Single-dose doxycycline prevented Lyme disease after an Ixodes scapularis tick bite.

P a t i e n t s 506 patients who were ≥ 12 years of age; had removed an attached I. scapularis tick from their bodies in the previous 72 hours; and were bitten in Westchester County, New York. Exclusion criteria were clinical signs of Lyme disease, current or recent completion of an antibiotic course that is effective against Borrelia burgdorferi, vaccination against Lyme disease, nonsubmission of the removed tick, or pregnancy or lactation. In 482 patients (median age 41 y, 53% men), the ticks were confirmed to be I. scapularis ticks. 85% of these patients completed follow-up. I n t e r v e n t i o n Patients were allocated to doxycycline, two 100-mg capsules (n = 235), or placebo (n = 247).