Cats and humans have very different digestive systems, and it's generally not advised to administer human medication to pets; I would extend this caution to supplements, which are not only geared toward human digestive systems, but loosely regulated.
I would recommend consulting with your vet before starting any species-appropriate supplement, as your cat is already on medication; while it's unlikely that adding a probiotic would cause any serious issues, the vet should still be part of medical decisions like this one. He or she may also be able to recommend a brand or two of probiotics to you.
In a brief review of listings for probiotics for cats on Amazon, the cultures used are:
*Enterococcus faecium (2 products)
*Lactobacillus acidophilus (3 products)
Only the first four (starred items) are present in brands that my vets have recommended to me over the years; while there is some overlap, the sugars and starches included in your human probiotics are not present. (Excluded from my list were some supplements that bragged about the number of strains; this is more marketing than useful and I would not recommend these brands.)
Additionally, feline probiotics come in powder form, not pill form, with an appealing scent and flavor, making them extremely easy to administer. These features also make them a benefit with ill cats who may be resisting eating in general, as the stronger smell and taste of the food can help with a cat who may have a slightly dulled sense of smell or taste.