We give Benson antihistamines periodically, and when he is on them he eats like a horse, whereas usually he is a picky eater.
The vet did tell us they do make dogs more hungry, so perhaps your dog is also wanting to eat more then usual when given the antihistamines?
Not sure how heavy Bronte is right now (female Wei, will be two in June, was 30kg at last weigh in), but she does really love her food :D