What is the recommended dose of doxycycline (antibiotic) for preventing Lyme disease after a tick (Ixodes) bite?

Doxycycline Prophylaxis for Tick Bite

For high-risk Ixodes tick bites, administer a single dose of 200 mg doxycycline for adults or 4.4 mg/kg (maximum 200 mg) for children ≥8 years old, given within 72 hours of tick removal. 1

When to Give Prophylaxis

Prophylactic doxycycline should only be administered when ALL of the following criteria are met 1, 2:

• Tick species identified: The tick must be confirmed as an Ixodes scapularis (deer tick) or Ixodes pacificus 1
• Attachment duration ≥36 hours: Estimated by degree of tick engorgement or certainty about exposure time 1
• Highly endemic area: The bite occurred in a region where ≥20% of ticks are infected with Borrelia burgdorferi (parts of New England, mid-Atlantic states, Minnesota, Wisconsin) 1, 2
• Timing window: Prophylaxis can be started within 72 hours of tick removal 1
• No contraindications: Doxycycline is not contraindicated for the patient 1

If the tick bite cannot be classified with high certainty as meeting all criteria, use a wait-and-watch approach rather than prophylaxis. 1

Dosing Regimen

• Adults: Single oral dose of 200 mg 1, 2
• Children ≥8 years: Single oral dose of 4.4 mg/kg, up to maximum 200 mg 1, 2
• Children <8 years and pregnant women: Doxycycline is relatively contraindicated; do NOT substitute with amoxicillin for prophylaxis 1, 3

Evidence Supporting Single-Dose Prophylaxis

The most recent high-quality evidence demonstrates that single-dose doxycycline is highly effective when given promptly. A 2021 European randomized controlled trial showed 67% relative risk reduction in Lyme disease development (number-needed-to-treat of 51), with no serious adverse events reported. 4 Earlier North American trials demonstrated 87% efficacy when doxycycline was given within 3 days of tick removal. 5

Critical timing consideration: Animal model data suggests prophylaxis effectiveness drops dramatically after 24 hours (from 74% to 47% protection) and becomes totally ineffective ≥48 hours post-removal. 5 While the 72-hour window is the guideline standard, earlier administration is strongly preferred. 1

What NOT to Do

• Do not give routine prophylaxis for all tick bites—only high-risk bites meeting all criteria 1, 2
• Do not perform serologic testing on asymptomatic patients after tick bites 1
• Do not substitute multi-day amoxicillin courses for prophylaxis in patients with doxycycline contraindications 1, 3
• Do not give prophylaxis for Ixodes pacificus (West Coast) bites unless local infection rates are documented ≥20% 1

Post-Exposure Monitoring

Regardless of whether prophylaxis is given, instruct patients to monitor for 30 days for 3, 2:

• Erythema migrans: Expanding rash ≥5 cm that develops 3-30 days after bite (typically 7-14 days) 1, 6
• Flu-like symptoms: Fever, headache, muscle pain, joint pain 3
• Swollen lymph nodes 2

A rash appearing within 48 hours of tick removal is likely a hypersensitivity reaction, not Lyme disease. 1 Mark the borders with ink and observe for 1-2 days—erythema migrans will expand while hypersensitivity reactions resolve. 1

Common Pitfalls

• Overprescribing: Recent data suggests prophylaxis may be underprescribed in children but potentially overprescribed in adults who don't meet all high-risk criteria. 7 Strict adherence to all three criteria prevents unnecessary antibiotic use.
• Geographic misapplication: Not all regions have ≥20% tick infection rates; prophylaxis is not indicated in low-prevalence areas even for Ixodes bites. 1, 2
• Delayed administration: The 72-hour window is the outer limit—efficacy decreases substantially with each passing day. 5 Encourage immediate presentation after high-risk tick removal.

Prevention of Future Tick Bites

Counsel patients on 1, 2:

• Use EPA-registered repellents (DEET, picaridin, IR3535, oil of lemon eucalyptus, PMD, 2-undecanone) on skin 1, 2
• Apply permethrin to clothing 1, 2
• Wear protective clothing (long sleeves, pants, closed-toe shoes) in tick-infested areas 2
• Perform daily full-body tick checks 2
• Remove attached ticks promptly with fine-tipped tweezers, grasping close to the skin and pulling upward with steady pressure 1, 3