As has been mentioned, forget the dry food.
Feed small canned portions, warmed up. Cats with poor appetie just seem to be overwhelmed with large portions.
So, offer no more than a tablespoon of canned food at a time. Warm it slightly by either adding a little warm water to it (good for the kidneys!) or sitting the dish in another dish of hot water, to wamr the food gently.
Warming the food makes it smellier, and that's what cats go by, smell.
Offer the small portion. If he eats it, but leaves some, pick it up, stir it around and bring it to whereever he has moved to, and offer it again.
Do this every few hours throughout the day. Cats of his age and health can feel even sicker if they go too long with out food, making them even more reluctant to eat.
I am deeply concerned that your vet has prescribed metacam for a cat with kidney failure. Metacam is not safe for cats anyway, it is known to cause acute kidney failure in cats. I advise you to research this, and to question your vet closely, and ask for something else, if your cat needs pain medication.