Sentinel vs. Trifexis: Which All-in-One Preventive Is Best for Your Pet?

Which heartworm preventative is right for your dog?

If you’re like most pet owners, you want to provide your pet with the best protection from parasites with the least risk, hassle (for you and your pet), and cost. To help you decide which all-in-one preventive is best for you, we’ve put together a comparison of two major all-in-ones: Sentinel and Trifexis.

Similarities between Sentinel and Trifexis

Both Sentinel and Trifexis:

  • Contain the active ingredient Milbemycin Oxime, so they both treat and control roundworms, hookworms, and whipworms and protect against heartworms
  • Are chewable tablets that should be given once a month
  • Require a prescription from your veterinarian
  • Can be purchased online at 1-800-PetMeds

Differences between Sentinel and Trifexis

  • Cost
    One dose of Sentinel costs about $5 less than one dose of Trifexis.
  • Age at which each can be administered
    Sentinel can be given to puppies at beginning at 4 weeks; Trifexis can be given to puppies beginning at 8 weeks.
  • Minimum weight requirements
    Sentinel can be given to dogs as small as 2 pounds; Trifexis can be given to dogs as small as 5 pounds.
  • Flea control properties
    Sentinel contains Lufenuron, which prevents flea egg development and ends the flea life cycle, but doesn’t kill adult fleas; Trifexis contains Spinosad, which kills fleas (it has been proven to kill 100% of all biting fleas within four hours).
  • Cautions
    You should be cautious when giving any medication to your pet. And make sure you mention any other prescription medications or supplements you’ve given your pet to your veterinarian so he or she can check for drug interactions. Both have the potential for drug interactions. Trifexis carries the following caution: “Serious adverse reactions have been reported following concomitant extra-label use of ivermectin with spinosad alone, one of the components of Trifexis chewable tablets.”
  • Side effects
    With Sentinel, side effects are rare, but they can occur and may include vomiting; Trifexis may cause vomiting, and other side effects are less likely but possible.
  • Customer reviews
    Sentinel has a 4.4-star rating average from online shoppers and Trifexis has a 3.7-star rating average from customers.

We hope that this comparison has helped you decide which all-in-one preventive is right for you. Once you’ve decided, we hope you’ll visit 1-800-PetMeds for all of your pet supplies. Happy shopping!

Update 11/13/2013:  According to the FDA and Eli Lilly, Trifexis is safe and effective when used according to label instructions.  Unfortunately a small percentage of dogs may experience adverse reactions when taking this or any medication.  We encourage pet owners to consult their veterinarian before administering Trifexis or any other medication to their pets.

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  1. Gave It to my healthy 7 mo old Rhodesian Ridgeback dog. In under 2 hours later he was dead. I was told there was most likely an underlying condition. So we had a licensed pathologist perform a necropsy and guess what? There was no underlying condition. To quote the report directly.
    “We can confirm that there were no preexisting conditions that could be detected either grossly
    or microscopically.”
    All I know is this was my experience. My dog was fine he took the medication and then he died. They can’t find any cause so draw your own conclusion

  2. Hi Sarah,

    I’m so sorry for your loss! The loss of a pet is hard enough, but to lose one so young and suddenly is tragic. Just for clarification, can you please let me know which medication gave your dog – Sentinel or Trifexis?

    Warm Regards,

  3. I’m sorry you lost your dog, but you need to be specific and name the product when you’re making allegations about it killing your dog. This article is comparing 2 different products so we don’t know which one you used. I recently read some negative things about Trifexis that could be in line with what happened to you, but I’ve been using it for my dogs for years and never had a problem.

  4. I have used Trifexis on my shelties for six years with no problems. Was just wondering if Sentinel works just as well at a lower price. It looks like the flea control might be a problem with Sentinel, if it doesn’t actually kill adult fleas. Can anyone out there make a comparison from experience?

  5. I use Trifexis, no problems so far. I have a 6 month old Standard Schnauzer and he’s used it twice so far. I do believe he vomited the second time, but not sure because I made the mistake of giving it to him before I left for work. As well he had apple pieces for the second time that day, so I’m not sure which caused the apple upchuck. Like everyone else, I am curious about which of the 2 meds the Rhodesian was using before his tragic demise.

  6. Trifexis and Sentinel are now owned by the same company, Eli Lilly. Novartis who was the original manufacture of “Sentinel” (a heartwarm drug with a much safer track record than Trifexis) had their Animal Health business bought out by Eli Lilly (the manufacture of Trifexis) and Company for approximately USD 5.4 billion in Jan 2015. (Source:

    A formal complaint was made to the FTC:

    FDA review on Trifexis can be found here:!documentDetail;D=FDA-2011-N-0003-0005

  7. Which did you use?

  8. I have two healthy dogs and used the Trifexis which never caused negative side effects to my knowledge. I switched to Sentinel because it seemed like a better deal. Boy, was I wrong. Both dogs immediately got flees, and I had to spend extra money on grooming and a messy, stinky topical flea treatment (Frontline). (Don’t worry I got consulted with my vet). The Spinosad makes Trifexis worth it, though it is still outrageously expensive. I hope there is a generic soon.

