Ivermectin

The treatment for onchocerciasis is ivermectin (brand name Mectizan®). Unlike previous treatments, which had serious – sometimes fatal – side effects, ivermectin is safe and can be used on a wide scale. It is also a very effective treatment, and has single-handedly transformed the lives of millions of people suffering from onchocerciasis since its introduction in 1987.

WHO/TDR/Crump A bottle of ivermectin (Mectizan®) tablets to treat onchocerciasis

Mode of action

Ivermectin kills the larval Onchocerca volvulus worms – microfilariae – that live in the subcutaneous tissue of an infected person. It is believed to paralyse or kill the microfilariae gradually, so avoiding the intense inflammatory responses induced when they die naturally. Treatment with ivermectin relieves intense skin itching and halts the progression towards blindness.

Ivermectin does not kill the adult worms but suppresses the production of microfilariae by adult female worms for a few months following treatment, so reduces transmission. As the adult worms can continue to produce microfilariae until they die naturally, ivermectin has to be taken once a year for 16–18 years to break transmission. In APOC countries, it is estimated that 65% of the total population living in an endemic area need to take ivermectin annually to eliminate onchocerciasis as a public health problem.

Dosage

Ivermectin is taken orally as tablets. A single dose of 150 to 200 µg/kg body weight needs to be taken annually to be effective. The dosage depends on a person’s body mass, which can be simply calculated according to height.

Availability

In 1987, the manufacturer of ivermectin – Merck & Co., Inc. – declared that it would donate ivermectin free of charge for as long as is needed. This unprecedented donation is administered through the Mectizan Donation Program, which works with ministries of health and other partners to distribute the drug.

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