Anti-mite and louse medications

Definitions & Key takeaways

Anti-mite and louse medications are medications that are used to kill or get rid of mites and lice. Mites and lice can cause skin irritation, itching, and other problems. There are different anti-mite and louse medications available, including over-the-counter medications as well as prescription medications.

Some common anti-mite and louse medications include permethrin, malathion, benzyl alcohol, pyrethrins, and piperonyl butoxide. All permethrin, malathion, and benzyl alcohol are used to treat head lice. In addition to treating head lice, malathion is also used to treat scabies, and benzyl alcohol to treat pubic lice. Pyrethrins are a natural insecticide that is derived from chrysanthemums. Piperonyl butoxide is a common ingredient in lice treatments that helps to increase the effectiveness of the pyrethrins.

Chapters:

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Introduction0:00–0:27

Mites and lice are arthropod ectoparasites, (or external parasites), that live on the surface of the body, like the skin or hair.
Ectoparasiticides are topical medications used to treat these infestations. Endectocides on the other hand, are multi-purpose antiparasitics that work on both external parasites and some internal parasites, like roundworms.

Pathology0:27–1:53

Now, lice are wingless insects that live off of the blood of their hosts. There are 3 types of lice that infest humans: head louse that lives in the hair of the scalp; body louse that lives in the hair of the axilla, back, and pubic region; and pubic louse, also called crab louse, that lives in pubic and axillary hair, but also the eyebrows.
Lice infestation is called pediculosis and the main symptom is pruritus, (or itchiness), which is caused by an allergic reaction to louse’s saliva.
Scratching of the bites could also lead to bacterial skin infections. Another common ectoparasite is the Sarcoptes scabiei mite which cause scabies.
These tiny critters are eight-legged arthropods that are related to spiders. Unlike spiders, scabies mites burrow into the skin and cause a pimple like rash locally.
Even worse, they tunnel around under the skin, forming elevated tracks that are visible on the skin surface. The burrowing causes intense itching that’s more frequent at night when the mites are more active.
The most common sites for scabies are between the fingers, on the flexor surface of the wrist, and the extensor surface of the elbow and knees.
They can also be found around the areola of the breast and the pubic region. Permethrin is an ectoparasiticide and an insecticide.

Permethrin1:53–3:04

It’s the first line medication for both scabies and pediculosis. This medication is used topically in the forms of creams, lotions, or shampoos.
Once taken in by the parasite, permethrin binds to sodium channels on the membrane of neurons, and prolongs their inactive state.
This results in delayed repolarization, leading to respiratory muscle paralysis and death. One benefit of permethrin is that it’s ovicidal, meaning it also kills the eggs of lice and mites.
This medication is slowly absorbed into the skin and has a residual effect even after it’s rinsed off. Another advantage of this medication is the relatively mild profile of its side effects, like local skin irritation and burning sensation.
It’s generally considered safe to use with younger children and during pregnancy. One down side for pet owners is that even a small dose is extremely toxic for felines, so it’s not a good idea to handle cats or kittens while using permethrin.

Lindane3:04–4:15

Another topical ectoparasiticide is lindane, which is an organochlorine that was formerly used as an insecticide until it was banned.
It’s less effective than permethrin for treating scabies and pediculosis, and it has more side effects as well, so it’s only used as a second line medication.
Lindane exerts its parasiticidal effect by binding to receptors for GABA, the chief inhibitory neurotransmitter. This result in hyperexcitable neurons that fire spontaneously, causing muscle spasm and the eventual death of the parasite.
Lindane is also effective at killing the eggs of mites and lice. When absorbed through the skin, it can act as a CNS stimulant, causing side effects like paresthesia and seizures.
Less severe side effects include rashes, itching, and headaches. It’s considered unsafe for use during pregnancy, and is not recommended for children and the elderly.
In most countries, lindane is outright banned as it is a potential human carcinogen, and its usage should be minimised elsewhere.

Crotamiton4:15–4:41

Crotamiton is another topical ectoparasiticide. The mechanism behind its parasiticidal effects is unknown, but it does block the effect of histamine, which helps reduce itchiness.
It’s mainly used against scabies, so the antipruritic effects are quite beneficial. It’s main side effect is mild skin irritation so it’s preferred over lindane.

Ivermectin4:41–5:35

Ivermectin is an endectocide that’s able to kill external and internal parasites. It’s mainly used perorally against roundworm infections, but both peroral and topical forms of the medication are effective against lice and mite infestations.
Ivermectin kills by interfering with the nervous system of invertebrates, by binding to invertebrate-specific glutamate gated chloride channels, on neurons and muscle cells.
This causes them to open permanently, leading to a rapid influx of chloride ions. This hyperpolarizes the cells, which leads to muscle paralysis and death.
It has little effect on humans, but any side effects of ivermectin are mild and include headaches, dizziness, muscle pains, and GI problems like nausea and diarrhea.
So, let’s make a mnemonic to help you memorize and retain all these crazy pharm facts! Let’s go back in time to the last ice age where giant lice and mites roam the earth.

Memory Palace5:35–7:05

For the ectoparasiticides, a patch of the ground is frozen in a permafrost, for permethrin. There’s a hole in the permafrost that’s actually a lion’s den for lindane.
Hunting the lion, is a type of early human called Cro-Magnon, for crotamiton. The Cro-Magnon is scratching his buttocks to help you remember crotamiton is also an antipruritic.
The most important side effect to remember is that lindane is a CNS stimulant and could cause seizures, so let’s give the lion a can of energy drink.
A little kid and his pregnant mother is fleeing from the lion to help you remember it’s not safe for use during pregnancy and younger children.
Off to the other side is the endectocide ivermectin, represented by a mammoth with big ivory tusks. It’s eating a giant prehistoric roundworm to help you remember it’s also effective against internal parasites.
For side effects, the mammoth was in a fight and there’s a spear sticking out of his leg for muscle pain, and he’s got a lump on his head for headaches.
There’s a pile of vomit next to him to help you remember the gastrointestinal side effects. All right, as a quick recap.

Review7:05–7:45

Anti-mite and louse medications can be ectoparasiticides like permethrin, lindane, and crotamiton, or endectocides like ivermectin.
These medications often target the nervous system of these parasites. Ectoparasiticides are for topical use only and generally have few side effects related to skin irritation.
Lindane is the exception, since it’s a CNS stimulant that could cause seizures. Endectocides like ivermectin come in oral and topical forms and they can also treat internal parasites like roundworms.

Mind Map7:45–7:58

But wait, there's more: Here's a mind map with all of the mnemonics from the video. Go ahead and pause the video so you can test yourself to see what you remember.
Stay tuned for the answers at the end.