Help with anxious and irritable child

I work in a school where I'm in charge of 3 and 4 year old kids. There is this child that has epilepsy, his crisis are now controlled, however, he hardly speaks and doesn't socialize with the other kids. When he arrives at school he doesn't play with toys, and just sits with his head resting on the desk. When we give him a book to color he throws it to the floor and pushes away his crayons. After lunch he starts to get really irritated and spends the rest of the day crying because he desperately wants to leave the classroom; we have tried to distract him with toys we know he likes, but he doesn't want them and keeps crying and screaming. He can't be near the other kids because he bites them, pushes them or pull their hair, and the rest of the kids don't want to be near him anymore. Biting is something he does often, he's usually biting his hands or anything he gets his hands on. I also have to add that he takes medicine for his anxiety; for his epilepsy, and he also needs medicine to sleep well at night, but he is still anxious and he doesn't sleep very good.

I really need some advice. How can we motivate this child to work at school? What sort of advice can we give to his parents? We are all sort of getting desperate already.

Thanks in advance.