Hi Robert,

Any sudden changes can be worrisome and it’s good that you had your cat checked out by your vet. Antibiotics themselves wouldn’t be likely to help with any allergic bumps unless there was a secondary infection. It may be possible for the diet change to cause an allergic reaction but with something so sudden, an insect bite would be more likely. That dose of Benadryl appears to be appropriate for your cat’s weight and I would follow your veterinarian’s instructions. It’s good to keep a log of incidences like this in case of future reactions.

I hope he’s feeling better now.

Dr. Ryan Llera