What is an appropriate antibiotic choice for an infected scratch?

Antibiotic Choice for Infected Scratch

For an infected scratch, amoxicillin-clavulanate (875/125 mg twice daily) is the first-line antibiotic choice, providing broad-spectrum coverage against the most common pathogens including Staphylococcus aureus, Streptococcus species, and anaerobes. 1

Primary Treatment Recommendation

• Amoxicillin-clavulanate is the preferred agent because it covers both gram-positive cocci (S. aureus and Streptococcus) and provides anaerobic coverage, which is essential for skin and soft tissue infections 1

• The standard adult dosing is 875/125 mg orally twice daily for 7-10 days 1

• For pediatric patients, dose at 25 mg/kg/day of the amoxicillin component in 2 divided doses 1

Alternative First-Line Options

If amoxicillin-clavulanate is unavailable or contraindicated, consider these alternatives:

• Cephalexin 500 mg four times daily provides excellent coverage for methicillin-susceptible S. aureus (MSSA) and streptococci 1

• Dicloxacillin 500 mg four times daily is effective for MSSA and streptococcal infections 1

• Clindamycin 300-450 mg three times daily covers both MSSA and anaerobes, making it useful for penicillin-allergic patients 1, 2

For Penicillin-Allergic Patients

• Clindamycin 300-450 mg three times daily is the preferred alternative, providing coverage against S. aureus, streptococci, and anaerobes 1, 2

• Doxycycline 100 mg twice daily can be used in adults (avoid in children under 8 years) 1

• Trimethoprim-sulfamethoxazole (TMP-SMZ) 1-2 double-strength tablets twice daily is an option, though efficacy data are limited 1

When to Suspect MRSA

Consider MRSA coverage if the patient has:

• Previous MRSA infection or colonization 1
• Recent hospitalization or healthcare exposure 1
• Purulent drainage suggesting staphylococcal abscess 1
• Failed initial therapy with beta-lactams 1

MRSA Treatment Options

• TMP-SMZ 1-2 double-strength tablets twice daily is first-line for outpatient MRSA skin infections 1

• Clindamycin 300-450 mg three times daily is effective if local resistance patterns are favorable 1, 2

• Doxycycline 100 mg twice daily provides MRSA coverage in adults 1

• For severe infections requiring hospitalization: vancomycin 30 mg/kg/day IV in 2 divided doses or linezolid 600 mg twice daily 1

Critical Pitfalls to Avoid

• Do NOT use first-generation cephalosporins (cephalexin, cefazolin) alone if there is any concern for anaerobic involvement or if the scratch is from an animal bite, as they lack anaerobic coverage 3, 4

• Avoid macrolides (erythromycin, azithromycin) as monotherapy due to increasing resistance rates in both S. aureus and Streptococcus species 1, 4

• Penicillinase-resistant penicillins (dicloxacillin, nafcillin) should not be used if the scratch is from an animal bite, as they have poor activity against Pasteurella multocida 3, 4, 5

Special Considerations for Animal Scratches

If the scratch is from a cat, the microbiology changes significantly:

• Amoxicillin-clavulanate 875/125 mg twice daily remains first-line due to excellent coverage of Pasteurella multocida (present in 75% of cat scratches/bites) 3, 4

• Alternative for penicillin allergy: doxycycline 100 mg twice daily has excellent P. multocida activity 3, 4

• Avoid cephalexin, dicloxacillin, and macrolides as they have poor P. multocida coverage 3, 4

When to Escalate to IV Therapy

Consider hospitalization and IV antibiotics if:

• Systemic signs present (fever, lymphangitis, significant cellulitis) 3, 4
• Deep tissue involvement suspected (septic arthritis, osteomyelitis, tenosynovitis) 3, 4
• Hand or finger involvement with signs of deep infection 3, 4
• Failed outpatient oral therapy 1

IV Antibiotic Regimens

• Ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours is first-line for hospitalized patients 3, 4

• Piperacillin-tazobactam 3.37 g IV every 6-8 hours is an alternative 3, 4

• For MRSA coverage: add vancomycin 30 mg/kg/day IV in 2 divided doses 1

Treatment Duration

• Uncomplicated skin infections: 7-10 days total 1, 3

• Deep tissue involvement: 3-5 days IV followed by oral therapy to complete course 3, 4

• Hand infections with complications may require 3-4 weeks for septic arthritis or 4-6 weeks for osteomyelitis 4

Adjunctive Wound Care

• Thorough irrigation and debridement are essential regardless of antibiotic choice 3, 4

• Elevation of affected extremity reduces swelling 4

• Do not primarily close infected wounds; allow healing by secondary intention 4

• Surgical consultation is mandatory if abscess or deep space infection is suspected 3