ProHeart-6 Returns, with caveats

Proheart(2) You may recall that I posted previously on my concerns about our heartworm preventive medicines becoming less than 100% effective.  There seems to be no difference in efficacy between the different medications, nor does it appear to be dose-related (i.e. giving a 100-pound dose to a 51 pound dog doesn't guarantee effectiveness).  I even tried dosing my own dog twice monthly, using different preventive medicines (she got heartworms anyway — not bad, but she has them).

So what if they were taking preventive medicine constantly?  That's what we used to do with daily preventive medicine, but we had trouble getting all the dogs medicated every day, year round.  We had compliance problems from both the dog and the owner. 

We also used to have continuous daily heartworm preventive medication that was pretty much trouble-free.  ProHeart-6 was given by injection once every six months.  It was a timed-release medication — basically, you injected a blob of medicine under the skin and it slowly leached into the bloodstream for the next six months.  I didn't have a lot of clients on the product, as it didn't control the intestinal worms like Heartgard-30 or Interceptor, and it didn't control fleas like Revolution.  Also, we had occasional problems with people coming in a month or two late for the next injection (not good).  We had no medical problems with the product, though.

That's why I was flabbergasted when (with no warning from the manufacturer, Fort Dodge Animal Health) the product was pulled from the market.  It was all over CNN after I went to bed, and I didn't look at Veterinary Information Network until after clients began calling on the Saturday morning in September 2004.  The FDA mandated its removal, citing many adverse reactions, including patient death (which I admit is a bad thing).

The funny thing (funny-strange, not funny-haha) was that the product continued to be used in other countries around the world with no apparent problems.  No explanation there, just the FDA "looking out for us" ( I guess Fort Dodge didn't slip them as much cash as Eli Lilly, whose psychotropic drugs list everything they are prescribed for as potential side effects, including suicide.  I don't feel like the FDA is looking out for us so well, there.).

Well, ProHeart-6 is coming back, but I can't buy it until I complete my one-hour web seminar this week.  It will only be available through a "restricted distribution program", whatever that means.  Not only will we not be using it in sick or debilitated animals, we also won't be using it in animals that are underweight, or who have history of weight loss (this being America, there won't be many of those).  AND we can't give it within one month of vaccinations. What that says to me is that they don't want to get blamed for any vaccine reactions.  Fort Dodge doesn't want to take any lumps for somebody else's lumps.  I can certainly understand that, since it took them four years to get the stuff back on the market.  On the other hand, I know that my clients won't exactly be happy about having to schedule extra visits.

On the other hand (is that three hands?), if ProHeart-6's daily continuous release of medication makes it 100% effective in those big outside dogs, they will be picking up more market share with my big, outside dog patients.  I'd sure like to be able to give people back the confidence they used to have in their heartworm preventive.

36 thoughts on “ProHeart-6 Returns, with caveats

  1. Sheila says:

    You won’t be able to give me back any confidence in this product. When this product was originally pulled off the market, the FDA cited over 5,500 adverse reactions, over 500 deaths, “some” of those deaths linked convincingly to the medicine, according to an MSN article. In addition to death as an undesired endpoint, the non-fatal reactions of lethargy, bleeding, vomiting, heart and liver problems, and seizures are side effects I would think not desired from a quality of life point of view, especially when potentially experienced for the duration of the 6 months of the time released medication.
    I am skeptical about ProHeart 6 being the answer we are seeking for prevention of heartworms.

  2. Doc says:

    The FDA press release makes some noise about re-formulation. I’ve seen the statistics relating to the original withdrawal. In Australia they have a 12-month product with moxidectin, available for several years now. I have to wonder why the product doesn’t appear to be generating any reported problems in the other countries. It’s hard to believe they just have a higher level of acceptance on sudden death. For me, it’s a case of “the jury is still out”.

  3. YesBiscuit! says:

    Couldn’t it be that the 12 month dose of the product used in Australia is a different formula (however slight) from the 6 month product which killed the dogs in the US? And that whatever that difference is, it accounts for the different safety experiences in each country? Has the new product (which is about to be released) been tested on dogs?

