Primor reactions

Have you ever seen a dog become lame and have swelling on multiple limbs?  My dog was put on primor 1 month ago for only a few days and no problems, we just started him on it again and he has been on it for exactly 1 week, He has suddenly developed a swollen front right paw, his rear hock and leg are swollen, and he has had some hive like swellings throughout his face and body. He is also having difficulty getting up in his rear legs. We need to help him get up. Once he is up, he limps a little and then is able to walk it off. He is unstable on his back end and if he loses balance he falls. He is a 220 lb mastiff. It is my understanding that this medicine can cause some type of a arthritic problem in the joints. If so, is it reversable? Please help with any advice you may have. He is not even 3 yrs old  and it pains us to see him like this. He still is alert and responsive and wags his tail. He was given 2 1/2 cc of Dexamethasone inj yesterday and some of the hives have gone down but his legs are still swollen and he is still having trouble getting up in his rear.  We have stopped the primor and put him on Deramax for pain. It looks like he may have fractured two toes in the front right paw. The radiographs were not really clear so he has a splint on just in case. He is sensitive on that foot when you touch his toes. Thanks

[Kimberly Coyner, D.V.M., DACVD]

Yes, in rare cases sulfa drugs such as Primor can cause unpredictable drug reactions, with symptoms such as swollen painful joints, or in severe cases skin ulcerations or liver disease. Primor is an excellent skin antibiotic and I use it often, but if side effect develop, it should be immediately discontinued, and symptoms usually resolve within 1-2 weeks. In the future, Primor and related sulfa drugs should be avoided in your dog.
Good luck,
Kimberly Coyner, DVM DACVD
www.dermvetvegas.com