wormer for cats

Question
Hi Jessica,
just came across one of your questions thru googling, and read your expertise and have a question about a wormer called piperazine. Just for your bakground, I also rescue, spay/neuter, adopt-but mostly keep my cats, and have about 60 now I care for daily.  Have used the vet in the past for worming, but could not afford it now and arecently purchased an item: "D-Worm" by Farnum Labs, the active ingredient is "dipiperazine sulfate".  Had never used it before.  Gave my little guy--about 6 months old, I had him for about two months, was healthy and beautiful-- the correct dosage.  He vomited roundworms, and I though this was okay--I didn't know.  He continued vomiting clear and yellow fluid, and died a few hours later.  He just stopped breathing.  Besides being devasted I was trying to think of what could have caused his death?  But he did not seem sick to me at all.  A few days later, I  spoke to a women in a NJ rescue organization who has cared for hundreds of cats, and when I told her about the wormer, she immediately told me what happened.  She said this has happened to her, and that this product should not be on the market, because it has killed many cats, it is appareantly too strong and brings the parasites up to fast.
First, I wanted to simply pass this information on to you--I am so upset and I know this substance killed my cat.  Second, I wanted to know if you have any experience with this product?
There is a similar product on the market called Crazy Little CatWormer, but the piperazine in that one is "piperazine citrate" according to the dosage chart, itis not as strong as the "D-Worm".
I just am so devasted because I never thought a product I could buy in a pet store would be that strong, I thought it may not even work.  People should be made aware of the danger of this product.  I lost a precious beautiful cat because of it.

Answer
Amy, that's so awful!  I'm so sorry to hear that.  There are many products on the market that definitely should not be there.  

I have used dipiperazine sulfate, and this is the first I've heard anything negative about it.  I used piperazine citrate once, and it was as you and I would have suspected - didn't work.  So I only use and recommend pyrantel pamoate, the ingredient in Srongid, which is what I find is prescribed most often for cats.  The information you just gave me gives me all the more reason to recommend pyrantel pamoate only.  I will definitely keep this information in mind and pass along warnings to all I know.