I would echo the advice of the moms who say to give him some choices and control over how to take the medicine. But not a choice about TAKING it. I realize that I have not had the same experience with having a child associating doctors and medicine with surgery or other traumatic things so young. But, I really wonder how much he remembers from the ages you describe, and how much of his anxiety is reading YOUR anxiety about it.
I'm not trying to blame, just wondering... it would certainly be logical for you to be apprehensive about Dr care and medications for him. Perhaps he has learned some anxiety about it from you. It is AMAZING how much kids mimic what they read from the adults in their world. I always tried to project to my kids that they could have some control, but that there was no question that they WOULD do certain things (taking medicine for example). Because, well, there really isn't a choice about it. BUT, they can choose to hold it themselves, to drink it from the measuring cup, to take it out of a syringe, to let me pour it in their mouths, etc... They can choose to take small sips, or drink it all in one shot. They can choose to follow it with water or with juice or gatorade. They can choose to hold the chaser drink or to let it sit on the counter until they are ready for it. And on and on and on. They can do it in the kitchen, they can do it in the bathroom, they can do it on their bed. Whatever. I usually had them in the kitchen just because that is where the meds were, and I'd call them to me to take them.
If they were sick in bed, then I took the meds to them and carried a hand-towel in case there was a spill (never once thinking they might spit it out or throw it up--although a towel would be handy for those too).
My son had bronchiolitis at 2 yrs, and had to have an x-ray. Husband had to hold him down on the table (while he was kicking and screaming) to have it done, b/c we thought I might be pregnant and I couldn't be in the room. Husband swore that day he would NEVER. EVER. do that again. Son was okay as soon as he was back in the treatment room and the scary machine was out of sight.
Son was in the ER at around age 5 (I suspect it was toxic synovitis--he couldn't walk--but they never diagnosed it). They had to draw blood. A couple of tubes. He was scared, upset and it hurt. But when we left the ER (eventually) he was walking and happy again.
He has pneumonia at age 11, and had to get 3 huge injections in his rump. He cried it hurt so bad. Was sore for DAYS where they did the injections. Swore off ever getting another shot of any kind. He now goes regularly (as in weekly) for allergy shots---to the same doctor.
I really think how things are presented, and the vibes YOU give off, have a HUGE impact on how kids respond to things. Take a deep breath, and be honest with your son. "Son, I know you don't like medicine, and I know you don't want to take it. But you have to take it so you can get better. You can take it by ____ or I can give it to you by ____ . Which way do you want to do it?" (and then wait. Let him think about it. Let him decide in his own time. It really won't matter if it takes him 5 minutes to decide. Let him ask questions. Be honest in your answers. "Will it taste bad?" "Maybe. Everyone's taste buds are different. It will be better than vinegar. But you can have ____ as soon as you finish swallowing. Do you want to hold ___ or do you want me to hold it for you until you are ready for it?"
Good luck with this. And remember, when he is 10, he isnt' going to remember any of this.