What is the recommended dosing of amoxicillin (Amox) for Lyme disease prophylaxis?

Amoxicillin Dosing for Lyme Disease Prophylaxis

For Lyme disease prophylaxis, a single dose of doxycycline is the recommended first-line therapy, not amoxicillin. There is no established amoxicillin prophylaxis regimen in current guidelines. 1, 2

Prophylaxis Recommendations

First-Line Prophylaxis

• Single-dose oral doxycycline is the only recommended prophylactic regimen:
  • Adults: 200 mg as a single dose
  • Children ≥8 years: 4.4 mg/kg (maximum 200 mg) as a single dose 1

When Prophylaxis Should Be Considered

Prophylaxis should only be given when ALL of the following criteria are met:

• Identified Ixodes spp. tick (deer tick)
• Tick attached for ≥36 hours (based on engorgement or known time of attachment)
• Prophylaxis can be started within 72 hours of tick removal
• Local infection rate of ticks with B. burgdorferi is ≥20% (parts of New England, mid-Atlantic states, Minnesota, Wisconsin)
• No contraindications to doxycycline 1

Important Considerations for Amoxicillin

Why Amoxicillin Is Not Recommended for Prophylaxis

• The Infectious Diseases Society of America (IDSA) guidelines explicitly state that amoxicillin should not be substituted for doxycycline for prophylaxis, even in patients for whom doxycycline is contraindicated 1
• Reasons include:
  • No established effective short-course regimen for amoxicillin prophylaxis
  • Likely need for multi-day regimen with associated adverse effects
  • Excellent efficacy of treatment if infection develops
  • Extremely low risk of serious complications from a recognized tick bite 1

Amoxicillin for Treatment (Not Prophylaxis)

If a patient develops Lyme disease and requires treatment (not prophylaxis):

• Amoxicillin dosing for treatment of early Lyme disease (erythema migrans):
  • Adults: 500 mg three times daily for 14 days
  • Children: 50 mg/kg/day in 3 divided doses (maximum 500 mg per dose) for 14 days 1, 2

Special Populations

Pregnant Women and Children <8 Years

• Doxycycline is contraindicated in pregnant women and children <8 years
• Despite this, amoxicillin is still not recommended for prophylaxis in these populations
• The recommended approach is careful observation and prompt treatment if signs of infection develop 1

Clinical Approach to Tick Bites

1. Identify tick species and estimate attachment time
2. Assess local B. burgdorferi prevalence
3. If all high-risk criteria are met and doxycycline is not contraindicated, offer single-dose doxycycline
4. If doxycycline is contraindicated, observation is recommended rather than amoxicillin prophylaxis
5. Monitor for signs of infection (especially erythema migrans) for 30 days
6. If infection develops, treat with appropriate full course of antibiotics 1

Common Pitfalls to Avoid

• Using amoxicillin for prophylaxis when doxycycline is contraindicated (not supported by evidence)
• Providing prophylaxis for low-risk tick bites
• Delaying prophylaxis beyond 72 hours after tick removal
• Confusing prophylaxis regimens with treatment regimens

Remember that the risk of developing Lyme disease after a recognized tick bite, even in highly endemic areas, is low (1-3%), and observation with prompt treatment if infection develops is a reasonable approach 1, 3.