((
High Voltage))
It can be difficult to get medication into pets.
First off, I would ask your vet if there is any other way of delivering the medication (I imagine for antacids oral medication is necessary, but something in pill or capsule form, if such a thing is available, may be easier to administer than a liquid), I have always found my vet very helpful when it comes to working out the best way to get meds into a pet with minimum stress, and every pet is different.
Glad to hear that he is now eating again, if he refuses to eat for more than 24 hours then phone the vet for advice as stopping eating for longer than that can be serious especially if he already has some medical issues. Anorexia can a symptom of kidney issues, but needs to be treated asap before there is further impact on the organs.
If you have to forcibly pill him, keep in the forefront of your mind that it is for the good of his health and needs to be done, and usually the best way to do it is firmly and quickly. Often the easiest way is once you have hold of him, kneel on the floor with your knees apart and place him between your knees facing away from you (cats usually try to go backwards when something they don't like is messing with their face, so this prevents the reverse-maneouver escape) with one hand holding his scruff. Hold the pill between 2 fingers of the other hand with your palm holding his head tilted slightly up, and slip your thumb in the side of his mouth between the molars to open his mouth, then put the pill on the back of his tongue.
The method for forcibly administering liquid medication orally is slightly different but can be done in the same handling position, just use a small syringe without a needle (your vet can provide one a suitable size for the dose) and put the syringe in the mouth between the molars once you have opened the mouth. THE IMPORTANT DIFFERENCE WITH GIVING A LIQUID (sorry to shout, but it is important!) is that you do not put it at the back of the tongue or angle the syringe towards their throat because you don't want them to choke on it or inhale it into their lungs, you do it across the tongue and slowly. If in doubt, ask your vet or a veterinary nurse to show you how. This usually gets it over and done with quicker than buggering about with their food trying to hide the meds.
That image comes from
http://www.wikihow.com/Give-Cats-Liquid-Medicine which gives excellent step by step instructions.
(EDIT: I would add "wear a longsleeve sweatshirt" to the list of instructions just in case, Jakey hates the carrier and although he is normally a gentle creature and it was in no way malicious, he panicked when I was putting him in the carrier to take him to have his tumour removed and my arms got a bit shredded as I was wearing a short-sleeved t-shirt. Long sleeves always a good idea when handling pets for something necessary that they may not enjoy).