Lyme disease is caused by the spirochete Borrelia burgdorferi and is transmitted by the tick Ixodes scapularis. There are approximately 30,000 reported cases of Lyme disease each year in the United States. Complications from Lyme disease range from mild to life threatening, including rash, arthritis, Bell’s palsy, radiculoneuropathy, encephalitis, and cardiac dysfunction. Prophylactic measures, including a vaccine and oral doxycycline, have been attempted with only moderate success, indicating a need for further research.
This study was a randomized controlled murine trial comparing 4% topical azithromycin with 4% topical doxycycline for Lyme disease prophylaxis after inoculation via infected tick bite. The primary outcome was B. burgdorferi infection at 1 month after exposure confirmed by culture-positive tissue for live spirochetes. Variations in the design included immediate application of the antibiotic at the site of the tick bite, delayed application at the site of tick bite, and application at a site distal to the tick bite. In the primary group (immediate application at the site of the tick bite), 0 of 12 mice in the azithromycin group were culture positive compared with 11 of 12 in the doxycycline group and 11 of 11 in the control group, resulting in 100%, 8%, and 0% protection, respectively (P < .001). Additionally, the 4% azithromycin cream provided 100% protection (0 of 10 culture positive) when applied at a site distal to the tick bite, 100% protection (0 of 12 culture positive) when applied at the tick bite site up to 3 days after tick removal, and 74% protection (3 of 12 culture positive) when applied at the tick bite site 14 days after tick removal.
This study suggests that 4% topical azithromycin cream offers 100% protection both directly and systemically for Lyme disease prophylaxis in a murine model within 3 days of exposure. The authors are hopeful this represents a future treatment option for Lyme disease prevention and that their research will prompt further studies with more test subjects, larger animals, and eventually human trials. Limitations of the study include only using a murine model, the pharmacological differences between azithromycin and doxycycline, and the small sample size.
(Antimicrob Agents Chemother. 2014;58:348–351) J Piesman, A Hojgaard, AJ Ullmann, MC Dolan.
Prepared by Cody Hood, MD, University of Utah Emergency Medicine Resident, Salt Lake City, UT, USA.