The study reported here was conducted to investigate the mechanism of action of IPM/D5, focusing on the potential role of IPM/D5 in physically disrupting the integrity of the head louse body's outermost protection against dehydration. The cuticular wax that covers the exoskeleton of insects is vital in protecting them against dehydration and death. The wax layer of the epicuticle (outer layer) is composed of a matrix of hydrocarbons, and four specific hydrocarbons identified to be consistent among head lice by Scherer were selected for study in this work.
Isopropyl myristate/decamethylcyclopentasiloxane (IPM/D5) is a colorless, odorless solution. It was theorized that the mechanism of action for this solution involved disruption of the protective waxy coating covering the louse exoskeleton, leading to uncontrollable dehydration, and death.
It is known that suffocation of head lice is a slow process and can take up to 8 hours or more. Isopropyl myristate/cyclomethicone D5 has been shown clinically to have an 82% cure rate after two 10-minute treatments (one week apart) and therefore, suffocation is not a likely mechanism of action.
In this study gas chromatography was used to compare the hydrocarbon extraction efficiency of isopropyl myristate/cyclomethicone D5 with that of iso-octane as a control reference. Hydrocarbons specific to the waxy layer of the epicuticle of head lice were evaluated. This study showed that isopropyl myristate/cyclomethicone D5 effectively extracted the target hydrocarbons. Therefore, we deduce that the fast acting mechanism of action seen with IPM/D5 is via epicuticular hydrocarbon extraction, resulting in disruption of the waxy layer of the cuticle, followed by rapid water loss and death by dehydration.
These data support why a treatment with a physical mode of action, such as isopropyl myristate/cyclomethicone D5, can be comparable to a traditional pesticide. Pesticides, however, as evidenced in recent clinical trials, are increasingly facing issues of resistance globally. Burgess reported from a UK clinical study investigating IPM/D5 vs. 1% permethrin that IPM/D5 had 82% cure rate whereas the permethrin had only a 19% cure rate. The development of resistance to pesticides such as permethrin is well documented.
BMC Dermatol. 2012;12(15) © 2012 BioMed Central, Ltd.