What is the treatment for Rocky Mountain spotted fever (RMSF) and other rickettsial diseases?

Treatment of Rocky Mountain Spotted Fever and Rickettsial Diseases

Doxycycline is the drug of choice for all tickborne rickettsial diseases in patients of all ages, including children under 8 years, and must be initiated immediately when rickettsial disease is suspected—never delay treatment while awaiting laboratory confirmation. 1

Dosing Regimen

Adults

• 100 mg twice daily (orally or intravenously) 1, 2, 3

Children weighing <100 lbs (45 kg)

• 2.2 mg/kg body weight twice daily (orally or intravenously), maximum 100 mg per dose 1, 2

Route Selection

• Oral therapy is appropriate for early-stage disease in outpatients who can tolerate oral medications 1, 2
• Intravenous therapy is indicated for severely ill hospitalized patients, particularly those who are vomiting or obtunded 1, 2

Duration of Treatment

• Continue for at least 3 days after fever subsides and until evidence of clinical improvement is noted 1, 2
• Minimum total course: 5-7 days for Rocky Mountain spotted fever and ehrlichiosis 1
• 10-14 days for anaplasmosis if concurrent Lyme disease coinfection is suspected 1, 2
• Severe or complicated disease may require longer treatment courses 1, 2

Critical Timing Considerations

Delay in treatment leads to severe disease and death—this is the most important clinical pitfall to avoid. 1

• Fever typically subsides within 24-48 hours after initiating doxycycline when started in the first 4-5 days of illness 1, 2
• If fever persists >48 hours after starting doxycycline, consider alternative diagnoses, coinfection, or that the condition is not a rickettsial disease 1
• Severely ill patients with multiple organ dysfunction may require longer than 48 hours before clinical improvement 1, 2

Special Populations

Children Under 8 Years

• Doxycycline is recommended by the American Academy of Pediatrics and CDC as the treatment of choice for all ages, including children <8 years 1
• Limited courses of doxycycline for rickettsial disease pose negligible risk for tooth staining compared to the life-threatening nature of untreated RMSF 1
• Multiple exposures increase tooth staining risk, but short-term use (5-7 days) has minimal effect on permanent teeth 1

Pregnancy

• Doxycycline should still be used when rickettsial disease is suspected, as treatment at recommended doses and duration is unlikely to pose substantial teratogenic risk 1
• Chloramphenicol may be considered as an alternative for Rocky Mountain spotted fever in pregnant patients with severe doxycycline allergy, but carries greater risk for death compared to doxycycline 1
• Chloramphenicol is not acceptable for ehrlichiosis or anaplasmosis 1
• Rifampin might be an alternative for mild anaplasmosis in pregnancy 1

Lactation

• Short-term doxycycline use is considered probably safe during breastfeeding 1

Alternative Agents (Only When Doxycycline Cannot Be Used)

• Chloramphenicol: Only for Rocky Mountain spotted fever in patients with severe doxycycline allergy or pregnancy; associated with higher mortality than doxycycline 1
• Rifampin: May be considered for mild anaplasmosis in patients with severe drug allergy or pregnancy 1

What NOT to Do

• Do not use prophylactic doxycycline after tick bite in asymptomatic persons 1
• Do not treat asymptomatic seropositive persons, as antibodies persist for months to years after infection regardless of treatment 1
• Do not wait for laboratory confirmation before initiating treatment—diagnostic tests are not helpful in making timely diagnosis during initial illness stages 1
• Do not use chloramphenicol for ehrlichiosis or anaplasmosis 1

Clinical Approach Algorithm

1. Suspect rickettsial disease based on fever, headache, malaise, with or without rash, particularly during April-September with tick exposure history 1, 4
2. Initiate doxycycline immediately—do not delay for laboratory confirmation 1, 2
3. Consider concurrent empiric treatment for other life-threatening conditions in the differential (e.g., meningococcemia) while awaiting diagnostic clarification 1
4. Reassess at 48 hours: If no clinical improvement, consider alternative diagnoses or coinfection 1, 2
5. Continue treatment for minimum 3 days after fever resolution and clinical improvement, typically 5-7 days total 1, 2