Cephalexin for Dog Scratch
Cephalexin is NOT the optimal first-line antibiotic for dog scratch or bite wounds—amoxicillin-clavulanate is the preferred agent, but cephalexin can be used for low-risk wounds in patients without penicillin allergy, dosed at 500 mg four times daily for 3-5 days. 1
When to Use Antibiotics for Dog Scratches
The IDSA guidelines specify that preemptive antimicrobial therapy for 3-5 days is recommended for patients who meet ANY of these criteria 1:
- Immunocompromised status
- Asplenia
- Advanced liver disease
- Preexisting or resultant edema of the affected area
- Moderate to severe injuries, especially to the hand or face
- Injuries that may have penetrated the periosteum or joint capsule
For low-risk wounds (superficial scratches not involving hands/feet, presenting within 12-24 hours, in immunocompetent patients), prophylactic antibiotics provide only marginal benefit 1. A meta-analysis found that while antibiotics reduced infection risk (relative risk 0.56), the baseline infection rate for dog bites is only about 16%, and prophylaxis should be limited to high-risk wounds 1.
Why Amoxicillin-Clavulanate is Preferred Over Cephalexin
The critical issue: cephalexin misses Pasteurella multocida, the most common pathogen in dog bites and scratches 1, 2. The IDSA guidelines explicitly recommend amoxicillin-clavulanate (875/125 mg twice daily) as the oral agent of choice for animal bites because it covers both aerobic and anaerobic bacteria, including Pasteurella 1.
Alternative regimens listed in the guidelines include 1:
- Doxycycline 100 mg twice daily (excellent activity against Pasteurella)
- Penicillin plus dicloxacillin (covers Pasteurella and Staphylococcus)
- Clindamycin (misses Pasteurella—poor choice)
When Cephalexin Might Be Acceptable
Despite not being first-line, cephalexin appears in older literature for dog bites 3, 2. It may be reasonable for:
- Very superficial scratches (epidermis only) where Pasteurella penetration is unlikely
- True penicillin allergy where amoxicillin-clavulanate is contraindicated (though note: cross-reactivity risk with cephalexin is <5% even in penicillin allergy 4)
- Cost or availability constraints when amoxicillin-clavulanate is unavailable
Cephalexin Dosing
Per FDA labeling, for skin and soft tissue infections 5:
- Adults: 500 mg every 6 hours (four times daily) OR 500 mg every 12 hours for uncomplicated infections
- Duration: 3-5 days for prophylaxis per IDSA guidelines 1
- Pediatric: 25-50 mg/kg/day in divided doses
Common Pitfalls to Avoid
Don't use cephalexin for hand wounds or deep punctures—these are high-risk and require coverage for Pasteurella and anaerobes 1
Don't prescribe antibiotics for truly superficial scratches in low-risk patients—studies show infection rates of only 1-2% without antibiotics in properly cleaned wounds 6, 7
Don't forget rabies prophylaxis consideration—consult local health officials 1
Don't skip wound care—thorough irrigation with povidone-iodine and debridement is as important as antibiotic choice 6
Clinical Algorithm
For a dog scratch in an adult:
Assess wound risk:
- High-risk: Hand/face, deep, immunocompromised, >12 hours old → Prescribe amoxicillin-clavulanate 875/125 mg twice daily for 3-5 days 1
- Low-risk: Superficial, extremity (not hand), <12 hours, immunocompetent → Consider no antibiotics OR cephalexin 500 mg four times daily for 3-5 days if patient/provider preference
Perform proper wound care: Irrigate thoroughly, debride if needed 6
If true penicillin allergy: Doxycycline 100 mg twice daily is superior to cephalexin for Pasteurella coverage 1
Warn patient about infection signs: Erythema, purulent discharge, fever—return if these develop 8
The evidence strongly favors amoxicillin-clavulanate over cephalexin for any dog bite or scratch requiring antibiotic therapy due to superior pathogen coverage.