What is the recommended treatment and medication dosage for a rat bite, including antibiotics, tetanus prophylaxis, and rabies post‑exposure prophylaxis?

Rat Bite Treatment and Dosage

For rat bites, administer amoxicillin-clavulanate 875/125 mg twice daily orally for prophylaxis in high-risk patients, ensure tetanus prophylaxis (Tdap preferred if not previously given within 10 years), and evaluate for rabies post-exposure prophylaxis based on local epidemiology, though rabies prophylaxis is typically not required for rat bites in most settings. 1

Wound Management

Immediate wound care is the cornerstone of treatment:

• Copious irrigation of the wound
• Cautious debridement of devitalized tissue
• Avoid primary closure except for facial wounds, which may be approximated after thorough irrigation and debridement 1

The deep puncturing nature of rodent bites creates an environment conducive to infection, though the natural infection rate without prophylaxis is surprisingly low at approximately 2% 2.

Antibiotic Prophylaxis

When to Use Prophylaxis

Preemptive antibiotic therapy for 3-5 days is recommended for patients who are: 1

• Immunocompromised
• Asplenic
• Have advanced liver disease
• Have preexisting or resultant edema of the affected area
• Have moderate to severe injuries, especially to the hand or face
• Have injuries that may have penetrated the periosteum or joint capsule

Antibiotic Selection and Dosing

First-line: Amoxicillin-clavulanate 875/125 mg orally twice daily 1

This combination provides coverage for the polymicrobial nature of rat bite infections, which commonly include Staphylococcus aureus (the most common isolate), along with various aerobic and anaerobic Gram-positive and Gram-negative bacteria 3.

Alternative oral regimens include: 1

• Doxycycline 100 mg twice daily (good activity against common pathogens; some streptococci resistant)
• Sulfamethoxazole-trimethoprim 160-800 mg twice daily (good aerobic coverage; poor anaerobic activity)
• Moxifloxacin 400 mg daily (monotherapy option with anaerobic coverage)

For established infections requiring IV therapy: 1

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours IV
• Piperacillin-tazobactam 3.37 g every 6-8 hours IV

Duration

7-10 days for prophylaxis or treatment of established infection 1

Tetanus Prophylaxis

Tetanus toxoid must be administered to patients without toxoid vaccination within 10 years. 1

• Tdap (tetanus, diphtheria, pertussis) is preferred over Td if not previously given 1
• This is mandatory as most rat bite patients are deficient in tetanus immunity 2

Rabies Post-Exposure Prophylaxis

Consultation with local health officials is recommended to determine if rabies vaccination should be initiated. 1

In most settings, rabies prophylaxis is usually not required for rat bites as rats are not significant rabies vectors 2. However, if indicated based on local epidemiology:

For Previously Unvaccinated Patients:

Reduced 4-dose vaccine schedule: 4, 5, 6

• Human diploid cell vaccine (HDCV) or purified chick embryo cell vaccine (PCECV)
• 1 mL intramuscularly on days 0,3,7, and 14
• Plus rabies immunoglobulin (RIG) infiltrated into and around the wound

For Previously Vaccinated Patients:

2-dose series on days 0 and 3 (no RIG needed) 4

For Immunocompromised Patients:

5-dose series remains unchanged (days 0,3,7,14, and 28) with RIG 4

Common Pitfalls to Avoid

• Over-prescribing antibiotics: The natural infection rate is only 2% without prophylaxis 2, so reserve antibiotics for high-risk patients
• Wrong antibiotic selection: Avoid narrow-spectrum agents like cephalexin or dicloxacillin alone, as 72.5% of rat bite infections are polymicrobial 3
• Primary closure of wounds: This increases infection risk; facial wounds are the exception 1
• Forgetting tetanus: This is mandatory and often overlooked 2
• Unnecessary rabies prophylaxis: Rats are not significant rabies vectors in most regions; consult local health authorities 1, 2

Bacterial Considerations

Rat bite wounds harbor approximately 22 different bacterial species across 18 genera 3. While Staphylococcus aureus is most common, the majority of infections are polymicrobial, necessitating broad-spectrum coverage when antibiotics are indicated. Common isolates include S. epidermidis (43% in one study), Bacillus subtilis, diphtheroids, and alpha-hemolytic Streptococcus 2.