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

Get Sentinel at 1-800-PetMeds.comGet Trifexis at

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 4.6-star rating average from 341 of our online shoppers, and Trifexis has a 3.8-star rating average from 68 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.


  1. Kat says

    I’ve got a 4 month old miniature Australian shepherd and I’m trying to decide which medication to put her on. Her breeder specifically said never to give Aussies ivermectin as it can cause seizures and even death… Unfortunately, one of the pups in the litter was exposed to it and eventually passed away. I’m scared to give her anything based on all the horror stories here. After noticing a bunch of pimple like bites on her I finally washed her in a sentinel shampoo and applied sentry fiproguard. Any recommendations as to what I should do next? A vet recommended trifexis but I’m just not sure. I live in South Carolina and fleas are definitely an issue.

  2. Mary says

    I started giving my two corgis Triflexis in May, noticed my tri color was very lethargic after first time. Ask the vets office, she said divide and give two days in a row in food. Tri color still lethargic, so this month we are switching them to Sentinel. I have never had flea problem, so mainly concerned with the heartworm disease, which our vet said she is seeing a lot of now. Anxious to see how they do on Sentinel. Have not had them on heart worm medicine until this year.

  3. Courtney says

    My puppy was on Trifexis for 4 Months before we figured out the adverse reaction she had to it. Everytime after we gave her the pill she just couldn’t hold her bladder and even odder was that she wouldn’t jump into the car or anything.

    Every month we gave it to her she would have bad diarrhea and would pee in the house. It was terrible because we would be going to take her out and she would pee while going outside. She just couldn’t hold it. She also seemed to get “infections” for a week every time after we gave it to her.

    A month later after being off of it we haven’t had any issues and she jumps into the car without a second thought. Which is nice because I was tired of lifting her into the car. I just really don’t recommend Trifexis. Is you notice anything different after giving it to them you should be really careful, because their body is telling you they can’t handle it; especially if they are vomiting on it.

  4. Mary says

    I have given both my black toy poodles Triflexis for 2 yrs. I have had throw-up with meals or several hrs later. I now give it 3 hrs after a meal. At least if they throw-up then, I feel sure the pill has dissolved. A few months ago my black male has developed light patches. He is not of ‘parti’ bloodlines. He is also showing lots of wht. hairs and appears to be a charcoal color now, not solid black like his sister, who has had no hair color change. My question is, can Triflexis cause this change of hair color?

  5. Abby Rosenberg says

    Mary, according to the manufacturer the following are potential side effects:

    “Like all medications, sometimes side effects may occur. In some cases, dogs vomited after receiving Trifexis. If vomiting occurs within an hour of administration, redose with another full dose. During field studies, no severe or prolonged vomiting occurred. Additional adverse reactions observed in the clinical studies were itching, decreased activity, diarrhea, inflammation of the skin, redness of the skin, decreased appetite and redness of the ear. All reactions were regarded as mild. For technical assistance or to report a suspected adverse drug reaction, contact Elanco Animal Health at 1-888-545-5973. ”

    ~ Abby, PetMeds Pro

  6. jacki says

    I have had my current Rotties on trifexis since they were young and my Rotties prior since Trifexis first came out. I love it.. No fleas. which is hard to say when living in Florida. jIust put a little cheese on it and they swallow it down. I agree with others that as with all meds, each person/dog is different. I love trifexis and will continue using it.

  7. Nick says

    Fact of the matter is, dogs are like people, every dog will react differently to the medication. Some dogs may have minor side effects, some may have severe and some none at all. I give trifexis to my 2 year old beagle and she is fine every time. No vomiting, no loss of energy, loss of appetite etc. so everyone who is worried about giving they’re dog one or the other of these two meds, you’ll either have to just try it on your dog or go without. The only way to know is to try and remember some dogs are more sensitive to medications than others. But in my case I love trifexis for my dog, it works great. She has even been around and played with another dog who had fleas and never even scratched herself once or got any parasites. I give it 5 out of 5.

  8. says

    I have been researching trifexis because my Rosie (mix) has started having trouble not being able to hold her bladder. Never had this problem until we gave her trifexis. She also vomited a couple hours after her dose. She laid around fro 2 or 3 days and I thought she might be pouting because of her vet visit. She had to be trimmed and anytime she has to leave the house it seems to traumatize her. But now after reading these posts I think it was the medicine. She will not get another dose of Trifexis!

  9. James says

    I have used trifexis for 2 years and it works great on my goldens. It is the first medicine I have ever used that has prevented them from getting any fleas. It’s the best.

