What is the recommended dosage of doxycycline (DOXY) in mL for scrub typhus treatment based on age and body weight?

Doxycycline Dosing for Scrub Typhus Treatment

For scrub typhus treatment, doxycycline should be dosed at 2.2 mg/kg body weight twice daily for children under 45 kg, and 100 mg twice daily for those 45 kg or above, administered orally or intravenously for at least 3 days after fever subsides with a minimum 5-7 day course. 1

Converting mg/kg to mL Volume

To calculate the volume in mL, you need to know the concentration of your doxycycline syrup formulation. Common pediatric formulations include:

• If using 25 mg/5 mL suspension: Multiply the total mg dose by 0.2 to get mL
• If using 50 mg/5 mL suspension: Multiply the total mg dose by 0.1 to get mL

Weight-Based Dosing Algorithm

Children Under 45 kg (99 pounds)

• Loading dose: 4.4 mg/kg as a single dose 2
• Maintenance dose: 2.2 mg/kg every 12 hours 2, 1, 3
• Example: A 20 kg child would receive:
  • Loading: 88 mg (approximately 17.6 mL if using 25 mg/5 mL suspension)
  • Maintenance: 44 mg every 12 hours (approximately 8.8 mL if using 25 mg/5 mL suspension)

Children 45 kg or Above and Adults

• Loading dose: 200 mg as a single dose 2
• Maintenance dose: 100 mg every 12 hours 2, 1

Treatment Duration

Continue doxycycline for at least 3 days after fever subsides, with a minimum total treatment course of 5-7 days. 1, 3 Patients typically respond within 24-48 hours; lack of response should prompt consideration of alternative diagnoses. 1

Critical Safety Considerations

• Do not delay treatment while awaiting laboratory confirmation, as delay can lead to severe disease, long-term sequelae, or death. 1
• Dental staining concerns should not prevent use in children under 8 years for short treatment courses like scrub typhus. 1, 3 The American Academy of Pediatrics confirms that short-term doxycycline does not cause permanent tooth staining or enamel hypoplasia. 3
• Administer with a full glass of water to reduce risk of esophagitis and esophageal ulceration. 3
• Avoid co-administration with antacids containing aluminum, calcium, or magnesium; separate by at least 2-3 hours. 3

Alternative Agents

If doxycycline is contraindicated or unavailable:

• Azithromycin: Single 500 mg dose for adults has shown equivalent efficacy to 7-day doxycycline course 4, and is preferred in pregnancy 5, 6
• Rifampin: 600 mg once daily for 5 days shows equivalent efficacy to doxycycline 7
• Chloramphenicol: 12.5-25 mg/kg every 6 hours IV (maximum 1 g/dose) 2

Common Pitfalls to Avoid

• Underdosing in children: Always calculate based on actual body weight, not age alone
• Premature discontinuation: Even if fever resolves quickly, complete the minimum 5-7 day course 1
• Failing to consider scrub typhus empirically: In endemic areas during tick season, include doxycycline in initial empirical therapy for febrile patients to reduce morbidity and mortality 6
• Not accounting for formulation concentration: Always verify your syrup concentration before calculating mL doses