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Dr.Fiona, Cat Veterinarian
Category: Cat
Satisfied Customers: 6273
Experience:  16 years experience as a companion animal veterinarian in British Columbia, California and Ontario
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I think I gave my cat to much Excel Roundwordworm De-Wormer

Resolved Question:

I think I gave my cat to much "Excel Roundwordworm De-Wormer" he's vomiting. What should I do?
Submitted: 8 years ago.
Category: Cat
Expert:  Dr.Fiona replied 8 years ago.
Hi thereCustomer

Welcome to Just Answer! I would like to help you and your cat with this question, but need a bit more information in order to better assist you.

When did you give your cat this product? (is this the one:

How much did you give?

How much does he weigh?

When did he start to vomit?

Customer: replied 8 years ago.
We gave it to him around 4:30 pm, the name on the box reads Excel roundworm De-wormer. It said to give 1 tablet per 4lbs of his weight. He weighs approx 15-18lbs. I gave him 3 1/2 tablets. He started to vomit about 2 hours after he took the medication (I think)
Expert:  Dr.Fiona replied 8 years ago.
What time is it where you are?
Customer: replied 8 years ago.
9:30 p.m. (it was aprox. 4:30 p.m. when he took medicine)
Expert:  Dr.Fiona replied 8 years ago.
Ok - so 5 hours ago.

And can you confirm that EACH tablet contains 100 mg Piperazine and you gave 3.5 tablets?

This information should be on the side of the box, under ACTIVE INGREDIENTS.
Customer: replied 8 years ago.
100 Mg. Piperazine Dihydrochloride, is correct. 5 hours is approx. and it was 3.5 tablets given
Expert:  Dr.Fiona replied 8 years ago.
Ok - working on your answer, be right back!

How many times has he vomited, and what was in it?

Any diarrhea?

Any drooling?

Any muscle twitching?

Any difficulty breathing?
Customer: replied 8 years ago.

Total of 4 times....1 big amt that contained hair, 3 smaller ones that had his treats and his food in them. The first time he vomited was considerably runny. Almost a greyish brown color. The others were the color of his food and treats. No diarrhea, No drooling, no muscle twitching, No difficulty breathing either, however his nose is quite warm and he's not moving around as peppy as prior to medicating. He's purring loud as usual but wants to hide and lay down.

Expert:  Dr.Fiona replied 8 years ago.
Hi again,

The dose of piperazine that you gave you your cat is well within the normally prescribed dose. So, you did not overdose him.

You can see more about this dewormer here:

Now, even though he was dosed appropriately, it is worth mentioning that sensitive animals can have side effects even at low doses.

I will quote here from Plumb's Veterinary Drug Handbook 5th Edition (the most widely used and respected drug reference guide for vets):


Adverse Effects/Warnings
Adverse effects are uncommon at recommended doses, but diarrhea, emesis and ataxia may be noted in dogs or cats.

Acute massive overdosage can lead to paralysis and death, but the drug is generally considered to have a wide margin of safety. The oral LD50 of piperazine adipate in mice is 11.4 g/kg.

In cats, adverse effects occur within 24 hours after a toxic dose is ingested. Emesis, weakness, dyspnea, muscular fasciculations of ears, whiskers, tail and eyes, rear limb ataxia, hypersalivation, depression, dehydration, head-pressing, positional nystagmus and slowed pupillary responses have all been described after a toxic ingestion. Many of these effects may also be seen in dogs after toxic piperazine ingestions.

Treatment is symptomatic and supportive. If ingestion was recent, use of activated charcoal and a cathartic has been suggested. Intravenous fluid therapy and keeping the animal in a quiet, dark place is also recommended. Recovery generally takes place within 3-4 days.


So, it is quite likely that it was indeed the dewormer that caused him to vomit, but not because of anything you did wrong. It is quite likely that your cat is simply sensitive to this.

So, what can you do to help him?

I would suggest the following if he were my patient:

1. Remove his food overnight.

2. Offer SMALL frequent amounts of clear fluids. So, this would be about 1 teaspoon every 15minutes (thus a total of 4 teaspoons, or 20mLs per hour).

Water is fine, but also you can offer small amounts of these fluids diluted 50:50 with water:
- water from a can of tuna
- onion free chicken broth
- onion free beef broth
- clam juice
- water from a can of turkey/chicken/ham flakes

3. Tomorrow, offer him small amounts of food (about 1 tablespoon) every hour.

If he cannot keep the fluids down, develops muscle tremours or difficulty breathing, or is getting worse in any way, then I do think you should see a veterinarian tonight. If he stops vomiting and keeps the fluids down, then that is encouraging.

I would recommend that you see your veterinarian if you need dewormers for this kitty as your vet will have safer options. He seems like a sensitive cat!

If this has been helpful, please accept my answer and leave feedback.

If you need more information, just click on reply and I will be back to provide it!

The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.

Best wishes to you and your boy!

Dr.Fiona and 2 other Cat Specialists are ready to help you