My DD is on zantac and she hates it!! I know it sounds mean, but I drop a little on DD's tongue to make her get all upset and start crying, then I squirt it down the back of her throat in bits so she has to swallow it!
I used to put the syringe right at the back of her mouth on the cheek but she would spit it back out. It is nasty tasting stuff!!!
Try giving it in little bits not all at once?