Scrub Typhus Management
First-Line Treatment
Doxycycline is the drug of choice for scrub typhus treatment in all patients, including children under 8 years of age, and should be initiated immediately when scrub typhus is suspected based on clinical presentation alone, without waiting for laboratory confirmation. 1, 2, 3
Adult Dosing
- Doxycycline 100 mg twice daily (oral or intravenous) 1, 2, 3
- Continue for at least 3 days after fever subsides and until clinical improvement is evident 1, 2
- Minimum total treatment course: 5-7 days 1, 2
- Severe or complicated disease may require longer courses 1, 2
Pediatric Dosing
- Children <45 kg: Doxycycline 2.2 mg/kg body weight twice daily (oral or intravenous) 1, 2
- Children ≥45 kg: Use adult dosing (100 mg twice daily) 2
- Loading dose option: 4.4 mg/kg as single dose for children <45 kg, then 2.2 mg/kg every 12 hours 2
- Loading dose option: 200 mg as single dose for children ≥45 kg and adults, then 100 mg every 12 hours 2
Critical Timing Considerations
- Expect fever resolution within 24-48 hours of initiating doxycycline 1, 2, 4
- Lack of response within 48 hours should prompt reconsideration of the diagnosis, as this suggests the condition is not a rickettsial disease 1, 2
- Early treatment (before complications develop) significantly reduces morbidity and mortality 4
Alternative Agents
Azithromycin
- Preferred alternative for pregnant women and children when doxycycline is contraindicated 2, 5, 6
- Single 500 mg dose has demonstrated equivalent efficacy to 7-day doxycycline course in mild scrub typhus 7
- Median time to defervescence: 21 hours with azithromycin vs 29 hours with doxycycline 7
- Successfully used in pregnancy without relapse and with favorable outcomes 5
Chloramphenicol
- Dosing: 12.5-25 mg/kg every 6 hours IV (maximum 1 g/dose) 2
- The lower end of dosing range (12.5 mg/kg) is sufficient for most cases 2
- Serum concentration monitoring should be performed when available, especially in children 2
Rifampin
- Dosing: 600 mg once daily for 5 days 8
- Effective alternative in areas with documented doxycycline resistance 8, 6
- Demonstrated equivalent efficacy to doxycycline in controlled trial 8
- Particularly important option in northern Thailand where doxycycline resistance has been documented 6
Common Pitfalls to Avoid
Delayed Treatment
- Never delay treatment while awaiting laboratory confirmation, as delay can lead to severe disease, long-term sequelae, or death 2
- Patients who received anti-scrub antibiotics prior to hospitalization had fewer complications and zero mortality, compared to 6.6% mortality in those treated late 4
- Average duration of illness before presentation in fatal cases: 9.2 days 4
Dental Staining Concerns in Children
- Historical concerns about dental staining should not prevent doxycycline use in children under 8 years 1, 2
- Multiple exposures increase risk, but limited courses (5-7 days) have negligible effect on permanent teeth 1
- Prospective studies demonstrate no substantial tooth discoloration with short courses for rickettsial diseases 1
- Beyond ages 6-7 years, risk is minimal as visible tooth formation is complete 1
Dosing Errors in Children
- Always calculate pediatric doses based on actual body weight, not age alone 2
- Verify suspension concentration before calculating mL doses to avoid underdosing 2
- For 25 mg/5 mL suspension: multiply total mg dose by 0.2 to get mL volume 2
- For 50 mg/5 mL suspension: multiply total mg dose by 0.1 to get mL volume 2
Route of Administration
- Intravenous therapy is indicated for hospitalized patients 1, 2
- Oral therapy is acceptable for outpatients early in disease course who are not vomiting or obtunded 1
- Oral therapy can also be used for stable inpatients who can tolerate oral intake 1