Scabies – infestation with the mite Sarcoptes scabiei – is most commonly treated with topical permethrin or oral ivermectin. For most scabies cases, ivermectin is used in a two dose regimen: a first dose kills the active mites, but not their eggs. Over the next week, the eggs hatch, and a second dose kills the newly hatched mites. For severe "crusted scabies", the U.S. Centers for Disease Control and Prevention (CDC) recommends up to seven doses of ivermectin over the course of a month, along with a topical antiparasitic. Both head lice and pubic lice can be treated with oral ivermectin, an ivermectin lotion applied directly to the affected area, or various other insecticides. Ivermectin is also used to treat rosacea and blepharitis, both of which can be caused or exacerbated by Demodex folliculorum mites. Contraindications
The only absolute contraindication to the use of ivermectin is hypersensitivity to the active ingredient or any component of the formulation. In children under the age of five or those who weigh less than 15 kilograms (33 pounds), there is limited data regarding the efficacy or safety of ivermectin, though the available data demonstrate few adverse effects. However, the American Academy of Pediatrics cautions against use of ivermectin in such patients, as the blood-brain barrier is less developed, and thus there may be an increased risk of particular CNS side effects such as encephalopathy, ataxia, coma, or death. Such patients should be monitored very closely when given ivermectin.
Use in turtles is particularly contraindicated.A characteristic of the antinematodal action of ivermectin is its potency: for instance, to combat Dirofilaria immitis in dogs, ivermectin is effective at 0.001 milligram per kilogram of body weight when administered orally.For dogs, the insecticide spinosad may have the effect of increasing the toxicity of ivermectin. Pharmacology
Mechanism of action
Ivermectin and its related drugs act by interfering with the nerve and muscle functions of helminths and insects. The drug binds to glutamate-gated chloride channels common to invertebrate nerve and muscle cells. The binding pushes the channels open, which increases the flow of chloride ions and hyper-polarizes the cell membranes, paralyzing and killing the invertebrate. Ivermectin is safe for mammals (at the normal therapeutic doses used to cure parasite infections) because mammalian glutamate-gated chloride channels only occur in the brain and spinal cord: the causative avermectins usually do not cross the blood–brain barrier, and are unlikely to bind to other mammalian ligand-gated channels. Pharmacokinetics
Ivermectin can be given by mouth, topically, or via injection. It does not readily cross the blood–brain barrier of mammals due to the presence of P-glycoprotein (the MDR1 gene mutation affects the function of this protein). Crossing may still become significant if ivermectin is given at high doses, in which case brain levels peak 2–5 hours after administration. In contrast to mammals, ivermectin can cross the blood–brain barrier in tortoises, often with fatal consequences. Chemistry
Fermentation of Streptomyces avermitilis yields eight closely related avermectin homologues, of which B1a and B1b form the bulk of the products isolated.