  10. Jaclyn says

    Anyone ever have limping problems as a side effect of Trifexis? Our rottweiler/pit mix has been on Trifexis since she was 4 months (she will be 2 in november). The only side effect she’s ever had is a little more tired than normal. Well last night we got home from our neighbors (we were gone not even an hour) and she greets us at the door with her back right leg hoisted in the air. She wouldn’t put it down or put any pressure on it for 20 or so minutes. The only thing out of the ordinary that she did today was take her Trifexis for dinner. NO idea if this has anything to do with limping. I have been up every hour tonight checking on her laying in her bed next to my husband. She seems fine now. I used to swear by Trifexis but if this horrible, painful limping is a side effect of it I don’t want anything to do with it anymore!

  11. Lauren says

    I had my puppy 16 week shep mix on sentinel and it did nothing for her! Sentinel does NOT kill adult fleas! Nor is it a preventative for adult fleas. My vet recommended Trifexis and so far it has worked great! It was a little bit of a struggle to get her to swallow it (just put it in peanut butter) Obviously no medicine is going to taste great. My entire family has all their dogs on trifexis now :)

  12. says

    I am looking at switching to one of these products. I have a 7 yr old Min Pin who has been having flea issues lately. I dip, spray and bath only to have fleas again in a few days. We have been having an extremely wet summer and I think the conditions are perfect for flea breeding. Any input would be helpful as I wish to make an informed decision and do not want to jeopardize my dogs health.

  13. Jackie says

    I have an English Mastiff and a miniature schnauzer and they are both of Trifexis and I have NEVER had an issue. I entertained the idea of looking for something a bit cheaper but money really shouldnt be an object when caring for my babies so I am sticking with it. I have been using Trifexis about since it came out and its amazing and no problems nor have I ever heard of any problems with it so I will stick with it.

  14. Maritza says

    I just purchased Sentinel for my dogs – switch from topical for fleas & ticks & Heartgard. What has been the overall experience in reference to switching? I’m truly concerned about any flea problems as I haven’t had any with the change.

  15. DJ, Soco and Bentley's Dad says

    We have had our babies on trifexis since birth.. Soco has been on it for 4 years and Mr. Bentley has been on it about 6 months now.. They have had no problems except neither like the taste.. I break them in to about 5-6 pieces and feed it to them in some cheese and they’ll eat it right up.. No vomiting and they seem to feel totally fine/normal after dosing.. I came online to search to see if PetSmart had it and came across some pretty scary S&#$ about it, but that’s usually easy on the internet.. It’s only good to scare you.. I think you can find something saying it’ll kill you regarding just about everything on the internet.. I took a new med once and went into anaphylaxic shock and couldn’t breathe and had crazy muscle spasms, so that kind of thing can happen to ANYONE.. But I called 911 and got fixed up and was fine.. Just ALWAYS keep a constant eye on your pet for the first few DAYS (Yes, DAYS) after giving your beloved pet new meds because they can’t always come tell you they need “911”

  16. MomaJo says

    The Trifexis pills have a very unpleasant smell and I assume taste. My 98lb Lab, Wilson, would spit the pill out of anything I tried to hide it in. Several months ago I had an idea to try and cover up the smell of the pill so I crushed it up in a can of sardines. Wilson ate it all up with no issues. He has had no adverse issues taking Trifexis.

  17. GoldenMom says

    I used Sentinel for 2 dogs successfully for many years. Treated them with Capstar after boarding just in case. When Sentinel became unavailable, we switched to Trifexis. Suddenly my Golden began having ear infections. Now she has horrbile skin issues (the other had passed after 14 years). We’re going back to Sentinel, now that it’s back. Hopefully, the anti-fungals, probiotics and vitamins will get our beautiful, wonderful, fur baby back to full health. I swear by Sentinel – never saw a single flea in all those years we used it, and it was safe for my now-deceased herding dog who could have had issues with other products.

    P.S. – My dog also spit out the Trifexis repeatedly. Maybe these pups know something we don’t.

  18. says

    I am a breaded of the most awesome dog in the world, the Australian Shepherd.
    My Aussies have all been on Sentinel since they were 4 weeks old. In 12 years, I have never SEEN A FLEA, never had to have one treated for worms, never had a dog require treatment of Heart Worms.
    I keep a supply of it on hand and you couldn’t pay me to switch to trifexin or anything else. It ain’t broke, so why should I fix it?

