Poor Sawyer! I hope that he is feeling better by now...sorry that I didn't get to this sooner, although I don't have much insight on this...not from a canine perspective...but I know that humans can take something, say asprin, for years and then one day just become allergic to it.
I am glad that you were able to pinpoint this problem and get him treated. Bless his little heart.
I am glad that you were able to pinpoint this problem and get him treated. Bless his little heart.