Drug Resistance Issues

Resistance of head lice to insecticide treatments derived from pyrethroids such as permethrin is a major global health issue that leads to treatment failure. Pyrethroids are used in many common head lice treatments. Up until 1994, reports showed that commercially available insecticides such as permethrin were 94% to 100% effective. Recent reports show only a 28% to 55% efficacy when patients were treated with permethrin, even in conjunction with proper combing. Such development suggests that the prevalence of resistance has, and still is, rapidly increasing across North America.1

Below is a map of resistant allele frequencies in head lice sampled in 12 major cities in Ontario. With the exception of Sudbury, Oakville and Central Toronto, resistant alleles occurred in 100% of sampled lice.2

Resultz® head lice treatment does not use pyrethroids. 

How is Resultz®Different?


  1. Yoon KS, Previte DJ, Hodgdon HE, Poole BC, Kwon DH, El-Ghar GEA, et al. Knockdown resistance allele frequencies in North American head louse (Anoplura: Pediculidae) populations. J Med Entomol. 2014;51(2):450–7.
  2. Marcoux D, Palma KG, Kaul N, Hodgdon H, Van Geest A, Previte DJ, et al. Pyrethroid Pediculicide Resistance of Head Lice in Canada Evaluated by Serial Invasive Signal Amplification Reaction. J Cutan Med Surg. 2010;14(3):115–8.