What is the recommended prophylaxis for a tick bite?

Tick Bite Prophylaxis

A single dose of doxycycline (200 mg for adults or 4 mg/kg up to 200 mg for children ≥8 years) is recommended for prophylaxis after a tick bite ONLY when ALL of the following high-risk criteria are met: the tick is an adult or nymphal Ixodes scapularis (deer tick) or I. pacificus, attached for ≥36 hours, prophylaxis started within 72 hours of tick removal, and in areas with local Borrelia burgdorferi infection rates in ticks of ≥20%. 1

Specific Criteria for Prophylaxis

Prophylaxis should only be administered when ALL of the following conditions are met:

1. Tick species: Must be Ixodes scapularis (deer tick) or I. pacificus
2. Attachment duration: ≥36 hours
3. Timing: Prophylaxis must be started within 72 hours of tick removal
4. Geographic consideration: Area must have ≥20% local rate of Borrelia burgdorferi infection in ticks
5. Patient eligibility: Not contraindicated for the patient

Contraindications

Doxycycline prophylaxis is contraindicated in:

• Pregnant women
• Children <8 years of age
• Patients with doxycycline allergy 1

When Prophylaxis is NOT Recommended

• For tick bites not meeting ALL criteria above
• For non-Ixodes tick species
• When attachment duration is <36 hours
• When >72 hours have passed since tick removal
• In low-endemic areas (<20% tick infection rates) 1

Alternative Approach When Prophylaxis is Not Indicated

When prophylaxis criteria are not met, a "wait and watch" approach is recommended:

• Monitor for 30 days for symptoms of tick-borne illness
• Watch for erythema migrans rash (must be ≥5 cm in diameter for secure diagnosis)
• Monitor for systemic symptoms (fever, malaise, fatigue, headache, myalgias, arthralgias) 1

Important Considerations

1. Amoxicillin is NOT recommended as prophylaxis for those who cannot take doxycycline 1
2. The efficacy of single-dose doxycycline prophylaxis is approximately 87% when administered within the appropriate timeframe 1
3. The risk of developing Lyme disease after recognized tick bites in endemic areas is only 1-3.2% without prophylaxis 1
4. A European study showed a 67% relative risk reduction with single-dose doxycycline prophylaxis, with a number-needed-to-treat of 51 2

Preventive Measures

All patients should be advised to:

• Use EPA-registered tick repellents
• Wear protective clothing
• Treat clothing with permethrin
• Perform regular tick checks after outdoor activities in endemic areas 1

Common Pitfalls to Avoid

1. Administering prophylaxis when criteria are not met exposes patients to unnecessary antibiotics 1
2. Delayed prophylaxis (>72 hours after tick removal) is ineffective 1, 3
3. Using amoxicillin instead of doxycycline for prophylaxis is not supported by evidence 1
4. Ignoring geographic considerations - prophylaxis is only recommended in areas with ≥20% tick infection rates 1
5. Over-treating tick bites - research suggests that over 40% of I. scapularis tick bites do not warrant antibiotic prophylaxis based on feeding duration assessment 4

Remember that routine prophylaxis or serologic testing is not recommended for all tick bites. The judicious use of prophylaxis based on strict criteria helps prevent unnecessary antibiotic exposure while providing protection for those at highest risk of developing Lyme disease.