I am not a vet. I did discuss this situation with my vet and he approved my plan for trying to treat my arthritic rat. There are no known risks associated with this treatment but please seek the opinion of a vet before attempting this treatment with your rat.
In the course of breeding a friendly, up-til-then healthy strain of Fawn Rex Dumbo rats, I discovered that one particular line produced a female rat who got what appeared to be arthritis at a young age. Her joints became swollen and locomotion became less graceful. In her sister's litter there were two more young females with this condition so I chose to close that line down for breeding purposes and keep or place the babies as pets, with strict warnings against breeding them. I gave one of the females away before she became arthritic (in checking up on her later I found that she had developed the condition) and kept one to care for myself. Her name is Marinda.
Until four weeks of age, Marinda was a healthy, normal little rat. Then her paws began to swell, first in front, then, less drastically, in back. I started to research arthritis since all the symptoms (loss of flexibilty, swelling and inflammation of the joints, etc.) were a dead ringer for arthritis. I wanted to give Marinda back as much flexibility as possible and keep her pain-free. I tried a supplement or two, something related to grapes that I had heard about, and although it reduced the swelling a little it wasn't enough. Then I asked my vet about Glucosamine/Chondroitin on a tip from a good friend of mine who had used it on her horse. It is a supplement that provides essential nutrients which are diminished when arthritis occurs, substances that keep the joints lubricated and the cartilage intact, according to the article that I read at the vet's office (this was in Dog World Magazine, as I recall, probably the December issue). In discussing it with my vet (Dr. Zabel in Sugar Grove, IL, by the way, for any Illinois rat fanciers who may need a cooperative vet), we decided that there was very little risk to Marinda in trying this supplement since these substances are normally present in the body anyway in some quantity, and since none of them had potentially toxic components. Also, Dr. Zabel had seen good results with the use of these compounds for treating arthritis in dogs. We decided that the risks were minimal and the potential benefits strongly outweighed them. On the way home I stopped at Wal-Mart and bought Extended Release Glucosamine and Chondroitin dietary supplement (made by AmeriFit). It comes in caplet form. Suggested dosage for humans was six tablets per day. Cutting that down to rattie size and adjusting for the rapid metabolism of ratties, I thought to start out at 1/6 tablet per day, crushed, added to a tasty food for rapid consumption. Each tablet has 250 mg. glucosamine and 200 mg. chondroitin.
Starting with the above dose, I began to watch for changes. I noticed some improvement within about four days, mainly a slight improvement in Marinda's mobility and a more noticeable reduction in swelling. Since I had learned from Dr. Zabel that toxicity was very unlikely I decided to use a higher dosage and see if I could get better results. I bumped the dose up to about 1/4 tablet per day, crushed and served as before in soft food. Then I began to see better results. The swelling went way down, not quite to normal proportions but definitely much much closer. Mobility improved quite a bit to where Marinda could walk pretty well. Her hands were still a bit stiff and her back legs are not as mobile as I would like yet, but perhaps more improvement will occur. Sadly, Marinda managed to get an inner ear infection as well and so (despite treatment with chloramphenicol) has balance problems. But she has continued to improve to the point where she can now hold food and climb up into her hammock and get back out again. She seems happy and, if a bit weaker than the others, generally well. She is certainly very excited about getting her daily treat with the medicine inside!!!
A FINAL NOTE
In the course of checking back with the owner of Marinda's sister, I saw the sister again and was shocked to see how swollen her feet were. The contrast between Marinda (who at that point had been on supplements for about two weeks) and her sister, who had not started them yet, was very marked. Since it was obvious that this treatment had not hurt Marinda and had most likely helped her, I encouraged Marinda's sister's owner to try this supplement for her, too.