What is the recommended prophylaxis for Lyme (Lyme disease) disease after a tick bite?

Lyme Disease Prophylaxis After Tick Bite

A single 200 mg dose of doxycycline is recommended for prophylaxis after a tick bite, but ONLY when all five strict criteria are simultaneously met. 1, 2

Five Mandatory Criteria for Prophylaxis

All of the following must be present to justify prophylaxis:

• Tick species identification: The tick must be reliably identified as an adult or nymphal Ixodes scapularis (deer tick/blacklegged tick) in the Northeast or Upper Midwest, or Ixodes pacificus in the West (though prophylaxis is generally not recommended for I. pacificus due to infection rates <20%). 1, 2

• Attachment duration ≥36 hours: The tick must have been attached for at least 36 hours, estimated by the degree of engorgement with blood or certainty about the time of exposure. 1, 2

• Timing within 72 hours: Prophylaxis must be initiated within 72 hours of tick removal, as there is no data supporting efficacy beyond this window. 1, 2

• Geographic endemicity: The bite must have occurred in an area where ≥20% of ticks carry Borrelia burgdorferi—this generally includes parts of New England, mid-Atlantic states, Minnesota, and Wisconsin, but not most other U.S. locations. 1, 2

• No contraindications to doxycycline: The patient must not be pregnant, breastfeeding, or under 8 years of age. 1, 2, 3

Dosing Regimen

• Adults: Single dose of 200 mg doxycycline orally 1, 2

• Children ≥8 years: Single dose of 4 mg/kg (maximum 200 mg) orally 1, 2

Special Populations and Contraindications

• Children <8 years: Do NOT give doxycycline prophylaxis due to tooth staining and bone development risks. Instead, perform prompt tick removal and observe closely for 30 days. 2, 3

• Pregnant and breastfeeding women: Do NOT give doxycycline prophylaxis. Use watchful waiting and treat with amoxicillin if Lyme disease develops. 1, 2, 3

• Critical caveat: Do NOT substitute amoxicillin for doxycycline in contraindicated patients for prophylaxis purposes, as there is no evidence for an effective short-course prophylaxis regimen with alternative agents, and the risk of serious complications from a recognized tick bite is extremely low. 1, 4

When Prophylaxis Is NOT Recommended

• Routine prophylaxis for all tick bites is NOT recommended—the criteria above must ALL be met. 1, 5

• Do not test the tick for B. burgdorferi, as this does not reliably predict clinical infection. 5

• Do not perform serologic testing on asymptomatic patients after tick bites. 1, 5

• If any single criterion is not met, observation is the appropriate strategy rather than prophylaxis. 4

Post-Prophylaxis Monitoring (Critical)

Even with prophylaxis, patients must be monitored for 30 days:

• Watch for erythema migrans: An expanding red rash at the bite site or elsewhere on the body, which may appear as a "bull's-eye" pattern. 2, 4

• Watch for systemic symptoms: Fever, chills, fatigue, body aches, headache, and swollen lymph nodes. 2

• Seek immediate medical attention if an expanding rash or flu-like symptoms develop, as the single prophylactic dose does not guarantee prevention. 2, 4

If Lyme Disease Develops Despite Prophylaxis

Treatment regimens differ from prophylaxis:

• Adults with erythema migrans: Doxycycline 100 mg twice daily for 14 days (range 10-21 days) 2, 5

• Children ≥8 years with erythema migrans: Doxycycline 4 mg/kg/day in 2 divided doses (maximum 100 mg per dose) for 14 days 2, 5

• Children <8 years with erythema migrans: Amoxicillin 50 mg/kg/day in 3 divided doses (maximum 500 mg per dose) for 14-21 days 2, 5

Common Pitfalls to Avoid

• Do not assume prior Lyme disease provides immunity—patients with previous Lyme disease can be reinfected and should receive prophylaxis using the same criteria and dosing. 4

• Do not give prophylaxis outside the 72-hour window—efficacy data does not support this practice. 1, 2

• Do not use amoxicillin for prophylaxis—even in patients who cannot take doxycycline, as there is no validated short-course regimen. 1, 4

• Do not prescribe prophylaxis for I. pacificus bites in most Western U.S. regions, as infection rates are typically <20%. 4

Supporting Evidence Quality

The most recent high-quality evidence from a 2021 European randomized controlled trial demonstrated that single-dose doxycycline reduced Lyme disease risk by 67% (number-needed-to-treat = 51) with no serious adverse events. 6 A 2021 meta-analysis of 3,766 individuals confirmed a pooled risk ratio of 0.38 for unfavorable events with prophylaxis, with the single 200 mg doxycycline dose showing the strongest benefit (RR 0.29). 7 These findings support the long-standing IDSA guideline recommendations from 2006, which remain the standard of care. 1