penicillin 1

What NOT to Use in This Patient

The following are inadequate for penicillin-allergic patients with dog bites 1, 2:

• First-generation cephalosporins (cephalexin, cefadroxil) - contraindicated due to cross-reactivity AND poor Pasteurella coverage 1, 2
• Clindamycin monotherapy - misses Pasteurella multocida 1, 2
• Macrolides (azithromycin, erythromycin) - poor Pasteurella coverage 1
• Trimethoprim-sulfamethoxazole monotherapy - poor anaerobic coverage 1

Duration of Therapy

• Prophylaxis/early treatment: 3-5 days for high-risk wounds 1, 2
• Established infection: 7-10 days 2
• Complicated infections (septic arthritis, osteomyelitis): 3-6 weeks 2

High-Risk Features Requiring Treatment

Preemptive antibiotic therapy is strongly recommended for patients with 1, 2:

• Immunocompromised status or asplenia
• Advanced liver disease
• Preexisting or resultant edema of affected area
• Moderate to severe injuries, especially to hand or face
• Injuries penetrating periosteum or joint capsule
• Puncture wounds

Additional Essential Management

• Wound irrigation with sterile normal saline and debridement of devitalized tissue 1
• Tetanus prophylaxis if not vaccinated within 10 years (Tdap preferred over Td if not previously given) 1
• Rabies consultation with local health officials to determine if post-exposure prophylaxis is needed 1