  4. Doc says:

    The new product is exactly the same as that used overseas. There was some reformulation in 2002. The 12-month just has more product in the injection. Both have been tested in dogs, but check out the later post on this subject.

    Thanks for reading and writing.

  5. DogLover says:

    Pro-heart 6 was reformulated in 2002 and then we all know it was pulled off the shelves in a recall in 2004. Well, it has been relaunched and the formulation has not been changed — same product that was recalled. Also this launch is called a “Risk Minimazation Program” – basically a field trial study that Fort Dodge is doing and making the vet’s clients pay for and having the client’s pets be the guinea pigs for the study. Also, the vet has to go through a webinar, then sign a waiver, and then the client has to sign a sheet saying they have been given all the warnings — so what are these sheets? Is Fort Dodge trying to have no accountability and put the liability on the vet and client? Who knows, but makes me wonder. I would be cautious jumping on the Proheart 6 bandwagon quickly as a vet or as a pet owner. Best of luck to you all!

  6. Greg Harlan says:

    I agreed to the injection on Wednesday the 9th of August. Today is Saturday the 12th and my dog is in bad shape! He displays all the symptoms that have been reported in the past on the adverse effects of this product. Now my dog has a severe kidney infection and is not doing well at all. This product does not belong on the shelf until they know what is causing this problem. My dog is an unknowingly and poorly informed guinea pig on this product and now I could loose him. I will never believe that this product is OK and SAFE I could care less what is being done in other countries.

    Greg A Harlan, Beaufort South Carolina (912) 308-8943 I will talk to anyone about this and take action.

  7. Doc says:

    I am sorry to hear about your situation. I am assuming that your veterinarian did the pre-injection blood-work so that we know your dog did not have a pre-existing problem. Your doctor will have reported this adverse reaction to Fort Dodge.

    Even though your dog is doing poorly now, I am sure that your veterinarian is doing everything he/she can to bring you guys on through. Don’t give up hope.

    Thanks for reading and writing.

  8. Linda says:

    We lost our shih tzu to ProHeart 6 that was administered at the exact same time as his rabies vac. We were not given any info, warnings or anything that there could be any adverse reactions. He was healthy prior to these injections. I want something done to the vet that did this !

    • Doc says:

      Hello, Linda,
      That is a very unusual occurrence. We regularly give heartworm preventive at the same time as vaccinations. ProHeart 6 has been back for several years with no problems. It was never taken off the market in any other country. The same company no produces ProHeart 12, which has enough moxidectin (the active ingredient) to last for one year. We’ve seen no problems with this and use it regularly.

      I can certainly understand your upset at losing your friend, but giving those two injections at the same time is not considered dangerous at all. I don’t know what happened to cause your dog’s death, but I don’t think anyone would predict such a tragedy simply from giving the two injections.

  9. Amanda VENTURA says:

    MY GRANDMOTHERS 12 YEAR OLD SCHNAUZER IS STRUGGLING TO SURVIVE RIGHT NOW BECAUSE OF PROHEART 6. My grandmother is italian she cooks with a lot of onions and garlic and loves to treat her pouch. the dog at 12 years was already anemic i could tell by the color of his mucous membranes and the slight orange brown tint / stain to his fur around his muzzle and his paws which he has a bad allergy or habit of licking compulsively (also lends to anemia) but we use to cone to discourage this behavior and my GM has started to purchase unseasoned chicken for the dog after I educated however he had seizures day 30 after receiving the injection. my GM had brought in her dog to have it groomed only. she was advised that he was due for vaccination so she complied. they were in the car ready to leave and the bill had been paid when the tech upsold my grandmother the 6 mth heartwork prevention proheart 6. he has uncontrollable allergies, he just had his vaccinations, he is 12 years old and already anemic to anyone who knows what to look for. the tech did not give my GM any warnings nor did she have her sign anything. come to find out that 50% of the product is to have been released by day 30 coincidently the day that his health took a dive. this was 4 days ago 3 days 1 night in icu a blood transfusion totalling 3500 total so far and he has another visit today to do another red blood count to see if the steroids are working by prohibiting his own immune system from destroying his own red blood cells. If i wasn’t walking him daily my gm would have lost her dog a few days ago and would have had no clue that the injection is most likely what tipped the scale for him to be in the position he is in. Most people probably wouldn’t attribute the shot since it was give a month prior or whatever thier individual timing may be from the onset of symptoms or possibly death. the info on this page is correct however that the drug manufacturer has put the onus on the veterinarian to administer the drug responsibly and rightfully so because im sure it is a great drug for a young healthy dog who isnt fed any table scrapes or has any allergies or will never come in contact with fertiziler or weed killers or anything else of that nature like floor cleaners etc that all have the same affects when exposed and that is the premature rupturing of red blood cells causing anemia.

