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ADE reports, advantix, adverse drug experiences, allergies, bad reactions, Center for Veterinary Medicine, comfortis, drug reactions, drugs, elanco, FDA, flea allergies, flea dermatitis, flea preventatives, fleas, frontline, milbemycin oxime, spinosad, trifexis, veterinary medicine
When Bowdu was battling his summer of extreme allergies, I became adamant about the need for continuous flea control. In the past, we’d used monthly topicals with apparent success. It was difficult to see any bugs camping out in Bowdu’s thick fur forest anyway. But in the process of trying to deal with his allergies and improve his skin condition after his hypothyroidism diagnosis, our vet — a new one to us, at the time — recommended that we bathe Bowdu a little more frequently during allergic months, and give him an oral flea preventative to complement that measure. She recommended Comfortis (spinosad), which we’d never tried or heard of before from any of our previous vets. We started using it in October 2010 and have been satisfied with its effectiveness.
There are several disadvantages to spot-on topical flea treatments like Advantix and Frontline. The application process itself isn’t an issue, but I never liked the smell — and if I dislike it, I can only imagine how the lingering scent assaulted Bowdu’s sensitive nose. They leave an unnatural residue, I couldn’t bathe let alone touch the dogs for days after application, and even when instructions were followed to the letter, fleas seemed to return well before a whole month had lapsed… as we found out when we got Bowpi, whose short fur made them easier to detect.
The Bows are active, outdoorsy, and relatively social. If we do nothing, they will pick up fleas, and the last thing we need is an infestation in the house. So it’s critical for me to keep them on some kind of flea preventative — Bowdu in particular, as I fear that a single bite could trigger an itch that would cascade into another summer of dermatitis hell.
So Bowdu gets his flea meds pretty much every month here in the California Bay Area, the land of eternal spring. Fleas never seem to go dormant here, and I’d rather Bowdu be on prevention than deal with the aftereffects. I am more conservative dosing Bowpi for a number of reasons.
For one thing, she really hates the taste. Comfortis claims their product is a “chewable, flavored tablet” that is “readily consumed by dogs.” If it tastes like it smells, it must be rich with the flavor of… medicine. Blechk. We learned just how adept Bowpi can be at spitting out pills because of this drug, which she will NOT ingest unless it’s split up and well hidden in a flavorful, sticky meal. Since you’re supposed to administer this with food, luckily this is not a huge issue.
Secondly, Bowpi’s short fur makes it not only makes it easier to find, but also to eliminate fleas by hand. I’ll often let her go without the drug until I do happen to see a bug. Then I snatch it off her white belly or wherever, she gets medded at next meal, and the problem is quickly resolved. It is startlingly fast and effective; one time, I just happened to find a dead flea on her two hours after dosing her. The package claims that one dose will start killing fleas in 30 minutes, and it remains effective for an entire month. I do not exactly understand the internal mechanism by which the drug spinosad works, but it’s obviously potent!
The main reason I take it easy with Bowpi is because of her weight. She ideally hovers around 20 pounds, give or take half a pound. But the first time my vet sold us the drug, she automatically prescribed the same dosage for Bowpi as 30-pound Bowdu. This makes it easier for us to just buy one box specified for dogs 20.1 ~ 40 pounds that we can give to either dog as necessary, instead of having to purchase two separate boxes.
HOWEVER, I do not give either dogs a full pill. I generally break each tablet into four quarters as evenly as possible, and give Bowpi the equivalent of half a pill while Bowdu gets three-quarters.
I do this for a couple reasons. Elanco’s product label for Comfortis states that the 10.1 ~ 20 pound dosage contains 270 mg of Spinosad per tablet. The 20.1 ~ 40 pound contains 560 mg of Spinosad per tablet, or just a little more than double the amount of drug in the previous weight range.
Recommended minimum dosage for the drug to be effective is 13.5 mg/pound — so each dose actually contains just a little more than this baseline amount for the top end of the weight range to ensure the drug’s effectiveness. Bowpi for example, if at a full 21 pounds, would need at least 283.5 mg (50.6% of a pill) and Bowdu at 30 pounds needs at least 405 mg (72.3%). The drugmakers expect the dogs to be able to tolerate some overage, and indeed, my dogs never seemed to have any problems the two times I gave them the full pill.
