Efficacy and safety of a modified combination regimen of phenothrin and ivermectin lotion in patients with head lice in Tsukuba, Japan

Abstract

AbstractObjectivesThe combination therapy of phenothrin (PHT) and ivermectin (PI regimen) was effective for pyrethroid‐resistant head lice in Okinawa; however, further investigations have been required to improve the regimen. This study aimed to investigate the efficacy of the modified PI (mPI) regimen, which increased the maximum number of PHT treatments in the PI regimen by one, in Tsukuba, which has a low mutation rate compared to Okinawa.MethodsAn open‐label, uncontrolled, exploratory study was conducted at the Department of Dermatology, University of Tsukuba Hospital to investigate the treatment effect of mPI regimen. Genotypes were investigated for the knockdown (kdr) mutations at voltage‐sensitive sodium channel (VSSC) and glutamate‐gated chloride receptor‐encoding loci to identify their correlation with drug resistance.ResultsAll the 8 patients treated with the mPI regimen resulted in lice free on day 29. Compared to baseline, the number of bodies, eggs, and itching grade significantly decreased on day 29. Mild erythema appeared after the second application of PHT on day 8 in one patient, persisted for 2 days, and recovered on day 15. No other adverse events were reported. Mutation rates were more than double in head lice collected from one patient for whom PHT was ineffective compared to those in lice from patients who responded to PHT. Furthermore, we identified four new haplotypes of VSSC loci in head lice.ConclusionsThe mPI regimen is a potential effective treatment for economically combating both PHT‐sensitive and resistant head lice.