Xylitol is prothrombotic and associated with cardiovascular risk
pubmed.ncbi.nlm.nih.gov
pubmed.ncbi.nlm.nih.gov
My dog did not get any xylitol BUT it was close -- he got stung by a bee, and was having difficulty breathing. And we received bad advice from a clinic to give him Benadryl. Which would have been good advice but for the fact Benadryl is VERY often sweetened with Xylitol. We got a 2nd opinion and better treatment from another emergency vet, by luck.
Where did you see Benadryl with Xylitol? They don't list it in any of their product ingredients, nor do they list it in their ingredient transparency page[1].
[1] https://www.benadryl.com/benadryl-difference/ingredients-tra...
To give an example, a typical hershey's milk chocolate bar is nearly impossible to kill your dog with, even if it's a small dog.