DD is on Zantac too. She's ......... 2 days older than your bub. wow, cool!! hehe.
Try putting the syringe diwn the side of his mouth. Between the cheek and gum.
You need to put it in a fair way. Also try cradling him so he's tilted back. Gravity should help the medicine go down.
How much is he on?? DD is on .23ml every 12 hours. But she's been complaining alot so i'm thinking about ringing her surgeon to see if she needs a bigger dose.

I feel your pain.