Unfortunately, many others do. I first noticed an alarming number of online reports of negative reactions to Comfortis collected in the comments section of an entry by Dr. Patty Khuly dated March 29, 2008 on Fully Vetted, Comfortis, the flea-killing wonder drug, and the general state of flea drug resistance. It was introduced to veterinary use that year, and Dr. Khuly was singing its praises. The comments piling up under that post, however, seemed overwhelmingly negative — now at 139 comments at the time of this post and still accumulating, including the top voted comment about a Shiba Inu’s bad reaction. I have seen no followup on Fully Vetted or on Dr. Khuly’s new blog at VetStreet.
And then I started noticing handfuls of Shiba and Basenji people on my breed-specific forums reporting and asking about bad reactions to Comfortis and its sister drug, Trifexis (which contains both spinosad and milbemycin oxime for heartworm prevention). I got curious and asked about specific weights and dosages, and noticed that everyone who reported issues had pets that weighed in the lower 20-something pounds, but were giving full pills for 20.1 ~ 40 pound dogs. In one case, a Shiba owner followed up with a call to the company hotline, and was told that her specific cluster of symptoms (laying in “contorted positions,” being unresponsive, trembling, having difficulty maintaining balance) had not been reported before.
Unfortunately, the company representative was flat-out wrong. The FDA has actually collected pages and pages of documented Adverse Drug Experiences for both Comfortis and Trifexis — cumulative reports available in .pdf form here (search by drug name, not product name). So make no mistake — it is a controlled substance, and no drug is “perfectly” safe, as the full document made apparent to me.
That said, my own dogs have not had any problems with it, especially not after I began minimizing and fine-tuning the dosage on my own. My own conclusion was not that the drug itself was inherently evil, but that it remains important to monitor my pets for their own, individual sensitivities. Because the Bows have not reacted badly, and for us, the benefits outweigh the [unseen, to us] risks, I do plan to continue using Comfortis. Nevertheless, knowing that my specific breeds (and of course, others) commonly fall in that lower 20-pound danger zone, where they seem most susceptible to the possibility of overdosing, I will continue to suggest splitting up the pills as a precaution. No, the drug is not “guaranteed” to be blended evenly throughout the pill, and it’s not scored for ease of division. But this works for me until Elanco decides to fine tune this particular dosage jump.
Note: a similar problem applies in the difference from 40.1 ~ 60 pounds (810 mg) and 60.1 ~ 120 pounds (1620 mg), but the change is most pronounced in the size upgrade I’ve been discussing.
In summary…
Comfortis PROS:
- Highly effective, fast-acting, consistent
- Leaves no smell or residue
- Lasts a whole month
- Allows pets to be bathed as necessary
- Relatively easy to administer with food, though picky pillers may need some tricks
Comfortis CONS:
- Noxious smell and taste may make it unpalatable to some dogs
- Must be prescribed by your vet
- More expensive than topical treatments (approx. $60/box for spot-ons vs. $90/box for a 6-pack of Comfortis)
- Does not take care of ticks
- Poor customer support from company (based on my own experiences in addition to anecdotal information above)
- Potential for adverse drug effects not fully acknowledged
Finally, if you do find that your pet has experienced an adverse reaction to this or any drug, please ask your vet to help you fill out an Adverse Drug Experience form to send to the FDA. Internet anecdotes and the advice of well-intentioned non-professionals such as myself should always be taken with caution. Ultimately, the relevant regulatory agencies also need to be notified through the appropriate channels.
Adverse Drug Experience form: http://www.fda.gov/AnimalVeterinary/SafetyHealth/ReportaProblem/ucm055305.htm
Comfortis website: https://www.comfortis.com/
Trifexis website: https://www.trifexis.com
Elanco Pet Health (makers of Comfortis and Trifexis): https://www.elanco.com/products-services/pet-health.aspx
Edited to add more relevant links to anecdotal information as I stumble across new info:
Trifexis Toxicity in Dogs: Charlie had a Scare!
