Do you know what kind of worms your cat has? Is it tapeworm?
White tape like strings on the back end. Roundworm?
Black Walnut can be used to effectively treat tapeworm but should be used with caution. ( Tilford). You should be able to find it in a glycerite if you don't want to use a tincture.
Avena Botaincals sells a deworming vinegar for roundworms and tapeworm. Their site is www.avenaherbs.com
. I haven't had an opportunity to try it yet but looks interesting. Contains sothernwood , rue, aloe vera, black walnut and garlic. You would need to check to see if the herbs are safe to use in a cat with kidney concerns. They also give dietary suggestions and other facts.
Anything you give wether medicne or herbs is going to be strong because of the purging action. The pill the vets use is cestax and works within 24 hours. I imagine the herbs will take longer to work. From what I've read you would need to follow the protcol for almost a month.
Here goes my 2 cents... From a quality of life issue...if your cat has a weak system.. is it easier on the cat to take a pill and be done it with it realitively fast , possibly less stress on the body or go with natural remedies that take longer and may harder on your cats system. I don't know, just sharing some thoughts. Let us know what you find.
Good luck. Blessings to you and your kitty,