Lately there has been quite a heated controversy about whether to use ivermectin for Covid-19. The FDA, a US federal agency responsible for providing unbiased information to protect people from harmful drugs, foods, even tobacco products, has said that there is not good evidence of ivermectin's safety and effectiveness in treating Covid 19, and that just about sums up what we truly know about ivermectin in the context of Covid. The CDC, Centers for Disease Control, a branch of the department of Health and Human Services, tasked with preventing and treating disease and injury, also recently warned people not to use ivermectin to treat Covid outside of actual clinical trials.
Certain highly qualified physicians, including ones who practice critical care medicine and manage many patients with severe Covid infections in the intensive care unit vocally support the use of ivermectin to treat Covid and have published dosing schedules and reviews of the literature supporting it for treatment of early infection, also to prevent infection and to treat "long Covid" which is the distressing aftermath of infection.
Many articles have come out, in medical journals, also in highly regarded popular sources such as the NY Times and Wall Street Journal, primarily either discouraging the use of ivermectin for Covid 19 or deriding people who would prescribe or seek out such treatment.
What is going on?
Ivermectin is one of several antiparasitic medications derived from a soil bacterium which have been game changing for treating both animals and people. William Campbell and Satoshi Omura won the Nobel Prize in 2015 for developing the parent drug, Avermectin, from which ivermectin was derived. Ivermectin shows promise in eliminating two horrendous tropical diseases, River Blindness and Lymphatic Filariasis (previously known as elephantiasis due to the disfiguring swelling it causes.) As it has gotten more available and less expensive, it has become one of my go-to medications for severe cases of scabies, a tiny mite that lives on the skin and causes itching and often bacterial infection. It works extremely well. Ivermectin, in doses used to treat parasitic diseases, is very safe and low in side effects. So in this mystery of why ivermectin has become such a controversial subject, we have two main questions. What is our evidence that it works and what is the harm of using it?
The Evidence that it Works: It is very easy to convince ourselves that a drug works when it does not, if we don't do really good studies. There have been many drugs that have appeared to work for Covid which have not actually helped or, indeed, were shown to cause harm when we gathered enough high quality data. There are many sources of bias that can lead to this sort of thing. Let's take, for example, chocolate ice cream. Say we have a community that is ravaged by Covid and we introduce chocolate ice cream therapy. We may find that patients who eat chocolate ice cream do, in fact, recover from Covid faster than ones who do not. It could be the ice cream or it could be the fact that people who want to eat ice cream are starting to feel better or that we are just getting better at treating Covid by the time we start our chocolate ice cream study. It could be related to other characteristics of patients who like chocolate ice cream. Lactose intolerance is more common in people of color who have also been noted to have higher mortality rates from Covid. Biases can enter into studies in very subtle ways or in ways that are not subtle at all. Ivermectin can kill Covid viruses in the laboratory, but so can other drugs which have proved not to be effective. Whole areas of the world have started to use ivermectin as a treatment for Covid, primarily in the developing world. Physicians who back ivermectin as treatment note that in those communities after ivermectin is introduced, death rates start to fall. But we have all noticed that when Covid death rates get really high, they eventually start to fall anyway. It's the nature of the disease and the nature of people, who use many mitigating strategies when the epidemic heats up, including things like masking and lock downs.
What is the harm?
I have mentioned that ivermectin is pretty safe. It is, at standard doses. The most responsible of the doctors who recommend ivermectin recommend pretty standard doses, but ivermectin is available in veterinary formulations and is really inexpensive, so people are just buying it online or from local feed stores and taking it. When they take it in veterinary doses, and many will because there are no instructions for human use, they can be poisoned. I just looked online for "horse paste"--one veterinary option, and found that a little tube of horse dewormer weighing a small fraction of an ounce, had 10 standard human doses in it. It is not obvious to a regular person that a tube is too much and next to impossible to figure out how to squeeze out a tenth of a tube for each dose. Plus it was very unclear what the other ingredients in the paste were, since only about 1/50th of it was ivermectin.
So why don't we just prescribe human ivermectin in safe doses to all of our patients who might request it, or if we believe the very low quality data available so far, to all patients who have or might have Covid? It would certainly be safer. The reason is that doctors are supposed to be prescribing medicine based on good evidence that it works. So far we do not have good evidence that ivermectin works.
Another harm is in the overly enthusiastic promotion of ivermectin by these respectable doctors, describing patients who say that it saved their lives, making people think that they don't really need to get vaccinated, because there is always ivermectin which will cure them. Vaccination definitely can prevent Covid infection and reduce its severity in vaccinated patients who are infected. This is supported by really good unbiased studies. Encouraging patients to believe that they can safely forgo vaccination will prolong the pandemic. The experts who believe in ivermectin's effectiveness also imply that the CDC and FDA and doctors who trust them are either lying or dimwitted which is very misleading and can cause patients to mistrust their doctors or doctors to mistrust each other. That bad feeling is made worse by the other side when they call ivermectin a "horse dewormer" which, though partially true, obscures the fact that it is safe and effective for several human diseases.
But does ivermectin work to treat or prevent Covid 19? We don't know. Studies done so far have been plagued by biases (see this Cochrane Collaboration article, summarizing the data.)There are good studies in process right now. The placebo effect is powerful, and though I love a good placebo, it slows progress toward effective therapies if people are sure that they have a useful drug already. Ivermectin may prove to be helpful in treating Covid, but we really don't know yet and the road to a Covid cure is already littered with drugs we thought worked but did not.
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