Vet News Comfortis and ivermectin: A confounding clash of the titans
By now, those of you with close ties to the veterinary profession may already know: Comfortis (spinosad) and whopping doses of ivermectin do not go hand in hand.
Comfortis is the new-generation, super-effective, oral flea killer I’ve been using on my most flea-allergic and flea-infested patients. At this point I’ve got quite a cache of Miami-area canines sucking spinosad fumes with apparent gusto (as in, Comfortis works…it works really well).
Perhaps that’s why I received a flurry of emails and faxes on Friday (June 26th, 2008) informing me of the news: DO NOT USE COMFORTIS ON DOGS RECEIVING IVERMECTIN!
Of course this raised an alarm, not least because I’d already been informed of the potential for negative interaction of these insecticides (spinosad and ivermectin)—and I’d been assured of Comfortis’s safety when administered with the labeled doses of ivermectin veterinarians currently use on a monthly basis for heartworm prevention (in Heartgard, Iverhart, etc.).
So I checked my emails, shuffled the faxes and quickly came to the conclusion that the FDA’s warning related to the large, extra-label doses of ivermectin used for the killing of mites like demodectic (red) mange, sarcoptic mange and, in some cases, ear mites.
Heartgard, Iverhart (and the like) used in labeled doses for the prevention of heartworms and other parasites? Not a problem. No reactions noted.
Yet my inbox told another story: Scary, life-threatening reactions the likes of which threaten the lifeblood of a product I currently find incredibly useful…when used with common sense, intelligence and, above all, prudence.
After all, what kind of vet layers parasiticides with nary a thought to their interaction?
Of course, I appreciate the news. I think it’s important to point out the obvious when the obvious may be elusive to some. But to question the safety of an apparently safe product (Comfortis) when used with unapproved doses of a product (ivermectin) whose safety margin is de-facto in question, is NOT the spin on this breaking news Comfortis deserves.
(And, NO, I DO NOT receive a lifetime supply of Lilly’s Comfortis for saying so.)
June 29th, 2008
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Add Comment20 Comments
The main reason I forwarded this news to people was that - at least here in Texas - I know a LOT of large dog owners who give liquid Ivermectin orally on a monthly basis for heartworm prevention. Which is fine, but in virtually all cases they are administering an overdose, and in many cases it's by a factor of 10 or more. I have the calculations for determining the dose by weight for dogs, and they aren't that difficult. But a lot of people have told me that they've been giving X amount for years with "no problem" and they don't want to change.
THOSE are the people I wanted to alert.
I'm with you, I hope this doesn't scare people away from Comfortis if their dogs need it.
Barb June 29th, 2008 01:35:00 PM
I'm in central FL in a rural area and it is quite common here for folks to give straight ivomec as hw preventive, and they give it in a dosage so that it will serve as an all purpose wormer. Ivomec is available OTC and I doubt anybody asks these folks about it when they buy flea products. I realize it's off label, but it is commonly done here. This will kill a lot of dogs.
Mary June 29th, 2008 03:14:00 PM
Barb: Your forward appropriately referenced the official Lilly document. Thanks for that. No complaints. Sorry if you felt singled out--didn't mean it.
And Mary: Great point. I didn't consider that. In my area the "offenders" are "horse people." They give huge doses of ivermectin as a dewormer and six-month heartworm catch-all. The emails and faxes were probably also aimed at alerting us to question the owners of these pets before prescribing Comfortis. Lots of times I don't think to ask this kind of question since mine is a 95% suburban practice. I stand corrected.
Dr. Patty Khuly June 30th, 2008 07:55:00 AM
Well, as a long time collie owner, I know the dangers of ivermectin. In collie land, responsible owners get their collies tested for the MDR1 gene (it's defect in chemical transportation across the blood-brain barrier and some drugs - Ivermectin in particular - get "stuck" on the wrong (brain) side of the barrier. I'm not a vet so I'm probably explaining it poorly. To get the straight story go to http://www.vetmed.wsu.edu/depts-vcpl/ ).
Many breeds can handle an overdose of ivermectin but give the same to a mutant/mutant or mutant/normal collie and it'll be dead or neurologically impaired. The problem is that while the MDR1 gene is mainly know in the collie (75% of the breed carry the mutation) , a number of other breeds (Shelties, Border Collies, GSDs, Aussies, long haired whippets) also have the mutation but in lower numbers.
Of the dogs that had bad side effects from Comfortis I would be curious about what breeds (or mixes) they were and their MDR1 status.
Chris June 30th, 2008 10:15:00 AM
Not to diminish the importance of the topic, I don't use or plan on use of either product. Just wanted to comment on the great picture!! Reminds me of the one I've seen with a Scottish Terrier nose to nose with a deer. Scottie standard "...alert & spirited, but also stable and steady-going..."
Barbara A. Albright/New Hampshire June 30th, 2008 04:49:00 PM
To Barb:
In your 6/29/08 post you mentioned that you had the calculations for determining the dose by weight for administering ivermection (ivomec) to dogs.
Will you please share it with us?
Thanks!
Nancy Taylor July 16th, 2008 09:53:00 PM
I HOPE TO USE COMFORTIS IN THE NEAR FUTURE IN MY KENNEL. HOWEVER I USE IVERMECTIN FOR HEARTWORM AT A DOSE OF .10 CC PER 10 LBS. I WOULD LIKE TO KNOW IF THAT IS SAFE WHEN USING COMFORTIS.
bonnie July 25th, 2008 01:05:00 PM
Our Lab is on HeartGuard and Comfortis and has been demonstrating excessive thirst since being on the combination for the last 3 months - we are concerned so we are stopping the Comfortis.
K Guth August 13th, 2008 08:24:00 PM
I started giving my chachawa comfortis about three months ago,now I wish I'd never given it to her. She was healthy,had no problems at all,now she is having breathing problems and I think she's tring to have seziers.NO MORE COMFORTIS FOR ANY OF MY DOGS,I SURE DONT WANT TO LOSE MY BABY,SHE JUST TURNED ONE AND I'M VERY UPSET.NOT BECAUSE I PAID 450 DOLLARS FOR HER BUT IT BREAKS MY HEART TO SEE THIS HAPPENING TO HER!!!!!!!
Barbara March 23rd, 2009 09:01:37 PM
My 8 mo. old poodle just had a reaction to ivermectin an comfortis. She was in a toxic situation and it was touch and go for a couple of days. She's doing well now. Be careful with this combination, please!!
Sandy May 27th, 2009 10:58:45 PM
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hood July 24th, 2009 08:29:35 AM
This will kill a lot of dogs. :(
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Jewelry Man July 27th, 2009 05:09:40 AM
What are your thoughts on Sentinal and Comfortis with Frenchies?
Kristine July 29th, 2009 03:58:21 PM
know a LOT of large dog owners who give liquid Ivermectin orally on a monthly basis for heartworm prevention. Which is fine, but in virtually all cases they are administering an overdose, and in many cases it's by a factor of 10 or more. I have the calculations for determining the dose by weight for dogs, and they aren't that difficult.
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Thanks for the information
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