  9. I am so sorry for your loss, Sarah! Please advise which medication did you use? I’ve been using Sentinel on both of my dogs for a few years now, I was just about to try Trifexis when I saw this post.

  10. Is there a generic Trifexis? I spent about $20 per trifexis pill with our mobile vet. Or does anyone know where I can find it cheaper.

  11. I have a MDR1 Australian shepherd who had a toxic reaction to Trifexis (seizures); we changed to Sentinel and he was fine. The next year (2016) he went blind after the second dosage. My heart is broke. So much for being a good mom.

  12. I put my dog on Sentinel 4years ago and she got fleas . So I switched her to Trifexis. No fleas since. While she hasn’t seemed to have any problems on Trifexis, all these stories I read and hear about scare me. If you do go with Trifexis make sure to talk to your vet first. But honestly if Sentinel has worked for you for 6 years why not just stick with that one?

  13. So very sorry for all whose kids had a reaction, and thank you for posting. My poor boxer terrier girl who has manageable food allergies and ivermectin toxicity was taken off Sentinel which had been an effective and event free treatment for a year by her new vet. New vet was informed repeatedly about that.
    She got hives , swollen feet and muzzle, a few days after her first dose. She started out going off her food, then her skin erupted and she was itching terribly, couldn’t even sleep. Seems to be easing now beginning week 3. Will have to change vets again if we can’t get Sentinel. There is a reason it can be given to 4 week old puppies.

  14. I found this site totally out of frustration. My small dog falls for anything disguised as a “Snack”, so she’s easy to medicate. However I have a 75 lb Lab also …., He does not think their a “Delicious flavored Chew”, in fact he gives me the, you eat that thing look. If I smash it up and put in his meal or snack, he won’t eat it. Trust me this beast doesn’t pass on food. It’s Ginormous, in order to accommodate his weight. Forcing a pill that size on him Is like wrestling a Bear !! No cheese won’t trick him either. I spent a pile of $$ on them, and they are super effective. I’m just wanting to not give him to the Circus every month. GEEEEZZZ !!!

  15. My pit bulls were on Sentinel last year (they were 1.5 years old at the time), and they did great. No reactions, no buggies, no problems.

    After reading about other dogs’ side effects and long term health problems, I became weary of conventional preventatives. I did some research and saw that a lot of people swore by natural remedies. Of course it sounded promising and the overall the best option being it was natural, had no side effects, no long term health problems, and being more cost efficient. (Apple cider vinegar, brewer’s yeast, diatomaceous earth, probiotics, etc)

    Of course, there’s that age old saying “if it sounds too good to be true, then it probably is.

    I was consistent, patient, and relentlessly hopeful. But after 3 months, my dogs had fleas (never had fleas on Sentinel) and intestinal worms (never had worms on Sentinel). Granted, they spent a lot of time around our roommates untreated cat. She went in/out of the house very often. This may or may not have been a contributing factor to the natural remedies not working. I like to believe it was, because natural medicine has always yielded great results for my human ailments.

    Anyway, I put them back on Sentinel while continuing their natural remedies. Our roommate recently got a dog who is not on preventatives. Our dogs, however, do not seem to be affected as of currently (it has been 1 month). This leads me to believe in the efficacy of Sentinel (plus the powers of natural medicine).

  16. I just sitting dog for friends , dog sleep 24 7 constantly , lethargic , I never ever see horrible drug out dog , poor dog id on Sentinel and Corthofen.
    He is drug out completely . Please people stop drug out your DOG’S. I am devastated, USE NATURAL STUFF, LOOK ON INTERNET . DOG’S SUFFERING TERRIBLE FROM HORRIBLE INTERNALS SIDE EFFECTS

  17. This is for Amy H or anyone having a problem getting their dog to take trifexis. I have learned if you go to your local health food store you can buy large size gel capsules. I crush the trifexis and fill them,yes it does take a few of them and I really have to pack both sides. My boxer Brady gets boiled boneless skinless chicken breast in his food so I take some of it and blend it into chicken paste and coat them!!! My vet said that is fine to do and it works.He has had two cancer surgerys and this is the only way we can get him to take any pain meds ect. I also will put the coated capsule in one hand and just a ball of chicken paste in the other, as soon as I give him the capsule I offer the ball of paste and down goes the capsule. being sneaky is the trick.

