Scabies is a common skin condition caused by a tiny parasitic mite that infests the skin, leading to intense itching and a characteristic rash. Ivermectin is a widely used medication to combat these microscopic invaders. It targets specific biological pathways within the mite, leading to its demise and alleviating the symptoms of infestation.
The Scabies Mite: A Tiny Invader
The human itch mite, Sarcoptes scabiei var. hominis, causes scabies. This microscopic mite is less than half a millimeter, making it nearly invisible to the naked eye. The female mite burrows into the outermost layer of human skin, laying eggs that hatch into larvae within three to four days.
Larvae move to the skin surface, mature through nymphal stages, and become adult mites. The mites, their eggs, and waste products trigger an allergic reaction, causing severe itching, often worse at night. Characteristic signs include a pimple-like rash and tiny, raised, wavy lines indicating burrows.
Ivermectin’s Action: Targeting the Mite’s Nerves
Ivermectin, a medication derived from macrocyclic lactones, interferes with the nervous system of invertebrates like the scabies mite. It binds to specific proteins called glutamate-gated chloride channels (GluCls) on the mites’ nerve and muscle cells.
Once ivermectin binds to GluCls, it causes the channels to open. This leads to a sustained influx of chloride ions into the mite’s nerve and muscle cells. The increased concentration of negatively charged chloride ions inside the cells results in hyperpolarization, making the cell membrane more negative and less excitable. This disrupts the normal electrical signals necessary for nerve and muscle function.
Ivermectin’s safety for humans stems from its selective toxicity. While GluCls are prevalent and crucial for survival in invertebrates, they are largely absent or not significantly present in the mammalian central nervous system. Even if some binding occurs, the drug does not typically cross the blood-brain barrier in amounts that cause significant effects.
Paralysis and Elimination: The Outcome
Ivermectin’s disruption of nerve and muscle function leads to flaccid paralysis in scabies mites. In this paralyzed state, the mites lose their ability to move, feed, and burrow through the skin. They become immobilized.
This incapacitation prevents the mites from carrying out essential life functions. Unable to feed, the mites will eventually die from starvation or dehydration. The dying mites are then gradually eliminated from the host’s skin. Ivermectin is not effective against mite eggs, necessitating a second dose to target newly hatched mites.
Ivermectin Use and Safety Considerations
Ivermectin is typically administered orally as a tablet for scabies treatment. The usual dosage is 200 micrograms per kilogram of body weight, often given in two doses spaced seven to fourteen days apart. This two-dose regimen helps ensure that any mites that hatch from eggs after the first dose are also eliminated.
While generally well-tolerated, safety considerations exist. It is not recommended for pregnant or breastfeeding individuals, as its safety has not been fully established. It is also avoided in children weighing less than 15 kilograms. Medical supervision is needed to determine appropriate dosage and monitor for adverse effects.