It's frustrating to have your dog react in the wrong way to a medicine that's supposed to be helping and it's expensive in emotions+$. You really need to notify your Vet as to the reaction and they need to document it + you will need a different medicine to cure the original illness. Was the original injection the same as the tablets? On the plus side is the fact that you have a known bad response to a medicine and, if there were ever a life threatening incident for your Cav, this medicine would not be complicating survival because you now have a known allergy reaction. good health, again.
Learning new things everyday