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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.

Dips and rises

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!

What are you doing? This is not a topical...

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.

Stinky Comfortis

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!