Are antibiotics given prophylactically for a patient scratch or just a patient bite, especially in patients with compromised immune systems or a history of medical conditions?

Antibiotic Prophylaxis for Animal Bites vs. Scratches

Prophylactic antibiotics are recommended for bites but NOT for simple scratches, unless the scratch meets high-risk criteria such as deep penetration, hand/face location, or occurs in immunocompromised patients. 1

Risk Stratification Algorithm

For Bites (Prophylaxis Indicated):

Preemptive antibiotics for 3-5 days are recommended when ANY of the following high-risk factors are present: 1

• Patient factors:

  • Immunocompromised status 1
  • Asplenia 1
  • Advanced liver disease 1
  • Diabetes 2
  • Pre-existing or resultant edema of affected area 1

• Wound characteristics:

  • Moderate to severe injuries 1
  • Hand, face, foot, or genital location 1, 2
  • Injuries penetrating periosteum or joint capsule 1
  • Deep puncture wounds 1, 2

• Timing consideration:

  • Antibiotics must be given within 24 hours of injury to be effective as prophylaxis 1, 2
  • If presenting ≥24 hours post-bite WITHOUT signs of infection, prophylactic antibiotics should NOT be prescribed 2

For Scratches (Prophylaxis Generally NOT Indicated):

Simple scratches do not warrant prophylactic antibiotics unless they meet the same high-risk criteria as bites (deep tissue involvement, high-risk location, or immunocompromised host). 1

First-Line Antibiotic Recommendation

Amoxicillin-clavulanate 875/125 mg twice daily for 3-5 days is the preferred agent, providing comprehensive coverage against the polymicrobial flora including Pasteurella species (50% of dog bites), Staphylococcus aureus (40%), Streptococcus species (40%), and anaerobes. 1, 2

Alternative Options for Penicillin Allergy:

• Doxycycline 100 mg twice daily (excellent Pasteurella multocida coverage) 2
• Moxifloxacin as monotherapy 2
• Clindamycin plus a fluoroquinolone 2

Infection Rates by Bite Type

Understanding baseline infection risk helps guide prophylaxis decisions: 1

• Cat bites: 30-50% infection rate 1
• Human bites: 20-25% infection rate 1
• Dog bites: 5-25% infection rate 1, 2

Critical Pitfalls to Avoid

• Never use first-generation cephalosporins, macrolides, or penicillinase-resistant penicillins alone - they have poor activity against Pasteurella multocida, present in 50% of dog bite wounds 2
• Do not prescribe prophylactic antibiotics for late presentations (≥24 hours) without infection - this violates guideline recommendations and promotes antibiotic resistance 2
• Do not overlook Capnocytophaga canimorsus risk in asplenic patients or those with liver disease, as this pathogen causes severe sepsis in these populations 2
• Avoid high-pressure irrigation which may spread bacteria into deeper tissue layers 1, 3

Essential Concurrent Management

Beyond antibiotics, every bite/scratch requires: 2

• Thorough irrigation with sterile normal saline 2
• Debridement of necrotic tissue 1, 3
• Tetanus prophylaxis if not current within 10 years 2
• Rabies postexposure prophylaxis consultation with local health officials 1, 2

Human bites require additional consideration for hepatitis B, hepatitis C, and HIV postexposure prophylaxis. 1

Human bites to the hand (closed-fist injuries) warrant special attention due to high complication rates and should receive aggressive early treatment even if initially appearing minor. 4