    • Doc says:

      Hello, Amanda,
      That is a really old post. Since then, ProHeart 6 has received unconditional approval, and now we have ProHeart 12, the same drug (moxidectin) formulated to last for 12 months.

      I was not enthusiastic about the way ProHeart 6’s reintroduction was handled, but I don’t have any problem with either product at this point.

      I sincerely doubt that this dog’s problem was related to the ProHeart 6. It has been tested at five times the recommended dose without ill effects.

    • Lindsey says:

      Hi there, curious how your grandmothers dog is doing now? I have a 4 year old perfectly healthy mini goldendoodle- she was given pro heart 6 plus rabies vac on
      June 29 –
      July 23 throwing up blood
      July 31 first ever seizure
      It’s all too coincidental! It has been a complete nightmare!

      • Doc says:

        Hello, Lindsey,
        I would be very surprised if this were related to the ProHeart. It was almost four weeks before the dog began having problems, and the blood level of the drug would have been highest when first given. Weeks later doesn’t make a lot of sense for cause and effect.

        • Lindsey says:

          Thank you for your response as I know the original post is very old. This was not the first sign of symptoms, she began not eating, not drinking, and totally lethargic immediately after the vaccine. Just the drastic effects began 3 weeks after. I am curious though, if this vaccination has tiny spheres that will release (dissolve) for 6 months how is it impossible for one to not have possible side effects for 6 months? That’s the part that doesn’t make sense. The drug is in her body until Dec 29th, correct?

    • Carolana says:

      You do know onions and garlic are allergens to dogs, I get table food (dogs love cheeseburgers) but you bring up onions and garlic…I wonder if that was his cause of allergy’s.

  10. Andrea says:

    My 12 year old Border Collie tested positive for heartworms.
    They gave him Pro Heart 6 and Prednisone and Doxycycline.
    Throws up. Lays around.
    It;s like he is dying.

    • Doc says:

      Hello, Andrea,
      It is very possible that your dog has a low tolerance for the doxycycline. Some dogs just get super nauseated, even when you give it with a meal. Ask your veterinarian about discontinuing it for a bit. Then you might try a lower dose. While 10mg/kg twice daily has been the standard recommendation, there has been some work to suggest that 5mg/kg twice daily is about as good. Some dogs just can’t take the stuff.

  11. Andrea says:

    Eight days after being given Pro Heart 6, our beloved dog is dead. We just buried him.
    I will NEVER give another dog Pro Heart.
    After he became so sick and would not eat we took him off of the Doxycycline and Prednisone.
    The Pro Heart 6 killed him.
    We are devastated.
    A 12 year old dog should not have been given this drug.
    He had a slight cough from time to time, otherwise acted like a young dog.
    Ran our entire 25 acres with us, all of the time.
    In hindsight, we should have left him alone.
    Sad to say goodbye to him today.
    Pro Heart is a deadly drug.
    Oh and we paid around $700 and have a cabinet full of drugs, and Entyce(to get him to eat), syringes and RX dog food, Cerenia(anti nausea medicine) etc etc etc
    None of this did any good at all.
    From the day he got the Pro Heart 6 NOTHING ELSE DID ANYTHING FOR HIM.
    The vet suggested Pro Heart 6 as a treatment for the heartworms. Not a preventative. He was heartworm positive.
    The vet graduated in 2021.

