What is the recommended dosage and treatment duration of doxycycline (DOXY) for adults and children older than 8 years with Lyme disease?

Doxycycline for Lyme Disease

Recommended Dosing

For early Lyme disease, treat adults with doxycycline 100 mg orally twice daily for 10-14 days, and children ≥8 years with 4 mg/kg per day in 2 divided doses (maximum 100 mg per dose) for the same duration. 1, 2

Adult Dosing

• Standard dose: 100 mg orally twice daily for 10-14 days 1, 2, 3
• The FDA label specifies 200 mg on the first day (100 mg every 12 hours) followed by 100 mg daily maintenance, though clinical practice guidelines support 100 mg twice daily throughout 3, 1
• 10 days is sufficient when using doxycycline (unlike other agents which require 14 days) 1, 2
• Doxycycline has the critical advantage of treating concurrent Human Granulocytic Anaplasmosis (HGA), which may occur simultaneously with Lyme disease 2

Pediatric Dosing (≥8 years)

• 4 mg/kg per day in 2 divided doses (maximum 100 mg per dose) for 10-14 days 1, 2, 4
• Children >100 pounds should receive adult dosing 3
• Recent evidence suggests doxycycline is safe and effective even in children <8 years for short courses (≤21 days), though amoxicillin remains preferred for this age group 5, 6

Neurologic Manifestations

For neurologic Lyme disease without meningitis (e.g., isolated facial nerve palsy), oral doxycycline 200-400 mg/day in 2 divided doses for 10-28 days is acceptable. 1, 2

• For children ≥8 years with neurologic involvement: 4-8 mg/kg per day in 2 divided doses (maximum 100-200 mg per dose) for 10-28 days 1, 2
• Patients with documented meningitis require parenteral therapy with ceftriaxone 1

Tick Bite Prophylaxis

A single 200 mg dose may be given when ALL of the following criteria are met: 1, 2

1. Tick identified as adult or nymphal Ixodes scapularis
2. Estimated attachment ≥36 hours
3. Prophylaxis can start within 72 hours of tick removal
4. Local infection rate ≥20%
5. No contraindications to doxycycline

• For children ≥8 years: single dose of 4 mg/kg (maximum 200 mg) 2

Administration Guidelines

Administer with 8 ounces of fluid to reduce esophageal irritation. 2, 3

• Can be taken with food or milk to reduce gastrointestinal intolerance without affecting absorption 1, 2, 3
• Warn patients about photosensitivity risk and advise sun avoidance 2, 4
• Patients should avoid lying down for 1 hour after taking doxycycline to prevent esophagitis 7

Contraindications

• Relatively contraindicated in pregnancy and lactation 1, 2
• Relatively contraindicated in children <8 years (though evolving evidence suggests safety for short courses) 1, 2, 5

Critical Pitfalls to Avoid

First-generation cephalosporins (e.g., cephalexin) are completely ineffective against Borrelia burgdorferi and must never be used. 1, 2, 4

• Macrolides (azithromycin, clarithromycin, erythromycin) are significantly less effective than doxycycline and should only be reserved for patients truly intolerant of all first-line agents 1, 2
• Never extend treatment beyond 21 days for early Lyme disease—this is not supported by evidence and does not improve outcomes 2, 8
• Never delay treatment while awaiting laboratory confirmation in suspected cases 2
• Do not prescribe multiple repeated courses for the same episode of Lyme disease 1

Alternative First-Line Agents

When doxycycline is contraindicated or not tolerated:

• Amoxicillin 500 mg orally 3 times daily for 14 days (adults) 1, 2
  • Children: 50 mg/kg per day in 3 divided doses (maximum 500 mg per dose) for 14 days 1, 4
• Cefuroxime axetil 500 mg orally twice daily for 14 days (adults) 1, 2
  • Children: 30 mg/kg per day in 2 divided doses (maximum 500 mg per dose) for 14 days 1, 4

Treatment Duration Evidence

A landmark randomized controlled trial demonstrated that 10 days of doxycycline is equally effective as 20 days, with treatment failure being extremely rare (<1%). 8

• The complete response rate at 30 months was 90.3% for 10-day treatment versus 83.9% for 20-day treatment (not statistically different) 8
• Adding a single dose of IV ceftriaxone to oral doxycycline provided no additional benefit 8

Special Considerations

• If concurrent anaplasmosis is suspected (endemic areas with higher co-infection rates), extend doxycycline treatment to minimum 10 days 2
• Most patients respond promptly and completely; however, complete response may be delayed beyond treatment duration 1, 4
• Patients who are more systemically ill at diagnosis may take longer to achieve complete response 1, 4
• Less than 10% of patients fail to respond to initial antibiotic therapy; rarely is re-treatment required 1, 4