Single dose prophylactic treatment of a tick bite only prevents a Lyme rash
In a recent review entitled “Lyme Disease: Emergency Department Considerations,” the authors recommend using a one-time, single dose of doxycycline for the prophylactic treatment of a tick bite,  despite the fact that there has been only one study exploring the effectiveness of such a limited dosage. The article also neglects to mention that there are doctors who take a different approach and advise against a one-time, single dose. 
by Daniel J. Cameron, MD MPH
The authors cite the 2006 Infectious Diseases Society of America (IDSA) guidelines when making their recommendation that “individuals be treated with a single dose of doxycycline (4 mg/kg in children ≥8 years of age to a maximum 200 mg and 200 mg in adults)”.  Their recommendation applies only to patients meeting the following criteria, “(1) the attached tick is clearly identified as a nymph or adult I. scapularis; (2) the tick has been attached ≥36 hours; (3) local infection rates of ticks with B. burgdorferi is ≥20%; and (4) there are no contraindications to doxycycline.” 
The authors fail to mention that the IDSA single dose of doxycycline approach is based on a single study, which only found a reduction in the number of erythema migrans (EM) rashes. “A study by Nadelman et al. found that patients treated with a single dose of doxycycline developed EM manifestation at a lower rate than the placebo group (0.4% compared to 3.2%, respectively),” according to Applegren from the School of Medicine, University of Missouri.
The review also does not mention the evidence, as put forth by the International Lyme and Associated Diseases Society (ILADS), which finds that a single dose is ineffective in warding off Lyme disease. Such evidence was easily accessible via open access, peer-reviewed journals in PubMed , the Journal’s website,  and the National Guideline Clearing House. 
ILADS 2014 guidelines used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system to conclude that the evidence for a single, 200 mg dose of doxycycline was “sparse, coming from a single study with few events, and, thus, imprecise.” 
There were only 9 EM rashes in the Nadelman study. Nadelman and colleagues were able to reduce the number of rashes from eight to one by prescribing a single 200 mg dose of doxycycline. The “p” value was barely significant at 0.04.
The IDSA guidelines adopted the single, 200 mg dose of doxycycline despite the fact that three previous prophylactic antibiotic trials for a tick bite had failed.
Nadelman’s study had several other limitations:
- It was not designed to detect Lyme disease if the rash were absent.
- The 6-week observation period was not designed to detect chronic or late manifestations of Lyme disease.
- It was not designed to assess whether a single dose of doxycycline might be effective for preventing other tick-borne illnesses such as Ehrlichia, Anaplasmosis, or Borrelia miyamotoi.
Today, patients expect to be informed of their treatment options. The recent review in the Journal of Emergency Medicine  would have been stronger if the authors had disclosed the evidence against using a single, 200 mg dose of doxycycline for prophylactic treatment of a tick bite.
- Applegren ND, Kraus CK. Lyme Disease: Emergency Department Considerations. J Emerg Med, (2017).
- Cameron DJ, Johnson LB, Maloney EL. Evidence assessments and guideline recommendations in Lyme disease: the clinical management of known tick bites, erythema migrans rashes and persistent disease. Expert Rev Anti Infect Ther, 1-33 (2014).
- Wormser GP, Dattwyler RJ, Shapiro ED et al. The clinical assessment, treatment, and prevention of lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis, 43(9), 1089-1134 (2006).
- Cameron DJ, Johnson LB, Maloney EL. Evidence assessments and guideline recommendations in Lyme disease: the clinical management of known tick bites, erythema migrans rashes and persistent disease from Expert Review of Anti-infective Therapy 2014 at https://www.tandfonline.com/doi/full/10.1586/14787210.2014.940900. (Last accessed 1/3/16).
- Evidence assessments and guideline recommendations in Lyme disease: the clinical management of known tick bites, erythema migrans rashes and persistent disease. National Guideline Clearinghouse. Agency for Health Care Research and Quality. Available from: https://www.guideline.gov/content.aspx?id=49320. (Last accessed 10/11/15).