metronidazole is an antibiotic, so if your vet gave it he probably suspects Banksy has an infection. Does he have pancreatitis by any chance? I would definitely not skip the antibiotics. Here we have a "sandwich paste" with a bit of liver in it that cats usually adore, so it's a good thing to slip small pills in. Metronidazole tastes nasty though, hence the syringes, rather than pills, maybe? You might want to check with your vet if there is an alternative. Does your vet know you have trouble giving him his medication?
Also, have you tried pilling him? There are a bunch of videos on youtube that show various techniques. The main advice I give for pilling a cat is to "distract before, distract after". Make the pilling "proper" part of a wider and largely pleasant routine. Example: scratch under chin, pet on head, basically "pet" his head into the right position (chin up) and then quickly hold, open jaw, slip pill into throat (that takes about half a second), and then continue the scratching and petting (reward).
You need to practice this in stages and try to stop before getting "resistance" from the cat. First you just scratch and pet and then "grab" his head for half a sec, and let go, and continue petting. It's clearly not ideal to start doing this when you actually have pills to give him, but you can still do it: if your time allows, do this a dozen times a day when you're not giving meds. Like that the cat will not associate this "routine" to systematically having a finger and nasty pill shoved down his throat. It'll be "hmmm, nice petting, hrm, sometimes they do something that's not so pleasant but the petting continues, I can put up with that..." See the logic?