  18. Amy sorry just saw the reply button after I posted. look down for my post from Donna G. I went through the same thing till I found the trick ! Good luck

  19. I was able to administer Trifex to my dog covering it up with peanut butter.

  20. Crush up the pill (not too crushed) and mix it in some soft food (I use the Beneful prepared meals in the plastic containers/or if you make them something special 😉 Give it to your dog right after though as to not let the meds sit and dissolve. (as told, and read) With these meds it is advised to give with food any way. Helps to prevent nausea/vommiting etc. 🙂

  21. I am so sorry for any loss of pet due to any reason beyond our control. I have worked as a vet tech in Hawaii and the most difficult situation to deal with is a pet loss due to heartworm. Over the years I have used Trifexis and have been very happy with the results on all of our dogs: Boxers, Border- Kelpie, Boxer-Lab and Bull Terrier. Recently our vet switched us to to Sentinel to offer a cost savings…Not happy that my dog can’t sleep with me because he now has adult fleas. Not happy. Am switching back to Trifexis tomorrow.

  22. I gave my healthy 2-year-old golden Trifexus and he had a terrible adverse reaction. We gave it to him after dinner, about 7:30PM, and at 12:30PM he woke up and was acting extremely strange. He wouldn’t sit down, was in a weird trance state, kept opening his mouth in a yawning motion (but wasn’t yawning), would sit with his nose pointing directly up to the ceiling, and was extremely antsy and anxious. We sat up for 4 hours watching him and deciding whether or not we should take him to the emergency vet. He fell asleep about 4AM and seemed a bit better. I’ve had a golden with seizures before, and this was not that. I googled “adverse reaction to Trifexus” and all the videos were almost exactly how my dog was acting. We made an appointment with our vet the next morning, and they ran blood panels and other tests which all came back normal. Although they told us that it does seem like this was a reaction to the Trifexus, they could not confirm. The ONLY thing that this could have been from was the Trifexus. I noticed that our vet gave him the 60lb-120lb dose, and he’s a pretty small golden-probably 60lbs wet. I don’t know if this could have had something to do with it. I will absolutely not be giving him this fea medication EVER again, and am researching additional medication: we’ve been advised to try sentinal and revolution (topical). I’ve extremely scared of giving him another oral medication, however.
    Beware when giving this to your dog- and research, research, research!

  23. We used trifexis on our chocolate lab twice and she was sick for 4 days with the diarrhea each time. Never again this stuff is toxic to pets…

  24. Gave what? Sentinel? or Trifexis?

  25. I have Australian Shepherds and was told a long time ago never to use products with Ivermectin as an ingredient. My girlfriend used Heartguard for her Aussies and two started having convulsions…they both died eventually and a Vet told her he felt it was a build up of the ingredient Ivermectin. I try hard to buy Interceptor but can’t hardly find it any longer so it looks like my only option with be Sentinel. I also use Comfortis as my one Aussie is so allergic to fleas but now can not get it in Australia…we are in the good ‘ol USA where you no longer can afford to have pets.

  26. We’ve been using Trifexis for years with our Chocolate labs. No issues, but the large pills (for 75lb dogs) are apparently really bad tasting /smelling. Neither of our dogs will willingly take them and find them in everything!

  27. I have a Chihuahua and pit bull mix. he is maybe 2lb!!! my doctor told me to give a half a dose now and next month the other ? is what do other think and should I go ahead and give the half..
    Im just nerves to give it to him do to he is so small and young!! how ever I need to treat the stool worms!! please let me know your thoughts asap.. Im so turn on what to do!!

  28. I just experienced adverse reactions using Trifexis on my 4.3 pound yorkie. He became very lethargic and vomited twice and the poor thing had muscle twitches. It lasted a full 24 hours. Even his eyes were half masked and it seemed he could not focus. He is 1 yrs. old. I will NEVER use Trifexis again.

  29. My dog hates taking his trifexis, I tried to look into an alternative but doesn’t seem to be another one out there. He is a 2 year old terrier mix, 11lbs.

  30. I lso, cannot get my 8 yr. old Bichon to take it. I’ve tried, cheese, peanut butter, ice cream, but she can smell it no matter what. Actually, I can’t blame her, Trifexis smells so bad, I can hardly crush it up with out turning my head for a breath of fresh air. And, the pill is so large, I refuse to try to cram it down her throat. She, is 21 lbs, and on the 20.1 – 40 lb pill. Why can’t they (Elanco) at least try to coat the pill with a slick coating to help the pill go down in one gulp, and to mask the odor. These are pets, part of our family, they deserve a little consideration. They can do it for people, they SHOULD do it for our girls and boys. People understand when they are given a medication that is gross to help them stay well. Our kids just know that mom or dad is making them take something that they hate.
    $25.00 + for each tablet, they should be able (with out more R & D) to make a tablet ALL dogs can get down. But, then your kid may just keep it down each time. But, instead you get advice….if your dog throws it up, then give him or her a second tablet. Unless, I’m not able to add, now we are at $50.00 a dose.
    Seems to me, cool old money may be at the center of our problem. We keep buying, they don’t change a thing, our little ones are the ones that pay the real price. Elanco doesn’t care, why should they…they aren’t the ones who force this medication down our kids throats. If this was a human child we would not put up with this situation, when there is a simple change they could make.
    Yes, I keep on doing it to protect my little girl. But, it’s getting harder and harder to keep forcing my girl to take this. My little girl looks up at me every time now, wondering why I am doing this to her. And, I’m getting sick of it.

