For Caitlin

Hey there. Your site is the only site I could find that mentioned the dosage of selamectin (others just give a disclaimer about Revolution medicine). You wrote that you need about 10 times as much medicine to kill intestinal parasites as you need to cure them. I have had a few unproductive vet experiences… so I am looking for some other help. So, here’s my situation:

I recently administered topical selamectin to my two cats. One cat, Simone, has had serious parasitic issues (once throwing up a fairly large roundworm). She had a serious brush with liver failure (cause still sort of unknown), so we waited to do a heavy-duty treatment of parasites. I used some herbal things in food for a while after the threat of hurting her seemed to have faded, and just sort of hoped they had been taken care of.

Enter 2nd cat- friend’s lifelong indoor cat. Lives with us harmoniously for a while, begins dragging itchy butt on carpet… shows a few signs of parasites…

We called the vet and asked for the best broad spectrum dewormer- didn’t want to try herbs again. The cats were prescribed topical selamectin. We dose them both with a ‘one month’ application. Only immediate side effects are a little drowsiness – that sort of thing. But then their poop started to smell unbelievably bad. Stinking up our whole flat. And this has continued for a week. Also, the butt dragging has returned.

How long do you think it would take for selamectin to work in a small animal like a cat?
Did we give them enough to kill roundworms?
Any ways to know if it’s working?

First and VERY IMPORTANT: I AM NOT A VET. Any time you feel that you are in an emergency situation or an animal is genuinely ill, do not take advice from the Internet. Go to a vet.

Second, just to clarify: my statement was that you need to use about 10x the dose of ivermectin to kill intestinal parasites as you do to kill heartworm larvae (which are substantially easier to kill than intestinal worms). This means that the selamectin given on the neck is a higher dose than would be circulating in the bloodstream if you gave a dog Heartgard. That’s why I don’t like Revolution as a routine wormer or a flea/tick med. That’s as proscriptive as I get. Revolution has its place and it’s a valuable medication; I just don’t like it being used if the dog doesn’t need the hit-a-pin-with-a-sledgehammer approach.

Having said those two things, let’s look at your situation. You have a cat with a demonstrated roundworm problem. You have two cats who are dragging their bottoms.

You gave them both Revolution, which does, very effectively, kill roundworms and hookworms and so on. If they had heavy roundworm infestations, the Revolution killed them all off and their bodies are passing them now, which I suspect is the cause of the bad smell. There is very little doubt that you DID give them enough medication to kill the roundworms and any hookworms too.

Where you may NOT have cured things is if the bottom-dragging is because of the itchiness caused by TAPEWORM. Tapeworm does cause some cats and dogs to feel itchy, and it is not cured with Revolution. It requires a specialized medication called praziquantel. You can get this from your vet or, in many areas, over the counter. I am not sure where you are in the world, so I don’t want to guarantee it for your area.

If you’ve ever had fleas on either cat, I would strongly suspect tapeworm and use that medication in about a week, after the Revolution has had a chance to do its job. If you’ve never seen a flea, ever, and the cats continue this behavior, I would take in a fecal sample, again in about a week, and have the vet check for any parasites that may still be left.

I hope this helps, and that they recover quickly and thrive 🙂


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