Ivermectin, a controversial antiparasitic drug that has been touted as a potential treatment for Covid-19, does not accelerate recovery in people with mild cases of the disease, according to a randomized clinical trial published Thursday in the journal JAMA.
Ivermectin is commonly used to treat parasitic worms in people and animals, but scientific evidence for its effectiveness against coronavirus is scarce. Some studies have indicated that the drug can prevent several different viruses from replicating in cells. And last year, researchers in Australia found that high doses of ivermectin suppressed SARS-CoV-2, the virus that causes Covid-19, in cell cultures.
These discoveries spurred the use of the drug against Covid-19, especially in Latin America.
“Ivermectin is being used widely today,” said Dr. Eduardo López-Medina, a doctor and researcher at the Pediatric Infectious Diseases Center in Cali, Colombia, who led the new trial. “In many countries in the Americas and in other parts of the world, it is part of Covid’s national treatment guidelines.”
But the drug also proved to cause division. While some scientists see potential, others suspect that effective coronavirus inhibition may require extremely high and potentially dangerous doses. Health officials also fear that people desperate for coronavirus treatments could take versions of the drug formulated for pets. (It is commonly used to prevent heartworm in dogs.)
“There are many conflicting views on this, sometimes extremely conflicting views,” said Dr. Carlos Chaccour, a researcher at the Barcelona Institute of Global Health who was not involved in the new study. “I think it has become another hydroxychloroquine.”
But neither the proponents nor the critics had much rigorous data to support their views. There are few well-controlled studies on the effectiveness of the drug against Covid-19, although more are expected in the coming months. And the National Institutes of Health treatment guidelines note that there is insufficient evidence “to recommend for or against” the use of the drug in patients with Covid-19.
In the new study, Dr. López-Medina and his colleagues randomly assigned more than 400 people who recently developed mild Covid-19 symptoms to receive a five-day course of ivermectin or placebo. They found that the symptoms of Covid-19 lasted about 10 days, on average, among people who received the drug, compared with 12 days among those who received the placebo, a statistically insignificant difference.
The new study adds much-needed clinical data to the debate over the use of the drug to treat Covid-19, said Dr. Regina Rabinovich, a global health researcher at Harvard’s School of Public Health TH Chan, who was not involved in the study.
But she noted that the study was relatively small and did not answer the most urgent clinical question, whether ivermectin can prevent serious illness or death. “The duration of symptoms may not be the most important clinical or public health parameter to watch for,” she said.
The researchers found that seven patients in the placebo group worsened after enrolling in the study, compared with four in the ivermectin group, but the numbers were too small to draw a significant conclusion.
“There was a small sign there, and it would be interesting to see if that sign that we saw is real or not,” said Dr. López-Medina. “But that would have to be answered in a larger trial.”
Dr. López-Medina also pointed out that the study population was relatively young and healthy, with an average age of 37 years and few of the underlying conditions that can make Covid-19 more dangerous.
Larger trials, which are currently underway, may provide more definitive answers, said Dr. Rabinovich, who noted that she was “totally neutral” as to the potential usefulness of ivermectin. “I only want data because there is huge chaos in the field.”