Ivermectin

Description

Ivermectin is an antiparasitic agent effective in the treatment of onchocerciasis, or "river blindness". Since ivermectin acts to prevent the adult worm from producing microfilariae, it needs to be administered only once or twice a year.

The Uses of Ivermectin

Semi-synthetic derivative of Abamectin; consists of a mixture of not less than 80% component B1a and not more than 20% component B1b. Antihelmintic (Onchocerca)

Background

Ivermectin is a semi-synthetic antiparasitic medication derived from avermectins, a class of highly-active broad-spectrum antiparasitic agents isolated from the fermentation products of Streptomyces avermitilis. Ivermectin itself is a mixture of two avermectins, comprising roughly 90% 5-O-demethyl-22,23-dihydroavermectin A1a (22,23-dihydroavermectin B1a) and 10% 5-O-demethyl-25-de(1-methylpropyl)-22,23-dihydro--25-(1-methylethyl)avermectin A1a (22,23-dihydroavermectin B1b).
Ivermectin is mainly used in humans in the treatment of onchocerciasis, but may also be effective against other worm infestations (such as strongyloidiasis, ascariasis, trichuriasis and enterobiasis). Applied topically, it may be used in the treatment of head lice infestation.
With the advent of 2020 and the COVID-19 pandemic, ivermectin began garnering notoriety due to its off-label use for the prophylaxis and treatment of COVID-19. While studies are still ongoing, much of the evidence for ivermectin in COVID-19 relies on pre-print in vitro data, and the clinical utility of this data remains unclear. Due to a number of factors - for example, the relatively low number of patients per trial and the speed at which these trials were conducted - studies on the use of ivermectin in COVID-19 have been fraught with statistical errors and accusations of plagiarism. In addition, the use of aggregate patient data in large-scale meta-analyses (as opposed to individual patient data (IPD)) has been shown to disguise otherwise blatant data errors, such as extreme terminal digit bias and the duplication of blocks of patient records.
Until high-quality, peer-reviewed data regarding both the safety and efficacy of ivermectin for COVID-19 in humans becomes available, the use of ivermectin for these purposes should be avoided in favour of thoroughly-vetted therapies (e.g. COVID-19 vaccines like Comirnaty).

Indications

Administered topically, ivermectin cream is indicated for the treatment of inflammatory lesions associated with rosacea. An over-the-counter ivermection lotion is commercially available and indicated for the topical treatment of head lice infestations in patients ≥6 months of age.
Orally administered ivermectin is indicated as a broad-spectrum anti-parasitic for the treatment of intestinal strongyloidiasis caused by Strongyloides stercoralis and onchocerciasis caused by Onchocerca volvulus. Systemic ivermectin therapy is used internationally for the treatment of various tropical diseases, including filariasis, cutaneous larva migrans, and Loa loa infection, amongst others.

Pharmacokinetics

Ivermectin is a semisynthetic, anthelminitic agent. It is an avermectin, a group of pentacyclic sixteen-membered lactones (i.e. a macrocyclic lactone disaccharide) derived from the soil bacterium Streptomyces avermitilis. Avermectins are potent and broad-spectrum anti-parasitic agents.

Toxicity

Used appropriately, topically applied ivermectin lotions and creams are unlikely to cause significant toxicity. With accidental or intentional significant exposure to unknown quantities of veterinary formulations of ivermectin (by ingestion, inhalation, injection, or significant body surface area exposure) patients have reported rash, edema, headache, dizziness, asthenia, nausea, vomiting, and diarrhea. Other less common effects include seizure, ataxia, dyspnea, abdominal pain, paresthesia, urticaria, and contact dermatitis. Overdosage with orally administered ivermectin was lethal in mice and rats (at doses several-fold higher than the recommended dose), with death preceded by significant ataxia, bradypnea, tremors, ptosis, decreased activity, emesis, and mydriasis.
If overdosage of ivermectin is suspected, initiate supportive therapy as clinically indicated, including the use of parenteral fluids and electrolytes, respiratory support, and pressor agents to manage hypotension. Induction of emesis and/or gastric lavage may be considered alongside other purgatives and routine anti-poison measures if clinically indicated.

Absorption

Moderately well absorbed. Improved absorption with high fat meal.

Metabolism

Primarily hepatic. Ivermectin and/or its metabolites are excreted almost exclusively in the feces over an estimated 12 days, with less than 1 % of the administered dose excreted in the urine.