Rat Bite Fever Treatment
First-Line Antibiotic Therapy
Intravenous penicillin G (12-20 million units/day in divided doses every 4-6 hours) for 3-4 weeks is the treatment of choice for rat bite fever caused by Streptobacillus moniliformis. 1
Alternative Regimens
- Oral penicillin (500 mg four times daily) or amoxicillin (500 mg three times daily) for 7-10 days can be used for less severe cases 2
- Doxycycline (100 mg twice daily) is an effective alternative for penicillin-allergic patients, with successful treatment documented in recent case reports 3
- Cephalexin has demonstrated efficacy in complicated cases, including a six-week course for vertebral osteomyelitis and discitis 4
Clinical Recognition
Key Diagnostic Features
- Classic triad: fever, polyarthralgia/arthritis, and rash (petechial or maculopapular) occurring 3-10 days after rat exposure 5, 3
- Many patients (up to 50%) may not recall or report a rat bite, making exposure history critical 6
- Septic arthritis is a common complication requiring prolonged therapy 5
Diagnostic Challenges
- Blood cultures are frequently negative with standard methods, as S. moniliformis is fastidious and difficult to culture 3, 6
- 16S ribosomal RNA PCR on blood or joint fluid is more sensitive than standard cultures 6
- Specialized immunohistochemistry may be required for definitive identification 3
Treatment Duration Based on Complications
Uncomplicated Disease
- 7-10 days of oral antibiotics for mild cases without complications 2
Complicated Disease
- Septic arthritis: 3-4 weeks of therapy 2
- Osteomyelitis: 4-6 weeks of therapy 2, 4
- Endocarditis: 4 weeks of high-dose IV penicillin (12-20 million units/day) 1
Critical Management Considerations
Wound Care
- Immediately irrigate bite wounds with copious sterile saline 7
- Remove superficial debris without deep debridement 2
- Do not close infected wounds; consider Steri-Strips for approximation of non-infected wounds seen within 8 hours 7
Adjunctive Measures
- Tetanus prophylaxis: Administer 0.5 mL tetanus toxoid intramuscularly if status is outdated or unknown 2, 7
- Rabies prophylaxis: Generally not indicated for rat bites in the United States, as rabies transmission from rodents is extraordinarily rare 7
- Elevate affected extremity if swollen to accelerate healing 2
Follow-Up Protocol
- Outpatients require follow-up within 24 hours by phone or office visit 2, 7
- Consider hospitalization if infection progresses despite appropriate antimicrobial therapy 2
Common Pitfalls
- Delayed diagnosis occurs when clinicians fail to obtain rodent exposure history, particularly in patients presenting with fever and arthritis without obvious bite wounds 6
- Misdiagnosis as autoimmune arthritis, gout, or viral syndrome leads to delayed antibiotic administration and worse outcomes 6
- Inadequate treatment duration for complicated infections (osteomyelitis, septic arthritis) results in treatment failure 5, 4
- Mortality rate reaches 13% without proper treatment, emphasizing the importance of early recognition and appropriate antibiotic therapy 5, 8