What is the appropriate oral doxycycline dosage for a rat bite and scratches?

Doxycycline dosing for rat bites/scratches

For adults with a rat bite/scratch who need oral therapy, use doxycycline 100 mg by mouth twice daily (bid). 1

• When to choose doxycycline:
  • Beta-lactam allergy or intolerance to first-line amoxicillin–clavulanate for animal bites; doxycycline has excellent Pasteurella coverage but variable streptococcal activity, so consider adding anaerobic/streptococcal coverage if cellulitis is present or hand/face wounds are involved 1.
• Duration:
  • Prophylaxis (high-risk wounds per IDSA: hand/face, deep puncture, edema, asplenia/immunocompromise, advanced liver disease, periosteal/joint penetration): 3–5 days 2.
  • Established infection/cellulitis: 7–14 days, tailor to clinical response 2.

Algorithm (prioritizing morbidity, mortality, QOL):

• Clean and irrigate thoroughly; update tetanus; assess need for rabies PEP per local public health (critical to prevent severe outcomes) 2.
• Assess wound risk:
  • Low-risk superficial scratches, no comorbid risks: local care only; no antibiotics.
  • High-risk bite/scratch (any IDSA criteria) or signs of infection: start antibiotics.
    • First-line: amoxicillin–clavulanate 875/125 mg bid (broad aerobic/anaerobic) 1.
    • If penicillin allergy or intolerance: doxycycline 100 mg bid; if cellulitis or hand/face involvement, add metronidazole 500 mg tid or clindamycin 300 mg tid to improve streptococcal/anaerobic coverage (doxycycline alone may miss streptococci) 1.
• Reassess at 48–72 h; escalate if worsening.

Key pitfalls/caveats:

• Doxycycline alone may not cover streptococci; combine as above if significant cellulitis is present 1.
• Consider Capnocytophaga in asplenia—prefer amoxicillin–clavulanate if possible 1.
• Ensure evaluation for rat-bite fever (Streptobacillus moniliformis) if fever, rash, migratory arthralgias; doxycycline 100 mg bid is active but some clinicians prefer penicillin—monitor closely.
• Pediatric dosing (≥8 years) if applicable: 2.2 mg/kg per dose every 12 h (max 100 mg per dose) when doxycycline is chosen [FDA label supports weight-based dosing) 3.
• Counsel to take with water, avoid cation supplements/antacids near dosing; watch for esophagitis and photosensitivity 3.

Evidence framing:

• IDSA 2014 SSTI guideline lists doxycycline 100 mg bid as an oral option for animal bites, noting excellent Pasteurella coverage and variable streptococcal activity; amoxicillin–clavulanate remains first-line; prophylaxis recommended 3–5 days in high-risk wounds 1, 2.