VetriScience Kidney Health Powder, Renal Essentials Supplement for Cats, Kidney Care and Support with Mushroom, Astragalus Root, Nettle Seed and Herbs, Chicken & Cheese, 60 Scoops

FWIW, I work in formulation of exactly this kind of stuff and took a look at the ingredients. Can you clarify if he is on liquid GABA or is it actually gabapentin? Either way, I don't suggest mixing them. It can cause a whole host of problems or side effects that can obscure his symptoms and aggravate others. Kidney stones (calcium oxalate) do not dissolve. If you are looking to support kidney health: A supplement like VetriScience Kidney Health Powder (not the tablets) or Fera Pets Kidney are excellent and the ingredients are nutraceuticals that are formulated with the help of veterinarians and there are genuine studies that back the efficacy of the ingredients. Both brands are using very similar formulations. Both are great. The Fera Pets product has probiotic in it, which is helpful. Hopefully you will be able to get a refund on the drops you purchased.