What is the first‑line antibiotic for a cat bite in an otherwise healthy adult without known drug allergies or immunosuppression?

First-Line Antibiotic for Cat Bites

Amoxicillin-clavulanate 875/125 mg orally twice daily for 3–5 days is the definitive first-line antibiotic for cat bite wounds in healthy adults. 1, 2

Rationale for Amoxicillin-Clavulanate

This combination provides comprehensive coverage against the polymicrobial flora typical of cat bites, which average 5 bacterial species per wound: 1

• Pasteurella multocida (present in 75% of cat bites) – the most critical pathogen 1, 3
• Staphylococci and streptococci (40% of cases) 1
• Anaerobes including Bacteroides, Fusobacterium, and Peptostreptococcus (65% of cat bites) 1
• Capnocytophaga canimorsus (can cause fatal sepsis in asplenic patients) 1

Cat bites carry a 30–50% infection risk, significantly higher than dog bites, due to deep puncture wounds that inoculate bacteria into tissue planes. 1, 4

Alternative Regimens for Penicillin Allergy

Mild/Non-Anaphylactic Allergy

Doxycycline 100 mg orally twice daily is the preferred alternative, offering excellent P. multocida activity with reliable coverage of staphylococci and anaerobes. 1, 2

Severe/Anaphylactic Allergy

Use dual-agent therapy to ensure adequate coverage: 1, 2

• Fluoroquinolone + Clindamycin: Ciprofloxacin 500–750 mg twice daily (or levofloxacin 750 mg daily) PLUS clindamycin 300 mg three times daily 1, 2
• TMP-SMZ + Metronidazole: Trimethoprim-sulfamethoxazole 160/800 mg twice daily PLUS metronidazole 250–500 mg four times daily 1, 2

The fluoroquinolone or TMP-SMZ covers P. multocida and gram-negatives, while clindamycin or metronidazole provides essential anaerobic coverage. 1

Critical Antibiotics to Avoid

Never use these as monotherapy due to poor or absent P. multocida activity: 1, 2

• First-generation cephalosporins (cephalexin, cefazolin)
• Penicillinase-resistant penicillins (dicloxacillin)
• Macrolides (erythromycin)
• Clindamycin alone
• Second/third-generation cephalosporins without anaerobic coverage (cefuroxime, ceftriaxone)

These agents miss critical pathogens and will result in treatment failure. 1

When to Escalate to Intravenous Therapy

Transition to IV antibiotics if: 2

• Systemic signs develop (fever, lymphangitis, sepsis)
• Deep tissue involvement suspected (tenosynovitis, septic arthritis, osteomyelitis)
• Immunocompromised host with moderate-to-severe injury
• Failed outpatient oral therapy

IV regimen: Ampicillin-sulbactam 1.5–3.0 g every 6–8 hours 1, 2

For penicillin-allergic patients: Carbapenems (ertapenem 1 g daily, meropenem 1 g every 8 hours, or imipenem 1 g every 6–8 hours) 1, 2

High-Risk Wounds Requiring Prophylaxis

Prophylactic antibiotics are mandatory for: 2

• Hand wounds (highest infection and complication risk) 1, 4
• Wounds on feet, face, or near joints 2
• Deep puncture wounds (most cat bites) 4
• Immunocompromised patients 2
• Presentation >8–12 hours after injury with early infection signs 1

Essential Adjunctive Measures

• Wound irrigation: Copious sterile normal saline flush; avoid primary closure of puncture wounds 2
• Tetanus prophylaxis: Update if last dose >5 years ago 2, 5
• Elevation: Keep injured extremity elevated to reduce edema 2
• Rabies assessment: Consider for unknown/feral cats 2

Red-Flag Warning Signs

Instruct patients to return immediately for: 2

• Pain disproportionate to visible injury (suggests periosteal penetration, septic arthritis, or osteomyelitis) 1
• Increasing pain, redness, or swelling
• Purulent drainage
• Fever or red streaks (lymphangitis)
• Decreased range of motion

Hand wounds deserve particular vigilance, as they account for 45% of cat bites and have the highest complication rates. 4

Duration of Therapy

• Uncomplicated prophylaxis: 3–5 days 2
• Early infection: 7–14 days 2
• Complicated infections (osteomyelitis, septic arthritis): 4–6 weeks 1