Our elderly dog (she'll be 13 in a couple of months) got a passing grade after her course of antibiotics last month. When we were at the vet we talked about her waning appetite and what is most likely arthritis in her hindquarters, both common in older dogs.
The vet told us that the acid-reducing medication Pepcid can sometimes have an appetite-stimulating effect in dogs, and the pills are inexpensive (a box of 30 was around $4 at Target) so we started her on those, one pill per day, and we have seen moderate results. She still isn't eating as much as we think she should be, but she has added back about a pound and a half so far.
For the arthritis she prescribed tramadol, a pain medication that is also given to humans. It's also inexpensive; 28 pills were around $12, and she's getting half a pill twice a day, so those will also last about a month. Of course, this means we have to get her to take three pills per day, so as I mentioned before we are using chicken salad as an enticement.
I figured tuna would work as well and buying it canned is a good bit less expensive. But after about a week she started to express a lack of excitement for the pill-packed blobs of tuna. It seemed to be because the tuna was slightly "wetter" and did not stick together quite as well, but that's a variation that I should be able to alter with another batch. She could just be expressing a legitimate preference, or just really likes chicken salad a lot more than tuna. Spoiled much?