Stronger is Better to Kill Lice

Ivermectin lice treatment works better in higher concentrations

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) When it comes to lice medicine, applying more doesn't mean it will work better. But stronger doses of a particular lice-killing lotion may reap benefits over weaker dosages.

According to a recently published study, the higher concentrations of the lice-killing medicine ivermectin may kill more infestations. 

And since even weaker doses can still kill the head bugs, researchers said the lotion showed promise as an effective and safe treatment for itchy heads and lice infestations.

"Ask a pharmacist about ivermectin lotion."

Terri Meinking, PhD, from the Global Health Association of Miami, Inc., and colleagues tested how well different dose concentrations of ivermectin lotion (marketed as Stromectol) worked in getting rid of head lice.

The study included 78 people between 2 and 62 years of age with head lice. The individuals were divided into one of four groups that received a single dose of lice medication containing 0.15, 0.25 or 0.5 percent ivermectin, or none of the medication at all.

Lice treatments that were considered a success resulted in no live lice after the second day.

Researchers found that all ivermectin concentrations got rid of head lice through day 15, compared to those that received a fake lotion medication without the ivermectin.

Itching also decreased across all groups by six hours after treatment and continued to decrease through day 15. The group that received the highest concentration of ivermectin itched the least. 

In addition, the group given the highest concentration also had the most lice-free participants (74 percent) by day 15.

When treatments failed, participants were given an alternate medication to kill any remaining lice.

Though lice eggs take an average of eight to nine days to hatch, the application of ivermectin continued to work to eliminate the head bugs.

"The single-treatment efficacy we report demonstrates the potential for this topical formulation of ivermectin to match the optimal levels of efficacy, safety, and convenience required in a drug used to treat head lice…," the researchers wrote in their report.

"In this dose selection study, the formulation containing 0.5 percent ivermectin provided the greatest reduction in head lice infestation, indicating that it is the appropriate concentration to enter into a Phase II development program for the purposes of providing a safe and effective alternative treatment for head lice infestation.

All three groups tolerated the different ivermectin concentrations and none experienced any eye irritation. 

Topaz Pharmaceuticals funded the study, which was published in the January 2013 issue of the International Journal of Dermatology. One of the authors was a consultant for Topaz, Taro Pharmaceutical Industries Ltd., and BioSafe Technologies, Inc. No other conflicts of interest were reported.

Reviewed by: 
Review Date: 
February 23, 2013
Last Updated:
December 31, 2013