The homeopathics do not interfere with the drugs. You may use ARTHRO-IONX or PROMAXOL to help with symptoms. I usually start with PROMAXOl but you can start with either. When I start with PROMAXOL, I use it until I see improvement and then switch to ARTHRO-IONX. Once there is significant improvement one can try reducing the amount given. With improvement you might also want to talk to your veterinarian about reducing the drugs which can be damaging to the liver and kidneys.
To dose the homeopathic I would split the dose and give a half dose with breakfast and a half dose with supper. You can give another two half doses through out the day if you need to. I would try to give it at a time away from the other medications so the body has time to focus on just the homeopathic. Once symptoms are under control you can switch to a whole dose once a day. In addition I would give PROBIOTICS and OMEGA 3,6,9 .
What kind of water and food do you give your dog? These can influence joint health too.
I would recommend having a veterinary chiropractor check your dog. It often improves movement. Acupuncture can also be helpful.
Please let us know how you do.