In short, he's got a cat. He's sick.
So he went to the vet, who gave him a medicine, which he gave the cat. Within 20 minuets, his mouth is full of bubbles. They come out with some blood. What's wrong, and what should be done? This question requires an immediate answer, like right now. Please contact him directly, as I've got to go off-line:
The vet is out of reach, so your knowledge matters. Spare compassion messages this time, because this seems like a real emergency.