It is actually easier if they are screaming, because they have to swallow.
Getting meds into ours was a 2 person job. dh would have ds laying on his knee, one of dh arms under ds supporting the head and that hand securing ds arm, ds other arm pinned between him and dh and dh body pinning ds head in position, iyswim.
I would sit on the floor in front of them and hold his legs and use my body over him to make sure he couldn't twist around. I would blow onto his face while dh forced the syringe between his teeth and tried to avoid getting bitten. He'd angle it to the side of his mouth, as far down as possible and feed it in literally a drop at a time (it is practically impossible to spit out a single drop!) I'd blow at each drop. All the time we were telling him how much we loved him, and why he needed the medicine and how much better it would make him and what a brave boy he was....It could take 10 minutes to even get 5 mls in and it was so traumatic for all of us, but it was the ONLY way we ever found of doing it.
God it was horrible. But if the child HAS to have the medicine, you do what you have to do. No matter how horribly cruel it makes you feel . Sadly, if all else fails you just have to deal with feeling like the biggest shit on the planet, because they need the med.
This parenting lark can be crap sometimes, can't it? Sympathies to you, cos this is not a nice situation to be in.