A million-dollar wound or Blighty wound is military slang referring to a type of wound received in combat which is serious enough to get the person sent away from the fighting, but is not fatal, nor will it leave the person permanently crippled.
In conclusion, Benadryl does not cause kidney damage directly, but if you uses excessively over a long period of time and there is urinary retention, the chronic urinary retention could ending producing kidney failure.
Humans who have taken Benadryl know that one of its side effects is a sedative one. In fact, the active ingredient in Benadryl, diphenhydramine, is sometimes prescribed to both humans and cats for this effect. It also has an anti-nausea effect, which can be useful in preventing nervous cats from getting sick.