"The initial reaction from taking that one pill was horrible," Bergen said.
"One pill?" Strickland asked.
"One Trifexis pill was all he ever had."
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.
"I do feel deceived. I do not feel there was full disclosure," Bergen said.
TV commercials list side-effects like vomiting and lethargy, but not death.
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.
"I see that as a cause for investigation, and as they're looking at those causes. I feel confident the FDA will follow through, but from our experience, we haven't seen it," said veterinarian Toby Carmichael.
Carmichael said he and his partners have prescribed 75,000 doses of Trifexis with no adverse complications.
"My dogs have been on Trifexis since it came out and haven't had an issue once,” Carmichael said.
Physician Rochelle LePor has given her 7-year-old rescue dog Cooper nearly 40 pills over three years.
"I can only speak of my experience. For me, it’s like a wonder drug," she said.
"The FDA is not going to allow a product on the market that's going to hurt animals," Carmichael said.
Reports to Elanco's customer hotline have had an impact. There are now nearly 1,500 complaints of lost muscle control, a condition called ataxia.
Elanco added ataxia to its list of side-effects two years ago.
Elanco also added seizures, the malady that hit a prize bulldog named Foxy, owned by 50-year veteran breeder Nancy Harrison.
The dog developed additional symptoms beyond her veterinarian's control.
"So you were forced to euthanize her?" Strickland asked.
"Yeah, if you saw it, you wouldn't want to live with it either. And never in 52 years had I had one before,” Harrison said.
Harrison stopped using the drug, even though her other dogs handled it without issue.
"It's hard to lose a dog. They're my children," Harrison said.
The mystery of their dogs’ deaths eats at her and Bergen.
"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.