The House of Two Bows 雙寶之屋 
I used to use Advantage, and both I and my pets always hated it. Once I started fostering dogs, it wasn’t feasible to dose all three cats and both dogs when one showed up at the door with fleas, so I started using food grade diatomaceous earth. I’m amazed at how effective it is. I just work a tablespoonful or so into the fur of all pets near the base of the tail, sprinkle a little on the bedding, and never see another live flea.
The fine particles stay put for a few days on the animals if you don’t pet them too vigorously (you can pat their butts and see little puffs of dust) and this seems to be long enough to kill them all. I now treat every new animal that comes in the house and we haven’t had an infestation for years. I even had one large foster dog come in totally covered with fleas and they were all decimated within days and didn’t travel to any of my other pets. Cheap, non-toxic and it really works!
Never tried food-grade DE before, but have heard others speak of it. Honestly, it sounds messy to me! But it is an alternative I keep in mind.
It’s really not, it tends to stay put and you don’t use much. After a few days it just sort of disappears. You just gotta really work it into the fur well. I’ll never go back to meds for flea control.
I’m trying to get ready for tick season here, hate them so much. A lot of people get guinea fowl to find and eat them, and they apparently do a great job, but I don’t really want a bunch of noisy guinea fowl. Or the discovery that one was munched by some predator, because I’m sure I’d get attached to them…sigh.
Neither Comfortis nor Trifexis takes care of ticks… but we’ve found surprisingly few in our years here, knock on wood. I’ve disposed of a grand total of two, with the second one being just last week on Bowdu. Boy, that was fun. Luckily that one wiggled right off with minor jostling and didn’t need tweezing!
This was interesting because Sparks has been on Trifexis since she was a puppy, and never had any scary side effects. She has thrown up on two separate occasions after taking her pill, but showed no other ill effects. Since we’ve started storing the pills in the freezer (at the vet’s recommendation – she said freezing the pills helps for some dogs) we’ve had no more trouble.
Part of our good experience may stem from the fact that Sparks is at the top of the weight range for her dosage – she weighs 18 lbs and takes the pills for 10-20 lb dogs. With all the stray cats and squirrels around here to host fleas, I need to keep Sparks on something, or the evil little creatures start showing up in a matter of days. I agree about the dermal treatments being unpleasant. We use Advantix occasionally when we’re going to be spending a lot of time in tick invested areas (like camping) but it’s so greasy and gross. I want to be able to pet my dog without immediately washing my hands.
Throwing up is definitely a side effect I’ve heard others mention… but luckily not so scary. None of the anecdotes I’ve personally heard of/read have been anywhere as scary as some of what was reported in that Fully Vetted post. My inability to pin down any kind of official response from Elanco makes me leery of the company’s intentions to rectify the problem IF one should arise for us.
I have used Comfortis, and currently use Trifexis for my three. Faolan was very sick the day after his November dose of Trifexis, vomited, lethargic, foul breath, but recovered quickly. It was a one time event, and I’m hopeful it remains that way.
My dogs will not willingly take chew tabs either. Neeko eats hers wrapped in cheese. I have to crush Bruce’s, and mix it with cottage cheese or canned food. I shove Faolan’s down his throat.
Most of the incidences I’ve heard of have been quick recoveries, luckily, with varying degrees of severity. Nothing as dramatic as what is reported on the Fully Vetted page. But I do get irritated by the lack of any official response from anyone whose authority on this would matter… none that I can find, anyway.
Very interesting about the dosage. I used Comfortis on Silas for a while, but I found that I just didn’t need it. On a short-haired white dog, it just wasn’t a big deal to find and destroy single fleas. Ticks, on the other hand…
The “palatable” flavor of Comfortis is beef, which may be why Bowpi won’t take it.
Looking at some of the drug information sites, that is a really interesting drug. It seems like it was startlingly well-tolerated in clinical trials, given the therapeutic dosage. For something that is as toxic to fleas as it is to be that thoroughly non-toxic to vertebrates is, well, I’m not an expert but it’s not something I’ve heard of before.
