Study: 98% of Head Lice in at Least 42 States Now Resistant to Common OTC Treatments
Fully 98 percent of head lice in at least 42 states are resistant to various over-the-counter pyrethrins and pyrethroids including permethrin, which is the active ingredient in popular treatment formulations for pediculosis (Nix® (permethrin 1%), according to a study in the Journal of Medical Entomology.
The research was published in March 2016, and is now being highlighted by ParaPRO, a specialty pharmaceutical company developing new antiparasitic formulations.
The study was designed to determine the extent and magnitude of the knock-down resistance (kdr)-type mutations responsible for the increasing prevalence of head lice resistant to common treatment formulations. Between July 22, 2013 and May 11, 2015, lice were collected from 138 collection sites in 48 U.S. states and analyzed by quantitative sequencing. Previously published data were used to compare changes in the frequency of the kdr-type mutations over time. The overall mean percent resistance allele frequency (mean % RAF) (+/-SD) for all analyzed lice was 98.3 +/- 10%.
Forty-two states (88 percent) had a mean % RAF of 100%, the study showed. The frequencies of kdr-type mutations did not differ regardless of the human population size. The study correlated the loss of efficacy of the Nix® formulation (Prestige Brand, Tarrytown, NY) from 1998 to 2013 to the increase in kdr-type mutations. The results demonstrated a parallel increase of kdr-type mutations in lice over time, which provide a plausible reason for the decrease in the effectiveness of permethrin in Nix®.
Specifically, the percent of lice-free patients following treatment by the OTC Nix formulation was essentially 100 percent from 1986 to 1998, but from 1998, the overall effectiveness of the Nix formulation steadily declined and was only 25 percent effective by 2009, a 75 percent decline in overall effectiveness in clinical trials over 10 years, the study showed.
"This newly published data supports what we've been seeing in our offices and clinics: an increase in treatment-resistant super lice," says Chris Belcher, M.D., a pediatric infectious disease specialist at the Peyton Manning Children's Hospital at St. Vincent, Indianapolis, IN, in a news release. "It's important that parents contact a clinician if they suspect their child has head lice. There are effective, non-pyrethrin, non-pyrethroid-based prescription agents that can be used if treatment with over-the-counter products such as Nix® has been unsuccessful."