Which condroitin? There is a big difference in supplements. Same for MSM.
Deramaxx and rimadyl have the same serious adverse reaction % in dogs who have a reaction, at 23% death rate from oral (and with rimadyl, injection 23%) This is a percent as related to reactions, not total doses. Deramaxx is the worst on the stomach. Regardless of which one you use, you should add pepcid, tagamet or zantac to the daily regiment.
Metacam oral is 12% (death rate as a % of adverse reactions) as is etcogesic, however injectible metacam is 23%. Most of the dogs I've heard of have had various reactions to etcogesic and metacam seems to be the one best tolerated. Sure as I say that, he won't be able to take it
In addition to the normal supplements, there are chinese herbs that help arthritis. Of course, chiropractic and acupuncture provide tremendous relief when done on a continuing basis. With my guys, each one has been different as to the time frame needed between adjustments and treatment.
Some old ones have benefited from Duralactin. I tried it with Magic and saw no result, but she was very old and on a good regiment of other supplements.