Hi PV,
Here's a good trick (works for any age -- child or adult).
1. Chill the medication well (most liquid antibiotics should be kept refrigerated, anyway). You can place the bottle in a an ice water bath mixed with some salt, which will lower the temperature well below refrigerated temp, but keep it above freezing (which would destroy the chemical function of the antibiotic). BTW, salt lowers the freezing point of water (remember HS chem?).
2. Chill the child's mouth by having her suck on a popsicle for several minutes. This numbs the taste buds.
3. Pop the popsicle out, quickly spoon or squirt the medicine in. Your child will barely taste the bitterness of the antibiotic and it should go down pretty easily.
I hope this works for you!
R.