Single-dose doxycycline,
does it really help with Prevention of erythema migrans at the tick-bite site?
research showsThe grade is B. In a double-blind placebo-controlled trial in a hyperendemic New York area, bite-site erythema migrans occurred in 1/235 (0.4%) with doxycycline and 8/247 (3.2%) with placebo, efficacy 87% (95% CI 25%-98%). The absolute difference was 2.8 percentage points, or about 36 people treated to prevent one event. Only nine events occurred, the primary efficacy analysis retained 482 of 506 randomized bite episodes with confirmed I. scapularis ticks, and no independent replication exists, giving B with 72 points.
ads claimThe result does not mean everyone with any tick bite should take doxycycline or that all Lyme disease is certainly prevented. It tested one tick species, an endemic area, dosing within 72 hours, and bite-site erythema migrans.
Useful facts when choosing a product
- Participants swallowed two 100-mg doxycycline capsules once under direct observation.
- The efficacy denominator represented 482 confirmed tick-bite episodes; six people enrolled in two different years.
- Verdict 2473 is C with 54 points for permethrin-treated work clothes reducing tick bites; this verdict concerns post-bite antibiotic prevention of erythema migrans.
What the research actually shows
The hospital pharmacy prepared two 100-mg doxycycline capsules or two identical lactose-placebo capsules and distributed them from a 1:1 randomization list; participants and study staff were unaware of vial contents. There were 506 randomized bite episodes, including six people enrolled in different years twice, while the paper's primary intention-to-treat efficacy set retained 482 episodes with confirmed I. scapularis ticks. Only 431/482 (89.4%) completed all three visits. The study ran from 1987 to 1996 and had no modern trial registration. New York State's Tick-Borne Diseases Institute and CDC grants supported it. The group author Tick Bite Study Group included Susan Bittker, Denise Cooper, Diane Holmgren, Charles Pavia, and Ira Schwartz.
Why this is classified as B (72)
A publicly funded double-blind trial found a large reduction in clinical erythema migrans, but few events, exclusion of 24 randomized bite episodes from efficacy analysis, and absent independent replication give B with 72 points.
Counterpoint. The grade is not a prescribing recommendation; baseline risk, adverse effects, tick species, engorgement, and local epidemiology must be considered.
Rejudgment record. Cross-check applied — The NEJM report and PubMed record were checked for the group author, primary endpoint, 506 randomized and 482 efficacy-analyzed episodes, pharmacy randomization and masking, funding, and adverse events
| Endpoint | H | Hard endpoint - actual events such as death |
| Replication | R1 | Single confirmatory trial |
| Independence | I2 | Decisive evidence is publicly or non-profit funded |
| Effect size | E+ | Meets the clinically important threshold |
The scoring table and the verdict agree (B).
Sub-claim grades by effect
This ingredient is marketed for several effects. A single overall grade blends strong and weak claims together, so each effect is graded separately here. The overall grade reflects the strongest disconfirming or core claim.
| Effect (sub-claim) | Grade | Basis |
|---|---|---|
| Prevention of bite-site erythema migrans | B | Rates were 0.4% versus 3.2%, efficacy 87%. |
| Prevention of objective disseminated Lyme disease | ? | No neurologic, cardiac, or joint manifestations occurred in either group, leaving no events for a direct estimate. |
Cross-check — Codex and Claude
Evidence Table
| Study | Design | Sample | Funding | Endpoint | Result | Weight |
|---|---|---|---|---|---|---|
| Nadelman RB, Nowakowski J, Fish D, Falco RC, Freeman K, McKenna D, Welch P, Marcus R, Agüero-Rosenfeld ME, Dennis DT, Wormser GP; Tick Bite Study Group. 2001 | Double-blind randomized identical-placebo-controlled trial | 247 | New York State Department of Health Tick-Borne Diseases Institute and CDC grants | Erythema migrans at the bite site within six weeks | 1/235 (0.4%) versus 8/247 (3.2%), efficacy 87% (95% CI 25%-98%). | Only direct double-blind confirmatory trial |
Receipt — 1 References
All 1 cited sources were verified for existence at the original page (as of 2026-08-15).
Reviewed and approved: Chamgap Editorial Team · Approval date: 2026-08-15 · Corrections: none
Cite this verdict
[Chamgap] Single-dose doxycycline x prevention of erythema migrans after a tick bite — Evidence Grade B·72. 1 cited sources checked. Source: https://chamgap.com/en/verdicts/immunity/single-dose-doxycycline-tick-bite-erythema-migrans/ · CC BY 4.0CC BY 4.0 — free to use with attribution; do not distort grades, numbers, or verdict meaning.
What this document does and does not do
Chamgap is an information source. It reports what research has and has not confirmed; it does not tell readers what to take or buy. That decision belongs to readers and, when needed, medical or legal professionals. This verdict reflects literature available up to the search date and may change as new research appears. Nothing here is medical advice.