Found on Facebook today:

Justice for Jack A Dog-Owner's Story of Loss and Raising Awareness

Dog Owners Beware
Posted on May 29, 2012 
One of our beloved dogs, Jack, a 6-year-old, chow-lab mix, died yesterday. His death was very unexpected and traumatic. Although, our dogs did not receive the same amount of attention as they did before Bobby was born, they were still loved dearly. Bob walked them religiously every single day. Jack loved, loved, loved, playing fetch. Tennis balls were his favorite. When we discovered that he had died, we began questioning what happened to our sweet Jack.

On Monday, May 7, we took both of our dogs to our vet for their annual check ups. It was a very routine visit. They were both checked for heartworms and parasites, weighed, and listened to. They were deemed normal and healthy. They both received their rabies vaccinations, and a new drug (via injection) that was recommend by our vet, ProHeart 6. Our vet simply said, “Hey, we have this new shot that we can give them for heartworm protection instead of an oral preventative. It’s easy because it’s only one dose every 6 months.” Sounded good to us, so we agreed. That was it. That was all the information we received, and—by our own fault—all we asked for.

Both of the dogs seemed fine the first week home, then Jack started acting differently. He didn’t want to go on his daily walks. He didn’t want to fetch his tennis ball. He didn’t want to eat his dog food. My husband even tried giving him some leftover steak from our dinner, and Jack wouldn’t eat it. We knew something was up, so we took him back to the vet on Monday, May 21.

The vet discovered that Jack had a fever, but could find nothing else wrong with him. He was given a steroid shot and some antibiotics in case he had an infection, and we were sent home. Over the next few days, Jack seemed to feel better. He was still a little lethargic, but was eating and perked up when we threw a ball or petted him. He seemed on the mend. We thought he must have just had a virus and was getting better. It did not even cross our minds that he was so gravely ill, so we continued with our Memorial Day plans to go to the beach.

We returned from the beach to a grim discovery—Jack dead in a pool of blood and vomit. His poor little body was crumpled up in a strange way, like he had literally just fallen over dead. We took him to an animal ER where they confirmed that he was dead, and we paid to have his body cremated. The vet at the animal ER stated that it appeared to be a heart attack or cardiopulmonary problem that killed him.

That evening, as we wrestled with grief and trying to explain death to our 3-year-old son, we began to question what on earth had happened to our previously perky puppy. Okay—he wasn’t a puppy, but he always behaved like a frisky, fun puppy, and he certainly wasn’t an old dog. We considered the possibility that he ate something bad, but his vet had all but ruled out a GI problem. We went over and over what was different, the only thing we had changed was their heartworm medicine.

We googled the shot he had received a few weeks earlier, ProHeart 6. The drug was originally made by a division of Wyeth Pharmaceuticals, but the drug company Pfizer acquired Wyeth and all of its holdings in 2009. Pfizer’s own website lists side effects of the drug as lethargy, loss of appetite, vomiting, and death. (Source: Pfizer) Jack had exhibited exactly all of those symptoms… in that order.

After doing further research, we also discovered that the drug was originally pulled off the market in 2004 for a high rate of adverse reactions to the drug. “According to an informed veterinarian, ‘Proheart caused more deaths in one year than all of the oral heartworm preventives combined did in ten years. When the FDA notified Pfizer that their drug was causing a problem, the manufacturer claimed it was due to the vaccines’ being given at the same time. The FDA looked at the data again and told them the dogs involved had been getting their vaccinations all along and the only difference was the Proheart. That’s when the FDA informed the company of their intent to pull it and the company then voluntarily took it off the market.” (Source: The Senior Dogs Project)

Pfizer was allowed to re-market the drug in 2008 with the following stipulations: Pfizer agreed to add additional warning labels to the drug packaging, and agreed to mandate that pet owners be given a drug fact sheet and be made to sign an “informed consent” document. Pfizer went even further as to mandate web-based training for veterinarians who gave the drug, and issued several “Dear Doctor” letters to all veterinarians regarding the adverse effects of the drug. (Read one of the “Dear Doctor” letters here.)

The part that bothered and alarmed us the most was this line from the drug’s website: “ProHeart 6 dog owners must be advised of the risks of ProHeart 6 and sign an Owner Consent Form prior to the first administration.” (Source: Pfizer)

We were never shown a fact sheet on the drug, never “advised of the risks”, and certainly not given an Owner Consent Form” by our vet to sign. (In hindsight, we feel that we should have asked more questions about the drug, but we trusted our veterinarian.) If the side effects had been presented to us as they have in our research, we would NOT have consented to have Pro Heart 6 administered to our dogs.

We also found some literature suggesting that ProHeart 6 should not be administered at the same time as vaccinations: “Allergic reactions, sometimes serious, have been reported when ProHeart 6 and vaccinations have been given at the same time. Talk to your veterinarian about the risks of administering ProHeart 6 at the same time as vaccinations.” (Source link here.) Our vet administered ProHeart 6 at the same time as Jack rabies vaccine, and distemper/bordetella.

The drug’s information page from states the following: “Owners should be advised of the potential for adverse reactions, including anaphylaxis, and be informed of the clinical signs associated with drug toxicity. Owners should be advised to contact their veterinarian immediately if signs of toxicity are observed. The vast majority of patients with drug related adverse reactions have recovered when the signs are recognized and veterinary care, if appropriate, is initiated.” (Source:

When we did recognize that something was going on with our dog, we did what we thought good pet owners are supposed to do. We took him back to the vet. The vet should have recognized that he was having an adverse reaction to the ProHeart6 that she administered to him (without our “informed” consent) only weeks earlier and treated him appropriately. If the vetrinarian had recognized his symptoms, he could have recovered. She did not, and as a result, our otherwise healthy dog died. Now, we are left waiting on the drug to work its way out of our remaining dog’s system praying that she does not fall victim to the same fate.

Stories of dogs that died as a result of being administered this drug are abundant. Check out any of the following links for more information, and please, ask for all of the facts, side effects, and more information when your vet (or doctor) recommends this drug (or any drug). ProHeart 6 provides no additional benefits or protection than safer, oral heartworm preventatives.

Additional Resources:

Letters & Data by the Drug Manufacturer from the FDA’s Website:

July 22, 2002 “Dear Doctor” Letter warning of additional “adverse reactions”

June 19, 2003 “Dear Doctor” Letter advising of label changes due to “adverse reactions”

“Risk Minimization Action Plan” for the Re-Introduction of ProHeart 6 to the Market (63 Pages which includes the newest precautions, and the actual drug label, “Client Information Sheet”, and “Owner Consent Form”—none of which we were ever given.)



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Thank you for posting this warning, Lynne. My heart goes out to this family in their loss. I am grateful they took the time to expose this drug reaction and hopefully save others from the same result, a terrible experience of grief.


Scary what is allowed to be on the market, because it's for a dog.

Indeed it is! Scary too, that dogs are still used to product - and safety- test drugs and other items for use by humans.

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