The LD50 was not discernible (> 5000 mg/kg). A study for long-term heath effects found that you needed a dosage of at least ~10 mg/kg per day for weeks to see any difference from control, and, as you point out, this stuff hangs around for a month, and so we’re talking about a LOT of the active ingredient over a long time in order to show symptoms. No carcinogenicity evident even then.
As for how it hangs around for so long, I had a lot of trouble finding that information, but it seems that a hint might be here:
An ADME study using radiolabelled 14C-spinosad in dogs showed that the parent compound accumulated in perirenal fat, skin/ fat and the liver, but the data indicate that this accumulation had markedly decreased 21 days after administration of the dose.
I’m not certain about this part, but it seems to imply to me that the compound is quite lipid-soluble, but not very water-soluble. It is absorbed by various fats in the body and then slowly excreted over the course of a month.
Interesting information, btw. Thanks for sharing! That’s scary and rather surprising about the LD50. I do often wonder how well the clinical version of “long term” effects maps onto real life usage…
Actually, I was looking into this stuff a little more and it’s absolutely fascinating. It targets a ‘nicotinic’ receptor site (which is a new term for me, but is more or less what it sounds like) that exists in the insect nervous system but not in the human one at all. This means that it can kill bugs at such tiny concentrations that more gross side effects in vertebrates are fairly unlikely. Which explains the LD50, and also how it can kill pests so effectively after only one dose, for an entire month.
It’s actually also approved as a pesticide. In fact, it’s one of the few pesticides that is approved for use on organic farms, since it is a natural fungal product. (However, very few organic farms, at least in California, use it or any other pesticide, and the ones that do generally only do so in response to a serious outbreak, less often than once every five years.) As you might imagine, there are almost no pesticides that are also approved as drugs for oral use, even for veterinary use.
Assuming that the clinical trials are accurate, and no major long-term side effects are found (and I am cautiously optimistic about that, given the data), this stuff is pretty amazing.
My holistic vet recommended Trifexis when I first got my corgi, Chubby. He’s been taking it for a year and a half now without any serious side effects. I have noticed that sometimes he would get lethargic after getting his monthly dose. The comments on the Fully Vetted blog are very unsettling.
Like Bowpi, Chubby is hovering a little over 20 pounds. I give him the full 20-40 lb. monthly dose because as mentioned the pill is not guaranteed to be blended evenly. However after reading the stories about dogs in the lower weight range who have reacted poorly, I think I might give him 3/5-3/4 of the pill so as not to overdose for his weight. I am worried about the possible long term effects to vial organs as Comfortis/Trifexis is a relatively new drug without long term clinical trial data.
BTW, great blog. I live in the SF Bay Area as well – my father works in Taipei so I visit often. I was always astounded and saddened by the number of strays wandering the streets and had no idea there was a place to volunteer to transport rescue dogs to CA! I will have to look into it and see if I can help next time I’m back in Taipei.
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So glad I found you! Bless your two doggies. I have two rescue dogs, one has been with me for just over two years and one came last week. Comfortis. Ah, the bane of my life. I use it on my girl and she and I both hate it – the smell, the immediate itching she gets . . but it works. The new dog is seriously underweight, so until I get him up to weight I am really worried about the Comfortis dosage. I get the 18.1 to 27 kilo tablet as the girl is 21kg and the vet recommended this size. The new boy is much bigger than her, but is nearly a kilo less in weight, therefore I am seriously considering cutting the tablet in half as they are both so close to the low range weight. Also, even though the new boy is well and has had my vet check him out, I see him as debilitated due to his weight. I am terrified I might make him sick and I really appreciate that you have worked out a way to divide it up for your dogs. Thank you to all the folks here who have shared here – it has really helped to ease my mind – I was seriously going to stop giving Comfortis due to all the bad publicity. If half a tablet still works, I think I will stick to it. It is so upsetting to think we could be harming our beautiful dogs by giving what we have been led to believe is a safe treatment.