
We have been giving our 55lb Lab a 900mg tablet of glucosamine with chondroitin twice a day, with meals, for about 4 years now. We just buy regular people tablets and take the same ones ourselves. Our Vet approves. There is a veterinary version available but it costs way more. This is more of a preventative though. If the arthritis is advanced I don't know if it will do much good.
When Jet first came up lame arthritis was suspected but could not be detected on xray. Nevertheless we put her on a series of Cartrophen Vet injections. This was a miracle drug and results were noticed immediately, effectively confirming the diagnosis of arthritis. I begged the Vet to inject my poor old shoulder and it is supposed to be released for human use. After the first four injections booster shots are required and the interval differs from dog to dog; maybe one/month to one/year.
P.S. I'm in Canada so don't know if this drug is available to you. You could do an internet search for more info. on it.