First of all, 9 years is not what I consider "up in age". I realize there is a time frame that you can do without, but this is just not practice that I have EVER heard of.
I have had MANY pups in my care with varying ages and conditions. Many have been on multiple medications and I have NEVER been told to take them off of heartworm preventatives.
Sorry, but I don't see that as acceptable practice at all. I realize that some homeopathic people don't agree, but I have had many foster pups who contracted heartworms because of the failure of others to protect them from them. The treatment is very hard on them...and they can die.
Just unbelievable to me that this was suggested.
To the OP: I
strongly suggest that you get another opinion about stopping heartworm medications. They are not contraindicated with Rimadyl.
Also, you might want to look at this website:
American Heartworm Society | Canine Heartworm
I suggest that you read that information and speak with your vet about this!