It was good of you to post. You never know when someone might be reading these old threads. The warning is always timely.
And it illustrates what others in this thread have said, no matter who says what on the internet, it is never safe to use an OTC medicine on your cat unless the attending vet has prescribed it.
Has the vet tested for Tapeworm? Slippery elm is for diarrhea. That is what I give. I also boil a chicken. In a small cat bowl put one soup ladel of the chicken broth in the bowl, one tablespoon of pumpking. Not the pie filling type, but pure canned pumpkin. Let cool and serve. They will drink it. Make sure not to add any ingredients when you boil the chicken. Keep the rest of the chicken liquid in fridge. Use as needed. Slippery Elm from a health food store helps. My kitten just love the chicken broth with the pumpkin mixed in. And they were only 12 wks old when the tapeworm was discovered. I rescued them from under my house when the mother abandoned them. They were full of fleas, had ringworm added on top of the other problems. I had to bottle raise them, deal with the ringworm (use Fung-A-Way at Tractor Supply Co.). Also mixed some Acidophilus (available in Vitamin section at Walmart) in with a bit of broth. I have a coffee grinder that, if they are tablet form, I can grind them up. Then mix 1/2 teaspoon with 1 tablespoon of chicken broth, and feed with an eye droper. This will replace the good bacteria in their stomach. Any time they are sick, or on antibiotics, the good bacteria is killed off. That needs to be replaced. Vets understand that many people can not afford a vet, and that is why shelters are full. But sick animals are always euthenized at shelters. So you have to research online, and do your best. My furbabies all recovered. Took a while for the ringworm to go away. But hang in there. It will get better. I am a retired Vet Asst.