Ivermectin sold under brand names Stromectol® in the US and Mectizan® in Canada. It is a anti-parasite medication and is effective against most common intestinal worms (except tapeworms), most mites, and some lice. While normally used to treat animals it is also prescribed to humans to treat infections of strongyloides stercoralis and onchocerciasis (river blindness).
Ivermectin is chemically related to the insecticide avermectin, the active ingredient in some home-use ant baits. Both ivermectin and avermectin are derived from the bacterium Streptomyces avermitilis and kill by interfering with the target animal's nervous system.
In General Use Pesticide (GUP) formulations, these compounds are classified as EPA toxicity category IV, or very low. This means that although highly poisonous to insects, mammals should not generally be adversely affected by normal use of avermectin pesticide formulations. As an example, one such formulation was determined to have an oral LD50 (semi-lethal dose) of 650 mg/kg in rats (qualifies as toxicity category III--low toxicity). Extrapolated to a 180-pound human, this semi-lethal dose is almost 2 ounces, or an amount of the pesticide equal to about four dominoes, which is considered by the EPA to be a low toxicity amount.
However, pure avermectin formulations are both highly toxic to insects and mammals (as well as aquatic life, such as fish). One study reports an oral LD50 of 10 mg/kg in rats (qualifies as toxicity category I--high toxicity).
Indications for Human Use
Ivermectin is a broad-spectrum antiparasitic agent. It is mainly used in humans in the treatment of onchocerciasis, but is also effective against other worm infestations (such as strongyloidiasis, ascariasis, trichuriasis and enterobiasis). More recent evidence supports its off-label use in the treatment of mites such as scabies, usually limited to cases that prove resistant to topical treatments and/or who present in advanced state (such as Norwegian scabies).
Oral: 3 to 12 mg as a single dose per os (about 150 to 200 µg/kg bodyweight) for onchocerciasis and other parasitic infections. (Ex. 45 kg would be about 6.75 mg to 9 mg)
Ivermectin is not given to children weighing less than 15 kg. The dose is 150 µg/kg bodyweight (in children weighing more).
Ivermectin is contraindicated in persons with an immediate hypersensitivity to the drug. It should not be given to mothers who are breast-feeding until the infant is at least three months old (Reynolds, 1993).