Fact Check

Do Trifexis Parasite Prevention Tablets Kill Dogs?

Have Trifexis brand parasite prevention tablets caused the deaths of a large number of dogs?

Published Nov. 13, 2013


Claim:   Trifexis brand parasite prevention tablets have caused the deaths of a large number of dogs.


Example:   [Collected via e-mail, November 2013]

Trifexis medicine, which is a tick and flea preventative, has been noted it could kill your dog or cat. This was reported in Atlanta. Please
check his out if it is true or false.


Origins:   In November 2013, Atlanta television station WSB reported a story about dog owners in Atlanta (and elsewhere) claiming that Trifexis brand parasite prevention tablets had caused the deaths of their pets:

Grieving animal lovers across the country are coming forward blaming a popular pet drug for killing their dogs.

"It's like a piece of your heart is being torn out," said dog owner Beth Timms from Gainesville.

Her dog, Gizmo, died after taking Trifexis. The once-a-month pill made by Elanco is a combination pill for heartworm, parasites and flea prevention. (Elanco is the animal health division of pharmaceutical giant Eli Lilly.)

Timms emailed consumer investigator Jim Strickland after finding a Facebook page titled "Trifexis Kills Dogs."

Owners from all over the country have posted on the page, blaming the drug for their dogs' deaths.

WSB ran a similar piece in July 2014, stating that the number of death complaints related to Trifexis had gone up by nearly 40 percent since that first report (a common occurrence when consumers are warned about a particular adverse effect in conjunction with a given drug):

WSB-TV consumer investigator Jim Strickland has discovered that hundreds more pet deaths are being blamed on Trifexis, a popular dog medicine designed to kill fleas, control parasites and prevent heartworm.

Since Strickland first reported data collected by the Food and Drug Administration eight months ago, the number of death complaints is up nearly 40 percent, now coming in at a rate greater than one dog per day.

The FDA said there is no solid evidence linking Trifexis to any dog's death. The reports are simply complaints from owners and vets in which the pill is suspected.

[Anita Bergen's] Scottish terrier, Fergus, was 10 years old when she tried Trifexis.

"The initial reaction from taking that one pill was horrible," Bergen said.

Bergen said the dog lost all muscle control, lost his thirst and suffered liver failure. She euthanized him two months after giving him the pill.

Strickland learned through the Freedom of Information Act that the FDA lists 965 complaints of dog deaths blamed on Trifexis.

That's an increase of 38 percent in the last eight months, and close to the total of 1,000 deaths linked to Chinese-made chicken jerky pet treats.

Drugmaker Elanco said it can find no link between the pill and any dog fatalities.

"All the tests that are done, they're all inconclusive. No one can ever say this death is absolutely the result of administering this particular medication. But all the owners, all the pet caregivers know," Bergen said.

The FDA said it's continuing to monitor reports and considers the product label a living document. To date, there are no plans to list death as even a rare but potential side-effect.

However, WSB noted in a follow-up to their original report that a pathologist hired by Trifexis had found no causative connection between the deaths of dogs who had reportedly died after being given Trifexis and the drug itself:

Consumer investigator Jim Strickland obtained documents from a pathologist hired by drug maker Elanco that said three puppies did not die from taking the drug Trifexis, made by Elanco.

"Trifexis played no role in the death of this dog," Dr. Jeffrey Engelhardt wrote.

In the case of three dogs, Engelhardt said Trifexis' involvement was unlikely. The dogs died of heart failure in September [2013].

Engelhardt did not examine the dogs' remains, only their pathology reports.

The three [dogs] that died had one dose of the drug and became weak and lethargic. Two of the dogs died three weeks after taking the pill. One died in six days.

"We have not been able to identify with all of these reports, any specific trends we can link directly to the use of the product," said Elanco veterinarian Dr. Stephen Connell. "Certainly we want to investigate these cases. We want to get to the bottom of this as much as anyone does."

Elanco insists any side effects are mild, not fatal.

Necropsy reports on three of the dogs mentioned in the WSB news report as possible Trifexis-related deaths (Bishop, Tucker, and Jade) indicated that the canines died of heart-related ailments (myocarditis and endocarditis).

Veterinarian Doc Cleland also posted on his College Park Vet blog that he had not seen any studies indicating a positive correlation between Trifexis and death in dogs and that he would continue to use and recommend the product:

I've seen and heard a lot of concerns over the past several days about Trifexis and how it kills animals. I even visited the "Trifexis Kills Pets" facebook page and looked around there. ELANCO has sent us a fax about their stance on Trifexis. So where do I stand?

Plenty of animals receiving Trifexis die. However, plenty of animals receiving love and attention from their families also die. What has to be present with any medication

or situation is a positive correlation between (a) and (b). If animals receiving Trifexis causes more deaths or problems than animals without, then there is a positive correlation between Trifexis and death. Cause — effect.

With that said, I have not seen any studies to point to this positive correlation between Trifexis and death. ELANCO itself reports an increase in upset stomach in animals receiving Trifexis, and they warn that seizures may be positively correlated with Trifexis. However, there have been no other patterns of adverse events noted either before or after Trifexis was released onto the market. Correlation is everything.

Will I continue to use and recommend Trifexis? Yes.

Are you crazy if you don't use Trifexis? No. Make sure they are on some form of heartworm and flea prevention. I would also recommend that you educate yourselves with information, studies, side effects, and evidence based medicine for whatever product you choose.

Elanco, the parent company of Trifexis, eventually released a statement in July 2014 asserting that a thorough review of Trifexis reports which had been subitted to the FDA found "no established link between Trifexis use and death":

In the United States alone about 70 million doses of Trifexis have been dispensed and 15,000 veterinary clinics rely on the product. Elanco and the FDA conduct continuous, on-going monitoring on Trifexis, and all products, to determine if there are any signals or trends in the data, any increases in frequency of certain types of reports, etc.

We’ve seen no significant changes in reporting rate from year to year over the life of the product. In fact, we’ve recently completed a thorough review and analysis of Trifexis reports that mention death and have presented that to the FDA. There continues to be no established link between Trifexis use and death.

It’s critically important to understand that reports are not an indication of cause. For any given ADE (adverse drug event) report, there is no certainty that the reported drug caused the adverse event. The adverse event may have been related to an underlying disease, using other drugs at the same time, or other non-drug related causes. Anita Bergen’s case illustrates that a report is not necessarily an indication of cause. This case includes a number of other factors including a pre-existing, degenerative neurologic condition, long-term use of an untested, unapproved product and a diet lacking appropriate nutritional balance. Further, Scotties are naturally predisposed to several of the conditions listed in this case. The data suggests it's unlikely there was any connection to the product in the pet’s unfortunate passing.

Also as we discussed, the data show this level of reports is similar for other products dispensed for heartworm prevention.

Last updated:   11 August 2014


    Cleland, Doc.   "Trifexis: Killing, Correlation, and Cost/Benefit."

    The College Park Vet.   12 November 2013.

    Strickland, Jim.   "More Owners, Vets Claim Dog Deaths May Be Linked to Trifexis Drug."

    WSB-TV [Atlanta].   31 July 2014.

    WSB-TV [Atlanta].   "Grieving Animal-Lovers Blame Pet Drug for Killing Dogs."

    12 November 2013.

    WSB-TV [Atlanta].   "Company Insists Flea Drug Not the Cause of Dog Fatalities."

    12 November 2013.

David Mikkelson founded the site now known as snopes.com back in 1994.