Gave our cat prozac and now he's hiding

Our cat Plutonium was diagnosed with FIC and his flare ups have been bad enough that the vet prescribed prozac to handle his anxiety that'striggering his flares. We tried for 4 days to give it to him in wet food, but he started turning his nose up to it so tonight we tried injecting it right into his mouth. As soon as we let him go he ran around the house poofed, smacking his lips, drooling and wouldn't let us get near him. Now he refuses to come into the living space where we, his food, water, beds and toys are. He just stands at the top of the stairs; he'll take pets, but won't cross the living space threshold. I don't know what to do, he was so upset and I don't want giving these meds to make him more stressed or break his trust. I'm not sure I'm doing the right thing, but at the same time I can't meet him where he's at without help. Currently he screams all hours of the day, worse so if either my husband or I am gone and he hates when we focus on anything that's not him. I know he needs something, but is this the right thing after that type of reaction?