Hello and thank you for you post. Arching of the back can be a sign of abdominal or back pain in dogs. Is linus eating/drinking or having any vomiting or diarrhea. Those signs would suggest gastrointesintal signs and abdominal discomfort. Is Linus having any difficulty walking or hesitant to going up stairs or jump on/off couch. Those signs would suggest back pain.
If Linus continues doing this I recommend having him examined by your veterinarian.
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I have touched him all over and pressed on his back and legs with no visible reaction. His tummy is flat with no signs of bloat (he's a dane) but is firm. Every so often he has a loud "explosion" of gas but it doesn't smell particularly bad. He did take some water but refused a favorite treat and won't lay down, just keeps pacing.
When you explain a loud explosion of gas to you mean that he is passing gas rectally, or he is burping?
One of the classic signs of bloat is burping and retching without actually bringing any thing up. Linus will almost look as if he is vomiting but again not bring anything up.
The pacing may also be a sign of pain. Again if he continues this he should be examined. It may be a good idea to go to an emergency clinic this evening to have him checked out.
Not sure what medication will help him as I do not know whats wrong with him without examining him.
I typically do not give pepto to dogs. But you can try some Pepcid AC. He can take 10mg twice daily.
Again if he continues to be restless and acting painful then he should be checked out.