PROPHYLAXIS
WITH SINGLE-DOSE DOXYCYCLINE FOR THE PREVENTION OF LYME DISEASE AFTER AN IXODES
SCAPULARIS TICK BITE.
Nadelman
RB, et al. N Engl J Med 2001 Jul 12;345(2):79-84.
BACKGROUND:
It is unclear whether antimicrobial treatment after an Ixodes scapularis tick
bite will prevent Lyme disease.
METHODS:
In an area of New York where Lyme disease is hyperendemic we conducted a
randomized, double-blind, placebo-controlled trial of treatment with a single
200-mg dose of doxycycline in 482 subjects who had removed attached I.
scapularis ticks from their bodies within the previous 72 hours. At base line,
three weeks, and six weeks, subjects were interviewed and examined, and serum
antibody tests were performed, along with blood cultures for Borrelia burgdorferi.
Entomologists confirmed the species of the ticks and classified them according
to sex, stage, and degree of engorgement.
RESULTS:
Erythema migrans developed at the site of the tick bite in a significantly
smaller proportion of the subjects in the doxycycline group than of those in
the placebo group (1 of 235 subjects [0.4 percent] vs. 8 of 247 subjects [3.2
percent], P<0.04). The efficacy of treatment was 87 percent (95 percent
confidence interval, 25 to 98 percent). Objective extracutaneous signs of Lyme
disease did not develop in any subject, and there were no asymptomatic
seroconversions. Treatment with doxycycline was associated with more frequent
adverse effects (in 30.1 percent of subjects, as compared with 11.1 percent of
those assigned to placebo; P<0.001), primarily nausea (15.4 percent vs. 2.6
percent) and vomiting (5.8 percent vs. 1.3 percent). Erythema migrans developed
more frequently after untreated bites from nymphal ticks than after bites from
adult female ticks (8 of 142 bites [5.6 percent] vs. 0 of 97 bites [0 percent],
P=0.02) and particularly after bites from nymphal ticks that were at least
partially engorged with blood (8 of 81 bites [9.9 percent], as compared with 0
of 59 bites from unfed, or flat, nymphal ticks [0 percent]; P=0.02).
CONCLUSIONS:
A single 200-mg dose of doxycycline given within 72 hours after an I.
scapularis tick bite can prevent the development of Lyme disease.