Sigh...this is hard...when it was our problem, we actually had some doctors tell us "you just have to be the bad guy, stand up and be a parent and just give him the medicine" and I was thinking, my kid made himself vomit instead of taking it; YOU make him take it!
My doctor first off suggested different flavors. Our K-Mart pharmacy (and maybe Walgreens?) will alter the flavor of medicines for kids.
That said, the antibiotic my kid was on was AWFUL. We ended up dumping two full bottles down the sink, and I could smell them for days--I can't blame him for not wanting that!
We had him on steroids for a severe allergic reaction, and opted for the pills. I crushed them good, and then put them in sweet and strong flavored foods--a berry smoothie (with tons of sugar), yogurt, pudding, ice cream--and that actually worked better. It did NOT work for us to hide the liquid antibiotic in ANYTHING--but if you haven't tried that, i'd try that, too.
Ultimately, our doctor did say she could give our son a shot--which kinda worked; he's afraid of shots--but I also think it just made the fear a lot worse, too.
Anyway--it's hard; I sympathize. Good luck.