  19. kerry says

    Recently after taking trifexis for a year our Snoozy (terrier mix) became ill 7 days after pill started licking carpet etc eating some grass-symptoms abated then within more days became worse. brought her to vet who gave her valium to no avail-vet thought she was stressed. ? no stress that i know of) that night up all night while she incessantly licked carpet everything and all she would do outside was eat grass-back to vet after she started vomiting. Brought her back to vet who did a barium sturdy with ex-rays no obstruction gave her cerenia by injection. Brought her to emergency medical hospital after she developed bloody stools from diarrhea and she became lethargic. After 24 hrs IV fluids, antibiotic, antifungal med she improved. Brought her home and saw the info about trifexis on t.v. I will call vet today and request another med.

  20. Mike says

    My shih-tzu and Maltese-shih-tzu both have taken a year of trifexis with no problems whatsoever. They don’t consider it a treat, though, and take it with peanut butter or cheese.

  21. Gary Eaker says

    I have a 4.5 year old AmStaff that came to my family 6mnths ago in FL from SC. Tank was 70lbs of pure muscle that loved to run and leap like a deer. When started on Trifexis 6 mnths ago he seemed to tolerate it just fine. After 4 mnths of Trifexis he tore his cranial cruciate ligament in his right leg. Then 2 weeks later he did the same to his left rear leg. I don’t know if Trifexis had anything to do with this or not but the scary stories about dogs suffering and dying are terrible. Wouldn’t it make sense to make a first dose of Trifexis about a tenth of the normal dose as a tolerance test? Then if a dog has any adverse reactions perhaps they won’t get seriously sick or die?

  22. says

    We have been battling our adult Pug’s skin problems for 18 months now. She itches constantly and crawls on her belly to itch to point of bleeding. Terribly frustrating. We have eliminated everything from her diet except Superior limited ingredient dog food, and only treats of cooked turkey. After a round of steroids and a vow of NO extra food sources she was doing really well until suddenly, itching and scratching again. Another round of steroids, doing well, then AGAIN suddenly, itching and scratching. Today it dawned on me……she was flaring up each time I gave her the Trifexis that we put her on 18 months ago. Damn I wish this stuff would have a disclaimer on it to watch out for skin problems. Will definitely avoid this stuff in the future.

  23. says

    Trifexis Users Take Note: We have a hound/lab that was a rescue dog. We got him when he was a year and half old. Very healthy dog. He just turned five years old. All shots, regular check-ups with absolutely no issues. Switched him to Trifexis when Sentinel went off the market. He has been on Trifexis for over a year. I never associated any side effects to the medication but he was known to have spells of eating grass, being a little lethargic at times but he always perked up after a few days. Again, I never was looking to find that his monthly medication (Trifexis) was a problem. I do know that he did not like taking it and I told the vet recently that he does not like taking it even though he loves any kind of treat. So, he has been on Trifexis for over a year. On January 17, I give him his monthly dosage. My husband notices that his head is really warm and that he must be running a fever. I made a mental note that he had just taken Trifexis two days earlier. He seemed lethargic and I commented to my daughter I thought Buddy had cabin fever. We all tend to get this in the winter. Another week or so goes by and on Sunday, Feb 2nd, he was laying in his bed and all of sudden started jumping up trying to get his feet under him and he could not stand. His legs were out to the sides. He had no muscle control, he was drooling profusely and shaking. His eyes were rolling round in his head and he had the look of terror on his face. I got him over to the tile floor because he was drooling so bad and thought the cooler floor would be good for him. I got the hospital on the phone and talked to them. They said it sounded like he broke a fever and had a seizure. Being familiar with children/adult seizures, it was exactly what I said that it was like he had a seizure. Within a few minutes he was recovering. His heart was beating more normally and he was able to stand up after about 10 minutes. What a scare! I took him to the vet the next day. I asked her if it could be the heartworm medication because of the things I identified above (fever, lethargic, etc) She said there is no medical evidence that Trifexis causes seizures and that bigger dogs especially retrievers are more susceptable to seizures but not associated with the drug. Though she did not think it was Trifexis she said we could switch him back to Sentinel. I said that we would do that and I would bring the remaining pills back for refund. She agreed. Later that day, I got on the internet and found all these people who had lost their dogs possibly due to Trifexis. Though I called the vet and told her, she still held her ground that there was no medical evidence. I re-minded her to keep checking those medical journals for their findings but in the meantime my dog was not going to be taking Trifexis for sure. Buddy’s seizure was 16 days after he took the pill and this is very consistent with what some of the people say that it is about 2 – 3 weeks after the med is taken. So, all of you that have been using this med without any problem…be ware. It may build up in their system or react after a delayed period of time as far as I am concerned. I also think I ignored some signs along the way that I should have documented. He is a very healthy dog and I hope that he does not have another seizure as it was an awful experience for all of us.