  31. Moved to SC in summer 2015 and our vet switched both miniature schnauzers to Trifexis from Sentinel. Said the worms, fleas, etc. were terrible here. Two months later one dog would have diarrhea within several days of taking Trifexis. The other one was fine. It took us a few months to figure out the cause and we stopped it, but not before the sick one developed irritable bowel syndrome. That was followed in 8 months with adenocarcinoma, which took him relatively quickly. I’m convinced that Trifexis started him down this path (his first 6.5 years were great) as he mirrored the 1% of dogs with severe reactions on the Trifexis warning sheet. I’ll never use Trifexis again! Have been on Revolution since then with our other dog and recently got a new puppy. Thinking about going back on Sentinel since they never had any problems and it’s a stronger preventative.

  32. We’ve been using Trifexis for several years on our our 100% Custom Blend Terrier who usually weighs around 52lbs, and You’re right about the smell. We have a custom blend 100% terrier who typically weighs 52 lbs~. It is a battle each month, we’ve tried all the tricks we can think of, though we are limited on what tricks we CAN use because she is prone to pancreatitis. Some months we wind up just having to shove it down her throat which afterwards inevitably makes me feel guilty. I so wish the manufacturers would do something to coat these nasty smelling pills and make them more palatable. In truth, however, what disturbs me more than anything is the fact that I am basically giving my pet what amounts to an oral pesticide. All the pesticides I know of are poisonous. Why give one to my dog? Couldn’t this potentially cause problems somewhere down the line, or in some cases immediately? Why can we not develop something less harsh, more “organic” if you will, more natural but still effective. I can guarantee the solution is out there, we’re just not looking in the right place, or looking for it at all!

  33. I would really love to give my dog something other than Trifexis, but Sentinel not killing adult fleas bothers me. I’m still doing research but it seems many people use a combination of both oral and topical meds? I just have to find the best combo for my dog because she HATES Trifexis and it’s a struggle administering it monthly.

  34. I have had apprehension about using Trifexis for my Shih-Tzu, however he has been on it for over 2 years with no apparent issues. He will NOT eat them no mater how I try, I’ve used Pill Treats and they make him throw up every time, if I break it up into his food he will pick out the pieces no mater how small I make them, or not eat it at all. I am now just putting them down his throat, which he doesn’t seem to fuss over.

    I have not tried Sentinel as it does not kill fleas which are rampant in my area, and I really don’t want to have to give him even more medications. I do use topical flea treatments after every bath, and if I see any (living) fleas on him.

    I had tried HeartGuard but haven’t heard great things about it, and it is very limited to only heartworm protection.

    It is a shame that they charge so much for Trifexis, and Elanco is a crook and on on several occasions wouldn’t honor the rebates I’ve sent in. So buyer beware…

  35. I agree with Char and Rob, regarding the horrid smell/taste of Trifexis. I have 4 dogs between 4 lbs and 9 lbs, ages between 5 and 7 yrs. The two smallest (4 and <5 lbs) get 1/2 dose monthly. I have been putting it in soft cheese and/or peanut butter and giving it before breakfast when they are the most hungry. Annie, my 5-lb toy poodle, can smell heavily disguised Trifexis before she even gets close to it and turns to run away. I've tried giving her 1/4 dose (twice) and sometimes can get her to take one of those. I have even taken her to the vet to have two techs try to get a half-dose into her in pill pockets and finally using a straw-like gadget that you blow into to get the pill down. That took half an hour. I have written to Elanco about their stinky product a couple of times and received no reply. I'm going to ask my vet about using Sentinel instead of Trifexis, at least for little Annie.

  36. I’ve been giving my dog Trifexis for years. I’ve never had a single issue with negative side effects, etc and the medications have prevented all that they have claimed to. Previously, he had been on Heartgard. I switched him over for the added coverages. I’m truly very sorry for the loss of your dog- but as stated by a previous commenter, you really shouldn’t make such claims and not specify the medication given. As you can see, it causes a great deal of concern and confusion amongst other posters and can hurt a business unfairly.

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