A Cross-Species “Wonder Drug”

Each December 10, the Nobel Prizes are presented at a ceremony to honor the year’s new Laureates. When two of those, William C. Campbell and Satoshi Ōmura, were announced for the 2015 Nobel Prize in Physiology or Medicine, the animal health sector let out a collective cheer! The two scientists were recognized for their discovery and development of ivermectin, a powerful parasiticide. Through a humanitarian, free-drug program, the medicine has nearly eradicated two devastating parasitic diseases that afflict millions of people in developing countries.

So why the big cheer from animal health? Because ivermectin was in fact first developed for veterinary use and has a decades-long record of success against a myriad of serious animal parasites. It’s one of a select few drugs that can truly be described as a game changer in both veterinary medicine and the business of animal health. Let’s have a look at what makes ivermectin (and its class of related drugs) so special—and why it’s been revolutionary for the industry.

A Broad-Spectrum Weapon against Multiple Enemies

The parasites that afflict pets and production animals are numerous, from larvae and worms within the intestinal tract or circulatory system, to insects, mites, and other arthropods that live on or burrow in the skin. Whether inside or out, they can cause serious disease that sickens or even kills the host animal, and can wreak havoc on the health and productivity of farmed animals.

Before ivermectin, most parasiticides were effective against only a limited spectrum of parasites, requiring veterinarians and animal owners to deal with multiple drugs and with complicated regimens of administration. All this changed with the introduction of ivermectin, which boasts an extraordinarily broad spectrum of efficacy: simply put, it was a single drug that could kill many, many different pests.

As a result, it became possible to treat a wide variety of parasites with a single product, simplifying treatment regimens and reducing stress on the animals. With some parasites, ivermectin even proved effective against multiple life stages—such as both adult worms and their developing larvae—making it a valuable weapon in breaking the cycle of parasitic infestation.

Perhaps even more extraordinary was ivermectin’s equally high levels of efficacy against both endoparasites—those that live inside the host animal’s body—and ectoparasites—those that live outside on the skin. As a result, the introduction of ivermectin led to the coining of an entirely new scientific word: endectocide, a product that fights both internal and external parasites. 

The discovery of ivermectin, and its application in veterinary medicine, truly revolutionized parasite control in all major domestic animal species.”

Mark Soll, Merial Global Head of Clinical Research & Development

Systemic Action for Wider Control

Another big breakthrough with ivermectin was its systemic nature: whether administered orally, topically, or by injection, it can reach parasites throughout the body. In contrast, many prior anti-parasitic drugs had to be applied topically to kill parasites on the skin, or administered orally in order to kill worms in the intestinal tract. Ivermectin’s systemic activity made it much easier to target multiple parasites in different locations—for example, a single injection that protects cattle against both intestinal and lung worms, as well as certain external parasites. 

This characteristic also allowed the drug to target parasites that had been difficult to reach with previous therapies. For instance, “blood worm” larvae were much more commonly found in the blood vessels of horses before the advent of ivermectin treatment. Similarly, prior to ivermectin, there was no simple, effective way to protect dogs from deadly heartworm disease—but today, just a small monthly dose given orally eliminates heartworm larvae and prevents development of adult worms in the dog’s heart, lungs, and surrounding vessels.

Moreover, ivermectin’s unique systemic activity was found to have a sustained effect, allowing it to impact parasites over a longer time span. This meant the drug could not only treat a current infestation, but when used strategically could break the parasitic life cycle, thus helping remove parasites from the animals’ wider environment.

Unprecedented Potency

Possibly the most revolutionary aspect of ivermectin was simply its potency. The drug proved effective against even the toughest parasites that were especially hard to kill, or those that had developed resistance to other drugs. A prime example: certain stomach worms found in cattle were once difficult to eradicate because their larvae enter a state of “arrested development” for weeks or even months, during which time they are unaffected by traditional anti-parasitic drugs. But ivermectin proved active against even these elusive “hibernating” pests.

What’s more, its potency came at an unprecedented scale, with efficacy at doses many hundreds or even thousands of times smaller than previously used drugs. Parasites that had once run rampant, especially in production animal environments, and had to be battled repeatedly with large quantities of older parasiticides could now be controlled or even eliminated with much smaller, targeted doses of this new “wonder drug.” This, in turn, allowed for innovative new formulations and more convenient modes of administration. Ivermectin truly opened the door to a new, more strategic era of parasite control. 

An Ongoing Revolution

First commercialized for animal use in 1981, ivermectin swiftly became the first “blockbuster” product in the animal health sector, as study after study confirmed its efficacy and utility against more and more parasites, in a variety of host species, and with an excellent safety profile. It successfully addressed many persistent challenges, from the burrowing grubs of warble flies that once plagued the leather industry but have now become rare in many countries, to sarcoptic mange—an irritating skin infection caused by parasitic mites—that impacted the pork industry in years past, but is much less of a concern to many pig producers today.

Over the years, scientists at Merial and elsewhere have developed new formulations of ivermectin and related drugs to address specific parasite and host animal species, environmental factors, and administration challenges. For instance, the related drug eprinomectin was specifically developed for use in dairy cows because of its favorable residue profile. Other extended-release formulations allow for multiple doses over time without the animal being subjected to the stress of repeated handling—a technology only possible because of the drug’s unique characteristics.

It was because of ivermectin’s strong and early success in animal health that research was initiated to investigate the drug’s potential against human parasitic disease—work recognized decades later with the Nobel Prize. But perhaps equally important has been its indirect benefits to human wellbeing through its veterinary use, bringing us all healthier livestock, more productive food industries, and better lives for our beloved pets. That kind of impact is truly what defines a “wonder drug.”