The anti-parasitic drug ivermectin, which has increased in popularity as an alternative Covid-19 treatment, was found to be ineffective against Covid-19, according to a study of more than 1,300 people at risk of severe Covid-19 published in the New England Journal of Medicine.

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Background

Ivermectin is an anti-parasite drug, which was first discovered in 1975. It was initially introduced as a drug for livestock in the 1980s, and a version of the drug for humans was developed later.

Ivermectin is used to treat several parasitic infections around the world, including river blindness and elephantiasis. Around 250 million people take ivermectin to treat parasitic infections every year, and its side effects, such as nausea, itching, and rashes, are typically mild.

Although ivermectin is not an anti-viral drug, many researchers at the start of the pandemic began testing existing drugs to see if they could be repurposed as treatments for Covid-19. Early on, several small studies on ivermectin suggested the drug could be effective as a treatment against Covid-19, but since then, several larger, well-conducted studies have suggested that any benefits of the drug are small or that it has no effect on patients.

Despite that, some doctors began prescribing ivermectin as a Covid-19 treatment, leading FDA to issue a warning that the drug was not approved for that use.

Study details and key findings

The NEJM study, published Wednesday, was conducted in Brazil as part of a clinical trial called TOGETHER which began in June 2020. It is the largest trial to date of the effect of ivermectin on Covid-19.

The study looked at 1,358 adults who had visited one of 12 clinics in the Minas Gerais region of Brazil with Covid-19 symptoms. The patients all tested positive for the disease and were considered at risk of severe Covid-19 because of other comorbidities, including hypertension or a history of diabetes.

Half of the patients received ivermectin while the other half received a placebo. The trial was a double-blind study, meaning neither the patient nor the health care provider knew whether the patient received ivermectin or a placebo. The patients were then followed from March 23 to Aug. 6, 2021.

The researchers tracked whether the patients were hospitalized within 28 days of receiving their treatment, as well as how effectively ivermectin cleared the coronavirus from the patients' bodies, whether the patients' symptoms resolved sooner with ivermectin, how their time in the hospital compared, and whether there was a difference in death rates.

Ultimately, the researchers found no significant differences between the two groups. The researchers also looked to see if taking ivermectin within the first three days of a positive Covid-19 test had any effect, but found that those who did actually had worse outcomes than those in the placebo group.

"There was no indication that ivermectin is clinically useful," said Edward Mills, one of the lead authors on the study and a professor of health sciences at McMaster University in Canada.

'An unpromising approach'

Experts praised the study for its size and design and said they hope it will deter doctors from prescribing ivermectin to Covid-19 patients.

"This is the first large, prospective study that should really help put to rest ivermectin and not give any credibility to the use of it for Covid-19," said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.

David Boulware, an infectious disease expert at the University of Minnesota, said the study shows "[t]here's really no sign of any benefit" in taking ivermectin. "Now that people can dive into the details and the data, hopefully that will steer the majority of doctors away from ivermectin and towards other therapies."

While there are other trials looking at the effectiveness of ivermectin in treating Covid-19, Boulware said he doubts any of them will find different results, given how well-designed the TOGETHER trial was. "Rarely would you expect to find something different," he said.

Paul Sax, an infectious disease expert at Brigham and Women's Hospital in Boston who was not involved in the TOGETHER trial, said, "I welcome the results of the other clinical trials and will view them with an open mind, but at some point it will become a waste of resources to continue studying an unpromising approach." (Zimmer, New York Times, 3/30; Toy, Wall Street Journal, 3/18; Walker, MedPage Today, 3/30)