For many of us, our pets are as important to us as our human companions.

That's why some dog owners are warning people about a drug that is killing some dogs.

"We want to give someone else a chance to know the side effects of this drug. We weren't given those side effects."

Paul and Tammy Michelfelder say Rimadyl drug killed their dog.

"The Vet put her on Rimadyl for arthritis that was supposed to help her get by."

They said they were told Rimadyl would make Scarlett a new dog.

Pfizer used to run TV commercials showing dogs acting like puppies after taking Rimadyl. Pfizer has pulled the ads.

Instead of seeing results like the commercial showed, the Michelfelders watched Scarlett get sick -- fast.

Paul Michelfelder said, "Friday we noticed the same thing, no appetite, we got up Saturday morning and Tammy looked at the dog and she was yellow,"

"I went and got a flashlight and she was just laying in the grass and she couldn't get up," Tammy added.

"Now we were put in the position at that point to put the dog down or give her a fighting chance," Paul said.

They spent several thousand dollars fighting what the veterinarian noted as "Rimadyl toxicity." 

The Michelfelders say they eventually had to put Scarlett to sleep. Her ashes are held in a box to remind the family of their beloved pet.

The Michelfelders have joined a class action lawsuit against Pfizer. Also participating in the lawsuit is Michelle Walsh. Walsh says she was one of the first to lose a dog.  She then helped found a national organization called B.A.R.K.S. -- Be Aware of Rimadyl's Known Side Affects.

"Let my dog be an example. There's no feeling like knowing you just killed your own dog."

Michelle feels Rimadyl killed her dog named Samantha, and she says the dog she still has, Gwendolyn, survived the drug, but barely.

"Gwendolyn is in almost complete liver failure. We're hanging on by threads."

These two incidents were among thousands of complications reported to the Food and Drug Administration. The FDA says its Center for Veterinary Medicine was swamped with Rimadyl complaints of Adverse Drug Events also called ADE's.

The FDA reports more than 10,000 ADEs in 3 years. The FDA says about 1500 of those are deaths.

The FDA says it insisted that Pfizer include the word "death" in their Rimadyl commercials. The Administration says Pfizer didn't want to use the word death -- and pulled their ads instead.

Pfizer added an insert to the Rimadyl packaging which does include the word "death," but people like Paul Michelfelder say it's not informative enough.

"Had a vet told me a possible side effect was liver damage, there's no way I would have put that dog on that drug. No way."

The FDA also told 5 Investigates that "Veterinarians are now the weakest link in the Rimadyl chain."

The FDA is planning to try to further educate vets on the potential dangers of Rimadyl. 

No one seems to deny -- Rimadyl is a useful drug.  Pfizer veterinarian Dr. Malcolm Kram told 5 Investigates that it remains the most important drug in treating canine arthritis.

Dr. Malcolm Kram told us, "We've used Rimadyl in over five million dogs with the overwhleming majority of these animals having improved life, improved movement and in many cases actually saving them from euthanasia where they otherwise would have been put to sleep because they just can't get around like they used to."

Many other vets and the FDA confirm this. Even Michelle Walsh believes Rimadyl can be useful.

Talk to your vet.  Do your own research.  And because the side effects typically happen very quickly, monitor your pet carefully.

The FDA told us the potential side effects are just as likely to affect young dogs as older ones.  We cannot emphasize enough -- monitor your animals carefully and talk to your vet about getting liver tests soon after putting your pet on Rimadyl.

Also, if your dog was previously using this drug, you may want to get in touch with Pfizer, the FDA or B.A.R.K.S.  You will find links at the top right of your page.

E-mail 5 Investigates' reporter Chris Hayes.