  24. Matt says

    Just used Trifexsis to treat my 200 gallon reef tank today. Used the whole pill against acropora eating red bugs. Seemes to have worked at killing the bugs. After 12 hours I returned my carbon to the reactor and turned my skimmer back on. The overall result. Dont see red bugs. Some corals are not very happy, others seem OK. Off to do a water change today. My protein skimmer is pulling a lot out of the water.

  25. Alex says

    I wanted to comment that my dog has been pretty much fine so far on this med. I wonder if these 700 people know that Heartguard has killed more herding breeds than trifexis has killed any dogs. 700 cases since it was introduced, I’ve read more and seen more scientific papers on how many dogs have seizures and die from heartguard and Iverheart.

    I may be wrong about trifexis and my dog may one day have a reaction but so far its the lesser of two evils.

  26. Wayne says

    Our Australian Cattle Dog, currently nine months old, has been on Trifexis since she was 12 weeks old. She has never vomited after taking it, she is never lethargic, and actually takes hers like its a treat. We have had no problems with here loosing hair, itching or any other side effect as far as we can tell. As with any medication, I am actually more worried about long term effects, but it is only a concern and I haven’t seen anything saying that there could be long term effect. We also use Trifexis on our 12 year old rat terrier and my in laws use it on their dachshund terrier mix, none of the dogs have experience any side effect, but they do not like taking it. We are very happy with this product.

  27. Mark says

    I have a 3 year old, female, German Shepherd / Retriever Mix who has been on Trifexis for almost a year without any problems; and she hasn’t had any Flea or Worm issues, either. I would recommend Trifexis, but like all medicines, especially the ones that kill a parasite, I would discuss it with your Vet and monitor your Pet. If your Pet has issues with other medications or foods, then I would consider all of your options. Personally, I think Trifexis is a great product.

  28. Bobby says

    Trifexis works. I’ve been using it almost a year. I’ve never tried the cheaper Sentinel. I want to try it because it’s cheaper, but it says that it doesn’t kill adult fleas. I don’t see the point in using it. I have two dogs on Trifexis. One one year old female Rat Terrier and one three year old male Chi/Dach. I love my dogs. I hate fleas.

  29. Kim says

    I have a two year old golden retriever who has had bladder control problems but after being tested twice by my vet and being on antibiotics twice we thought she was fine. She would urinate in her sleep and only in the evenings. My vet put her on Proin which is supposed to strengthen her bladder sphincter. She was doing great with no accidents for 3 weeks. I gave her trifexis yesterday and this evening at 7:30 she was asleep and had an accident. I’m sorry but she is completely house broken, was fine for three weeks, had trifexis yesterday and now an accident. Seems pretty funny to me plus she gets very lethargic the day after she gets it.
    If you read the directions with trifexis, it does NOT kill or repeal ticks. It’s time to look elsewhere for flea/tick/worm meds. My dog will not be taking any more trifexis.

  30. Ashley says

    I switched my 2 dogs, a 3 yo Shar Pei/Rottie and a 1 yo Rat Terrier, to Sentinel two months ago and it sucks! They’ve always been on Trifexis and have never had any problems. No vomiting, never lethargic and never any fleas!! We tried the Sentinel out because it is cheaper but now my 3 yo has terrible flea dermatitis so we will be going back to Trifexis next month. I believe dogs react differently to medications just like us humans. I’m sorry to everybody who has lost their dog after taking ANY medication :(

  31. brigitte says

    To the person asking about revolution. I had all my dogs on Revolution and never had any problem with heartworm or fleas or anything else, but you have to be consistant and make sure until it dries they don’t rub it off.

  32. frank says

    I treated my 2 Golden Retrievers with Sentinel for years without any problems. The flea control was excellent and I liked knowing we were preventing worm & parasite infections. These dogs both have passed on now. I never realized there were so many adverse reactions associated with this drug. I am currently shopping around for the least invasive, safest flea treatment for my new dog, an Akbash rescue who has a reported flea allergy.
    My neighbors treated their beautiful Goldendoodle with Trifexis for over a year before they realized it was causing major health problems. He was sick, lethargic, lost all his hair, and had terrible skin reactions. Their Vet did not associate his illness with the flea medication until after they had spent thousands of dollars on unnecessary medications and testing. He was fine after they discontinued the Trifexis.
    After reading all of these horror stories I am hesitant to use any oral or topical flea pesticides on my pets, but if I really need to treat them, I would start with one dose and monitor them carefully for side effects.

