Have Cat Questions? Ask a Cat Vet Online.
All cats should be on a monthly heartworm preventative. These preventatives are given once per month and contain the meds that will also take care of roundworms, hookworms, etc.
If you don't currently have your cat on a heartworm preventative, your vet can help you to choose a product.
Let me know if you still have questions.
I would not use any product made by Hartz for worms. They have some great soaps and things but flea and tick prevention and wormers from them are not a good idea.
Did I read your question wrong? If so, I would be happy to discuss this more with you.
If you are looking for a good once a month wormer, you should see your vet and get the pet started on a heartworm preventative that will ALSO take care of hookworms, roundworms, whip worms, etc.