Don't use a substitute Diphenhydramine HCl combined with Ibuprofin or you will poison your dog. In this case the brand name Benadryl matters.

I would recommend talking to your vet before you give your pets Benadryl as it can cause undesirable side effects.

At a minimum, make sure your pet doesn't have one of the contraindications for Benadryl: glaucoma, prostatic disease, cardiovascular disease, hyperthyroid, etc. And that your pet isn't taking one of the medications that create a harmful drug interaction with Benadryl.