
I give my 55 lb Lab one/half of a 325 mg aspirin occasionally and once in a blue moon I will give her a whole one. My Vet is OK with this though they would be concerned if it was a regular thing as there are doggy meds, such as Metacalm and Cartrophen Vet, that are easier on the liver. But I'm only doing it maybe once a month, after a particularly energetic outing, to combat arthritis pain.
If your boy is reacting to shots I wonder if an antihistamine would be better? After consultation with your Vet of course. My Vet has also OK'd full adult strength Benedril for our girl after a suspected reaction to a bee or wasp sting. We carry it with us on canoe trips where access to the Vet is impossible.
Can I really, really stress that you should consult your Vet? Some breeds can react to stuff that others don't. I give my Lab things that my sister's BC cannot tolerate and I understand from her (and her Vet) that the collie breeds are sensitive to lots of medications.
oops, not sure if this landed in the right place. Meant for original poster.