Prophylactic Doxycycline for Lyme Disease

Abstract & Commentary

Source: Nadelman RB, et al. Prophylaxis with single-dose doxycycline for the prevention of Lyme disease after an Ixodes scapularis tick bite. N Engl J Med 2001:345:79-84.

This study was conducted in Westchester, NY, an area hyperendemic for Lyme disease, and spanned a decade. The authors recruited adult patients who had removed attached Ixodes scapularis, or deer ticks, within the previous 72 hours. The subjects were randomized in a double-blind fashion to receive either a single dose of doxycycline 200 mg or placebo. The authors followed the subjects for six weeks to detect erythema migrans (the rash pathognomonic of Lyme disease) and seroconversion.

The authors randomized 482 subjects with confirmed I. scapularis bites, some of whom had multiple tick bites. Erythema migrans was noted in one of 235 doxycyline-treated patients (0.4%) vs. eight of 247 controls (3.2%), a statistically significant difference (P < 0.04). The authors estimate the efficacy of treatment to be 87% (95% confidence interval; 25%—98%). Side effects, primarily nausea and vomiting, were noted in one-third of treated subjects. No patient went on to develop later manifestations of Lyme disease. The authors conclude that a single 200 mg dose of doxycycline, given within 72 hours of an I. scapularis tick bite, is effective for prevention of Lyme disease.

Comment by David J. Karras, MD, FAAEM, FACEP

Because this article received considerable attention even prior to its publication in one of the country’s most prominent medical journals, emergency physicians likely are to be confronted by patients with recent tick bites who request prophylactic antibiotic therapy. Indeed, the authors provide compelling evidence for complying with such requests, given certain caveats. First, not all tick bites are from I. scapularis, and physicians should make reasonable attempts to have the patient describe the offending tick. A large, easily grasped tick is very unlikely a deer tick, which is, at most, a few millimeters across. Second, while Lyme disease is endemic in most mid-Atlantic states, New England, and Wisconsin, it is rare in the Rocky Mountain states and many other areas. Therapy should be tailored to the risk of infection from exposure based on local epidemiologic data.1 Treatment with this dose of doxycycline was not entirely benign, and gastrointestinal side effects frequently were reported. Finally, bear in mind that this was a small study, with a correspondingly wide efficacy estimate (as low as 25%). Although the Infectious Disease Society of America recently has recommended that patients bitten by deer ticks should not receive prophylactic antibiotics, this landmark study changes everything.2


1. Shapiro ED. Doxycycline for tick bites—Not for everyone. N Engl J Med 2001;345:133-134.

2. Wormser GP, et al. Practice guidelines for treatment of Lyme disease. Clin Infect Dis 2000;31(Suppl 1):1-14.