Effectiveness of isopropyl myristate/cyclomethicone D5 solution of removing cuticular hydrocarbons from human head lice (Pediculus humanus capitis)

BACKGROUND: In the treatment of human head lice infestation, healthcare providers are increasingly concerned about lice becoming resistant to existing pesticide treatments. Traditional pesticides, used to control these pests, have a neurological mechanism of action. This publication describes a topical solution with a non-traditional mechanism of action, based on physical disruption of the wax layer that covers the cuticle of the louse exoskeleton. This topical solution has been shown clinically to cure 82% of patients with only a 10-minute treatment time, repeated once after 7 days. All insects, including human head lice, have a wax-covered exoskeleton. This wax, composed of hydrocarbons, provides the insect with protection against water loss and is therefore critical to its survival. When the protective wax is disrupted, water loss becomes uncontrollable and irreversible, leading to dehydration and death. A specific pattern of hydrocarbons has been found in all of the head louse cuticular wax studied. Iso-octane effectively removes these hydrocarbons from human head lice’s cuticular wax. METHODS: A method of head louse cuticle wax extraction and analysis by gas chromatography was developed. Human head lice (Pediculus humanus capitis) were collected from infested patients and subjected to any of three extraction solvents comprising either the test product or one of two solvents introduced as controls. A gas chromatograph equipped with a flame ionization detector (GC/FID) was used to determine the presence of hydrocarbons in the three head lice extracts. RESULTS: In the study reported herein, the test product isopropyl myristate/cyclomethicone D5 (IPM/D5) was shown to perform comparably with iso-octane, effectively extracting the target hydrocarbons from the cuticular wax that coats the human head louse exoskeleton. CONCLUSIONS: Disruption of the integrity of the insect cuticle by removal of specific hydrocarbons found in the cuticular wax appears to offer a mechanism for killing lice without the likelihood of encountering genetic resistance.