Onchocerciasis, known as river blindness, is caused by the parasitic worm Onchocerca volvulus, transmitted by blackflies that breed in fast-flowing rivers. It is the world's second leading infectious cause of blindness. Ivermectin is the FDA-approved treatment for this disease, and the work that produced it earned Satoshi Ōmura and William C. Campbell a share of the 2015 Nobel Prize in Physiology or Medicine.
Adult female worms live in fibrous nodules under the skin and release enormous numbers of larvae called microfilariae, which migrate through skin and eye tissue. The damage of onchocerciasis — severe itching, skin changes and progressive eye damage leading to blindness — is caused by the inflammatory response to dying microfilariae, not by the adult worms directly.
Ivermectin is a potent microfilaricide. It rapidly clears microfilariae from skin and eye tissue and suppresses their release from adult females for months. It does not reliably kill the adult worms, which can live for 10 to 15 years, which is why treatment must be repeated over many years.
The standard dose is 150 micrograms per kilogram of body weight as a single oral dose, repeated every 6 to 12 months for as long as the person remains infected or at risk of reinfection. In mass drug administration campaigns, annual or semi-annual dosing is delivered community-wide.
In 1987 Merck committed to donate ivermectin — as Mectizan — for as long as needed to eliminate onchocerciasis. The Mectizan Donation Programme has since delivered billions of treatments and is generally regarded as one of the most successful public-private health partnerships ever established.
The results have been substantial. Colombia, Ecuador, Mexico and Guatemala have been verified by the WHO as free of onchocerciasis transmission. Transmission has been interrupted across large areas of West Africa. This is the single strongest body of real-world evidence for ivermectin's effectiveness in any indication.
In regions of Central Africa where Loa loa co-exists with onchocerciasis, people carrying very high Loa loa microfilarial loads can develop serious and occasionally fatal encephalopathy after ivermectin. This is a recognised risk requiring pre-treatment screening in those specific regions. It is not a general risk of ivermectin outside co-endemic areas.
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View products and pricingYes. Onchocerciasis is one of the two FDA-approved indications for oral ivermectin in humans, alongside intestinal strongyloidiasis. It is also on the WHO Model List of Essential Medicines for this use.
No. Ivermectin kills the microfilariae and suppresses their production for months, but adult Onchocerca volvulus worms survive and can live 10 to 15 years. This is why treatment is repeated every 6 to 12 months over many years rather than given once.
Satoshi Omura isolated the soil bacterium Streptomyces avermitilis and William C. Campbell developed avermectin into ivermectin. Their work transformed the treatment of onchocerciasis and lymphatic filariasis and they shared the 2015 Nobel Prize in Physiology or Medicine.