A new study finds applying azithromycin topically within 72 hours after a tick bite does not prevent Lyme borreliosis.
The prevention of Lyme disease is a growing concern. Research indicates that bacteria injected in the skin by an infected tick multiply for several days at the site of the bite before migrating to other parts of the body. In a laboratory setting, the drug azithromycin applied topically prevented the bacteria from multiplying.
Researchers in Germany tested the hypothesis that using azithromycin on adults bitten by ticks would reduce the number of people who developed Lyme borreliosis. The randomized, double-blind, placebo-controlled study was recently published in The Lancet Infectious Diseases.
The study involved 1371 adults and was conducted in 23 medical clinics over a period of 17 months. Participants were asked to apply one drop of cream to the site of the tick bite twice daily for three consecutive days within 72 hours of being bitten by a tick. Once group received a 10% concentration of azithromycin while the other was given a placebo similar in color, texture, and odor. The results were evaluated based on the appearance of a skin rash, the development of antibodies, and blood serum testing.
At the 8-week mark, 11% of patients developed a skin rash or tested positive for borreliosis antibodies in each group. Given the lack of difference between the control and the placebo group, the study was stopped.
Lyme borreliosis, the most common tick-born disease, is transmitted to humans by a bite from an infected tick. The most common symptoms of infection include a bull’s eye rash, fever, and muscle pain although some do not develop symptoms or fail to notice a rash.
The number of Lyme borreliosis cases and its geographical distribution is increasing. In Europe, 20-25% of ticks are infected and the risk of infection after a tick bite is 1%-5% although the actual infection rate is believed to be higher. The risk of becoming infected may be greater than 70% if the tick is engorged or remains attached for longer than 36 hours.
Lyme disease prevention involves using insect repellent, removing attached ticks promptly, and applying pesticides. No pharmaceutical prevention strategy is available. In Europe and in the USA, the oral antibiotic doxycycline is used once a skin rash develops.
Although the study was stopped prematurely, the authors conclude a preventive treatment is possible and that their experience may assist other researchers in designing studies in the prevention of Lyme borreliosis.
Written By: Lynn Kim