Antibiotic Treatment for Cat Bite and Scratch with Signs of Infection
For a patient with erythema, swelling, and pain after a cat bite and scratch to the hand, start amoxicillin-clavulanate 875/125 mg orally twice daily immediately, as this is the first-line treatment providing optimal coverage against Pasteurella multocida and the polymicrobial flora typical of cat bite infections. 1, 2, 3
Why Amoxicillin-Clavulanate is the Definitive Choice
Amoxicillin-clavulanate is specifically recommended by the Infectious Diseases Society of America as first-line therapy for animal bite infections because it covers the critical pathogens:
- Pasteurella multocida (present in 50-90% of cat bites and scratches) 1, 4, 5
- Staphylococci and streptococci 1, 2
- Anaerobes including Bacteroides species 1, 6
- Other gram-negative organisms 1
The dosing is straightforward: 500/875 mg twice daily orally for established infections. 1
Treatment Duration
- 7-14 days for established infections with erythema, swelling, and pain 3
- Hand wounds require particular attention due to highest infection risk and potential for serious complications including septic arthritis, osteomyelitis, and tendonitis 2, 3
Critical Pitfall: Hand Wounds Require Aggressive Management
Hand bites and scratches have the greatest risk of infection (up to 80% for cat bites) and serious complications. 4, 7 The hand's complex anatomy with multiple tendon sheaths and joint spaces allows rapid spread of infection. 8 P. multocida can cause rapidly developing cellulitis within 12-24 hours and potentially chronic deep tissue infection or osteomyelitis. 8
When to Escalate to IV Therapy
Switch to intravenous antibiotics if: 2, 3
- Systemic signs develop (fever, malaise)
- Deep tissue involvement is suspected
- Severe edema is present
- Patient is immunocompromised
- Infection is not responding to oral therapy within 48-72 hours
IV options include: 1
- Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours (first-line IV)
- Piperacillin-tazobactam 3.37 g every 6-8 hours
- Carbapenems (ertapenem 1 g daily, meropenem 1 g every 8 hours)
Alternative Regimens for Penicillin Allergy
For patients with penicillin allergy: 1, 2, 3
- Doxycycline 100 mg twice daily - excellent P. multocida activity, preferred alternative 1, 2
- Fluoroquinolones (ciprofloxacin 500-750 mg twice daily OR levofloxacin 750 mg daily) - good P. multocida coverage but may miss some anaerobes 1, 3
- TMP-SMZ 160-800 mg twice daily PLUS metronidazole 250-500 mg four times daily - combination provides aerobic and anaerobic coverage 1, 3
Antibiotics to AVOID as Monotherapy
Do not use these as single agents for cat bites/scratches: 1, 2, 3
- First-generation cephalosporins (cephalexin, cefazolin) - miss P. multocida and anaerobes
- Clindamycin alone - misses P. multocida entirely
- Penicillin alone without dicloxacillin - inadequate coverage
- TMP-SMZ alone - poor anaerobic coverage
Essential Adjunctive Measures
Beyond antibiotics, ensure: 2, 3, 7
- Thorough wound irrigation with sterile normal saline
- Elevation of the hand to reduce swelling
- Tetanus immunization status updated if needed
- Rabies risk assessment (especially for unknown or feral cats)
- Avoid primary closure of puncture wounds
Red Flags Requiring Immediate Surgical Consultation
Seek urgent surgical evaluation if: 2, 6
- Deep abscess formation
- Extensive necrosis
- Purulent drainage requiring incision and drainage
- Suspected septic arthritis or osteomyelitis
- Necrotizing fasciitis
Follow-Up Instructions
Patients must return immediately if they develop: 2, 3
- Increasing pain, redness, or swelling
- Purulent drainage
- Fever
- Decreased range of motion
- Red streaking (lymphangitis)
Early follow-up within 24-48 hours is essential to ensure the infection is responding to treatment, as hand infections can progress rapidly. 2
Special Note on Anaerobic Coverage
Recent case reports demonstrate that anaerobes like Bacteroides pyogenes can cause serious intramuscular abscesses from cat bites, emphasizing the importance of both aerobic and anaerobic culture collection and the need for antibiotics with anaerobic coverage. 6 This reinforces why amoxicillin-clavulanate remains superior to alternatives lacking anaerobic activity.