Ivermectin may get another chance
AS THE search continues for treatments for Covid-19, the results from a number of studies have led to changes in the advice on which drugs to give people suffering from the disease.
The European Medicines Agency and the US National Institutes of Health recently stated that one previously promising treatment – the antiparasitic drug, ivermectin – is not recommended for use in routine management of Covid-19. Despite these decisions, support for ivermectin has been circulating on social media.
So what is ivermectin, and why have national agencies ruled against it?
What is ivermectin?
Ivermectin was first developed in the 1970s from a bacterium in a soil sample collected from woods alongside a Japanese golf course.
In the intervening years, the effectiveness of ivermectin and its derivatives in treating parasitic worm infections transformed human and veterinary medicine, leading to a Nobel Prize for its discoverers, William C Campbell and Satoshi Ömura.
In humans, ivermectin is prescribed in tablet form to treat certain roundworm infections that cause illnesses such as river blindness. It may also be applied as a cream to control the common inflammatory skin condition, papulopustular rosacea.
As ivermectin is more extensively used in veterinary than human medicine, however, the US Food and Drug Administration found it necessary to issue a warning in April last year against use of veterinary preparations in human patients with Covid-19.
Why might it be used to treat Covid-19?
How did a drug mainly used to treat intestinal parasites in cows come to be of interest to doctors treating humans with Covid-19?
Early last year, a paper was made public (before it was reviewed by other scientists), which showed that ivermectin suppresses the replication of the Sars-CoV-2 virus, which causes Covid-19, under laboratory conditions.
There appear to be two key ways in which the drug could prevent coronavirus replication. First, it could prevent the virus from suppressing our cells’ natural antiviral responses. Second, it’s possible the drug prevents the spike protein on the surface of the virus from binding to the receptors that allow it to enter our cells.
Why is it controversial?
Late last year, a research group in India was able to summarise the results of four small studies of ivermectin as an add-on treatment in Covid-19 patients. This review showed a statistically significant improvement in survival among patients who received ivermectin in addition to other treatments. But the authors stated clearly that the quality of the evidence was low and that the findings should be treated with caution.
A controversy then blew up over an article by the Front Line Covid-19 Critical Care Alliance, a group of doctors and researchers that lobbies for the use of ivermectin. This article, summarising multiple small studies of the effects of ivermectin on Covid-19 patients, was provisionally accepted for publication in the journal Frontiers in Pharmacology in January this year, but then rejected and removed from the journal’s website in March because of weak evidence.
One larger randomised clinical trial was published in March. This showed no effect of ivermectin on duration of symptoms of adults with mild Covid-19.
Why isn’t it recommended?
While some other studies did appear to show benefits of ivermectin, many did not. Both the National Institutes of Health and the European Medicines Agency judged, on the basis of these studies, that there is insufficient evidence to support the use of ivermectin in treatment of Covid-19.
However, more studies are under way.