  33. Kristopher says

    Speaking from experience, I’ve had 1 Corgi Mix on Trifexis for some time now and had 2 poms on it for quite a while too.. none have showed any adverse reactions to it at all.. now i won’t say that some dogs don’t have adverse reactions to it but, I won’t believe some hype that people are trying to spout without proper research being done.. for all that is known, they could’ve had some sort of other problems or even infested with heartworms when they took their first dose.. supposedly (i’ve heard) if they have heartworms ahead of time, then it could cause problems.. which is why any responsible vet will run tests on your pets before assigning medicine all willy-nilly.. heck we had to have multiple tests run for heartworms before our vet would even give it to our dog.. but as others said, just like people, animals can have adverse reactions that won’t be present in every dog..

  34. martha says

    my yorkie throws up every month (after about 8 hours yellow bial) and gets lethargic …but my vet says he has to take it… and my chi.pom runs when he hears me opening the trifectis and sleeps all day after dosage (unusual for him)… and my chi.minpin gobbles it up without any force but throws up sometimes.
    …something inside me tells me this can’t be good…. but my vet insists it’s safe.

    i wish there is another solution.

    i will try cutting these in half and giving 1/2 morning 1/2 evening with food and pray they dont throw up twice…

  35. Blake says

    The best way to get them to keep it down is to feed them some fatty foods (canned food, roast chicken skin, hot dog, etc) with the meal, then give them the trifexis AFTER their meal. Works every time. Do not give BEFORE the meal or on an empty stomach.

  36. Blake says

    ANd if treating multiple dogs with the possiblity of vomit, put them on a different schedule so you always know who threw up. (ONe on the first of the month, the other on the 15th…)

  37. JT says

    My 9 lb Havanese used Trifexis successfully for 2 years, no fleas or parasites, but then the vet stopped carrying it so she was switched to Sentinel. It’s been a total disaster. My 2.5 yr old dog now has flea dirt really bad on her back, scratches all the time, and is eating grass and limping. I’m going to insist that she be put back on Trifexis this week; enough is enough. I think that using a product (Sentinel) that doesn’t kill adult fleas is useless and causes too many issues.

  38. Lisa says

    My dog started trifexis and refused to eat it. He eats EVERYTHING! That should have been my clue. He was taking this for about 6 months when all of a sudden he got spooked and started trembling. I had never seen this before and thought he was dying. Scariest thing in my life. I called the emergency vet and also called my regular vet. They couldn’t find anything wrong with my 9 yo yellow lab. Well then about 9 months later he did it again, and a week later again. Trembling and looked frightened, couldn’t stand or walk…basically paralyzed. I called the vet and described this. They said no probably not a seizure since he didn’t lose consciousness or bowels. They recommended an MRI and CAT Scan. Very expensive. I videoed the next seizure a week later and took it in to the vet. She called it a focal seizure and said take him OFF Trifexis immediately. I have and no problems since. Just got sentinel and am terrified to give him as i don’t want to experience what I went through last year.

  39. Julie Anne Garlit says

    I had three perfectly healthy Goldens with wellness panels to prove it. Only change was Trifexis. After 2 doses my first Golden died from hemolytic anemia. One cause is poisoning. My second and third dogs both had extended periods of vomiting and diarrhea with vet bills to match. Had three case numbers from Elanco. Of course, they denied any responsibility. My second Golden just passed away suddenly and unexpectedly. Refused to eat in the morning. Lethargic and disinterested in daily activities. We never made it to our vet appointment. He passed away into arms. My third Gokden has had serious GI issues since Trifexis. Do not risk your pet’s life or health with this drug. I wish someone had warned me. It is hard enough to lose a pet but this makes no sense. The FDA is supposed to protect us from things like this. Elanco should not be in the animal welfare industry. Now they have purchased the company that makes Sentinel. Buyer beware!

  40. Linda says

    My basset was in good health til trifexis. All I can say is if your dog spits it out and doesn’t want to take it or has side effects,….the dog is trying to tell you something.

  41. Cathy says

    All of these products will kill your dogs. They are dangerous pesticides that are designed to destroy the central nervous system of the heartworm parasite, and will do the same to your dog. My dog died from a single, partial (he threw up most of it) dose of Trifexis, and Sentinel has the same ingredient as Trifexis. Educate yourselves on just how infrequently heartworm issues really occur and how long it would take to impact your dog if your dog actually got a heartworm parasite, and you’ll stop giving these poisons altogether. Get Dr. Will Falconer’s ebook on the subject, and raise vital animals that won’t get heartworm disease.


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