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MIAMI (CBSMiami) — For Joe and Liz Birch, a life without their yellow labrador retriever, Zoe, seems incomplete.

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They brought Zoe home 15 years ago.

Before their kids, Abby and Jack, Zoe was their crash course into parenting.

It’s safe to say that Zoe is a huge part of the Birch family.

“I feel like we’re on borrowed time because the average lifespan is 12 years and with Zoe at 15-plus I feel like every day is a gift,” Joe Birch said.

As each year passes by, thoughts that Zoe’s time with the family is limited pop up from time to time.

“Especially now that she’s 15 and a half and for a lab that’s very old. Yeah, every time you think of a holiday passing by you think is that dog gonna be with you? Will she be with us for the next one?” Birch asked.

The Birchs have done everything possible to keep Zoe active with several daily walks, giving her an anti-inflammatory and a doggie ibuprofen to help with arthritis.

“When she starts…back legs start to slide a little or she hesitates when we go for walks, you always wonder if it’s the beginning of the end for her,” Birch said.

For the Birchs, who’ve had Zoe for longer than their own children, watching her age over the past 15 and a half years has been a hard thing to see. They say they’d do just about anything to keep her around.

“If there was a medication that would make her feel better, depending on what the side effects were I would definitely want to try that,” Birch said.

American Aging Association researchers Dr. Arlan Richardson and Dr. Matt Kaeberlein say they may have found something that can do just that with Rapamycin.

It’s an immunosuppressant drug already approved by the FDA.

Rapamycin is currently used as part of a drug combination to help organ transplant recipients and also to treat certain types of cancers.

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A little over 10 years ago, Dr. Kaeberlein started working with Rapamycin to see what effect it would have on aging.

“This drug has pretty incredible effects in terms of increasing life span and improving life in aging in every laboratory where it’s been tested,” Dr. Kaeberlein said.

Kaeberlein who’s a researcher at the University of Washington MedicalCenter, felt so strongly about the positive results Rapamycin showed in mice, that he got enough funding to spearhead “The Dog Aging Project.”

Twenty four medium to large dogs, ages 7 and 8, which is considered middle aged for dogs, were a part of the study.

Dr. Kaeberlein and others focused primarily on cardio function.

After the 10 week study, they found that the dogs given Rapamycin appeared to reverse some measures of age-associated cardiac decline with no negative side effects. He says based on the research, it stands to reason that Rapamycin could increase lifespan by about 25 percent or 2 1-2 years for a dog that would normally live to be 10.

That’s the exact amount of time Dr. Richardson from the Reynolds Oklahoma Center on Aging has given the drug to his now 15-year-old dog MoMo.

“I understood the potential negative consequences,” Dr. Richardson said.

After studying human aging for 40 years and learning about Rapamycin 6 or 7 years ago, he was able to get his veterinarian to prescribe the drug when MoMo was diagnosed with Mitro-Valve Disease.

“They said it could vary…they said it could be anywhere from 6 months to a year…year-and-a-half so she’s doing pretty good,” Dr. Richardson said.

While Richardson’s dog and the dogs in the “Dog Aging Project” didn’t have negative side effects, in higher doses given to human transplant and cancer patients, the drug is known to cause mouth sores, higher triglyceride levels and impaired wound healing and in mice – raised insulin levels.

It’s also relatively expensive with current prices for dogs at a couple hundred dollars a month.

Richardson has no regrets putting MoMo on the drug and says he would even take it himself one day.

Meanwhile, Dr. Kaeberlein says while the research is promising, much more needs to be done before it becomes mainstream.

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“The whole reason why we need to do this study is to really determine does it work the way that we want it to in dogs and is it safe in dogs and so it’s premature for me to start recommending to pet owners that they go ask their vet for Rapamycin,” Richardson said.