In an otherwise healthy adult male with a cat bite infection of the hand, what is the appropriate antibiotic regimen, including drug, dose, route, and duration?

Cat Bite Infection of the Hand: Antibiotic Regimen

For an adult male with a cat bite infection of the hand, start amoxicillin-clavulanate 875/125 mg orally twice daily for 7-10 days, or if requiring hospitalization due to systemic signs or deep tissue involvement, use ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours for 3-5 days followed by oral amoxicillin-clavulanate to complete the course. 1, 2

Why Amoxicillin-Clavulanate is First-Line

• Amoxicillin-clavulanate provides optimal coverage against the polymicrobial flora of cat bites, including Pasteurella multocida (present in 75% of cat bites), staphylococci, streptococci, and anaerobic organisms. 3, 1, 2

• Cat bite wounds contain an average of 5 different bacterial species, with approximately 60-65% having mixed aerobic and anaerobic bacteria, making broad-spectrum coverage essential. 1, 2

• P. multocida has 100% susceptibility to amoxicillin-clavulanate and is the predominant pathogen requiring systemic coverage. 1, 2

Oral Therapy Dosing

• Amoxicillin-clavulanate 875/125 mg twice daily for 7-10 days is the standard regimen for uncomplicated hand infections. 3, 1

• This duration applies to uncomplicated cellulitis or soft tissue infection without deep structure involvement. 1

Intravenous Therapy for Severe Infections

Indications for hospitalization and IV therapy include: 2, 4

• Systemic signs (fever, lymphangitis)
• Significant cellulitis with erythema and swelling
• Bite over a joint or tendon sheath
• Deep tissue involvement
• Immunocompromised state or smoking history

IV regimen: 3, 1

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours IV is first-line for hospitalized patients
• Alternative: Piperacillin-tazobactam 3.37 g every 6-8 hours IV
• Duration: 3-5 days IV, then transition to oral amoxicillin-clavulanate to complete 7-10 days total

Alternative Regimens for Penicillin Allergy

• Doxycycline 100 mg twice daily has excellent P. multocida activity, though some streptococci may be resistant. 3, 1

• Moxifloxacin 400 mg daily provides monotherapy with good anaerobic coverage. 3

• Ciprofloxacin 500-750 mg twice daily or levofloxacin 750 mg daily have good P. multocida coverage but miss MRSA and some anaerobes. 3, 1

Critical Antibiotics to AVOID

• First-generation cephalosporins (cephalexin, cefazolin) miss P. multocida and anaerobes and should never be used as monotherapy. 3, 1, 2

• Penicillinase-resistant penicillins (dicloxacillin, nafcillin) alone have poor P. multocida activity and will fail. 1, 2

• Clindamycin monotherapy misses P. multocida despite good activity against staphylococci, streptococci, and anaerobes. 3, 1

Special Considerations for Hand Infections

• Hand bites have the highest infection risk and complication rate, including tendosynovitis, septic arthritis, and osteomyelitis. 1, 2, 4

• 30% of cat bite hand infections require hospitalization, with an average length of stay of 3.2 days. 4

• 67% of hospitalized patients require surgical irrigation and debridement, with some requiring multiple operations. 4

• If there is concern for deep space infection, abscess, or involvement of joints/tendons, immediate hand surgery consultation is mandatory in addition to antibiotics. 1, 2

MRSA Coverage Consideration

• If MRSA is suspected based on local epidemiology or patient risk factors, add TMP-SMX 1-2 double-strength tablets twice daily to amoxicillin-clavulanate. 1

• Alternative: Clindamycin 300 mg three times daily as monotherapy if penicillin-allergic (but only if P. multocida is not suspected or has been ruled out). 3

Common Pitfalls

• Do not rely on topical antibiotics alone for cat bite hand infections—systemic coverage is mandatory. 2

• Do not delay treatment, as this can lead to rapid progression to septic arthritis, osteomyelitis, or tendonitis within 12-24 hours. 2, 5

• Erythema and swelling at presentation are associated with increased risk of hospitalization and should prompt aggressive management. 4

• Immunocompromised patients (diabetes, liver disease, asplenia, immunosuppressive therapy) require more aggressive treatment due to risk of disseminated Capnocytophaga canimorsus infection. 2