    • Doc says:

      Hello, Andrea,
      I can appreciate your feelings of remorse and grief at the loss of your dog. That being said, while it is possible that your dog did indeed have a bad reaction to the product, I would consider that an idiosyncratic reaction. Some people can’t take an aspirin, but we don’t take aspirin off the market.

      Since ProHeart 6 returned to market, they have now brought out ProHeart 12. Same active ingredient, bigger dose in the timed release formula. No problems.

      I am sorry for your loss.

      • Andrea says:

        First, I would like to thank you for your noble and compassionate efforts to spend your time answering the concerns of strangers like me.

        Now, I have one more question. Or course, it’s too late to help our poor pup, but it may not be too late for others.
        We often hear the warning on TV adds, “don’t take this medication if you’re allergic to it.” That always seemed illogical to me because the only way to know if you’re allergic to the medication is to take it–then it’s too late. Same with our dog and Proheart.
        When administering the product as a treatment rather than a preventative on an older dog with unknown but probable comorbidities, and if such a catastrophic idiosyncratic reaction is known to be a potential, would it be possible to administer a small fractional dose to test for tolerance before slamming them with the full and irreversible six-month dose?
        Our dog displayed all the symptoms of poisoning which started almost immediately after the shot, so this is clearly not a post hoc ergo propter hoc conclusion.
        Vets may or may not know about this reaction, but they should. Our Vet didn’t seem to know about it. We asked specifically about potential complications and morbidity. Our concerns were minimized. We were told that “any treatment has its risks, but we do this all the time.”
        I’m sure that’s true, and I’m not trying to build a case or assign blame for our vet prescribing a standard treatment. But it seems reasonable to expand the base of knowledge regarding this drug to include our tragic results.
        Thanks again for your work.

        • Doc says:

          Hello, Andrea,
          I agree with your comment about wondering how you are supposed to know if you are allergic to something before you take it. I am always disturbed by the advertisements for psychotropic drugs that tell you to call your doctor if you “have suicidal thoughts or actions”. Help, I’m dead and I can’t get up.

          Moxidectin (the active ingredient) is most commonly used in Advantage Multi, where it is applied trans-dermally. When first used, you get a peak blood level in a few days, which drops off. However, with regular monthly use you tend to develop a more steady-state blood level (as opposed to the ProHeart injections, where the blood level is initially high, but then decays gradually over the ensuing months).

          I will have to ask wiser heads than mine about the feasibility of a small trial dose of moxidectin, prior to use of ProHeart product.

  12. Ashley Reid says:

    My dog just almost died from Proheart. She had a severe allergic reaction. Swollen lips and face to 3xs it’s normal size, her eyes were so swollen that it looked like she had no fur around them, she was vomiting and struggling to breathe. Since the Benadryl shot to reverse all of that she has been super lethargic and it’s been a week now and still barely wants to eat.

    • Doc says:

      Hello, Ashley,
      Has your veterinarian reported this to the manufacturer? I think it likely that there would be some support in following up your dog’s progress.

  13. Brian says:

    Our 11 year old Golden retriever with no previous health issues, given a very high quality diet her whole life got the proheart 12 shot 8 days ago. The following day she stopped eating, starting vomiting and diarrhea and became extremely lethargic, these symptoms continue today, she attempted to eat starting 2 days ago 1/4 cup boiled chicken and rice but can not keep that down, she is drinking the proper amount of water. The vomit on days 2-3 looked and smelled like diarrhea, the daily vomiting now is normal looking yellow bile with the small amounts of chicken and rice she has been eating, she has taken the 1/4 cup, 1 once per day for the last 2.5 days and throws up within a few hours. It’s a very sad fact that the fda and Pfizer executives are one on the same and zoetis is an offshoot of Pfizer with a history of approving dangerous drugs and sweeping things under the rug. My vet never gave us the info sheet letting you know you are taking a chance on your pets health, had I known what I know now (the forums are filled with dead dog stories after recieving this shot) we would have stayed with a lower dose monthly preventative. Do you have any ideas on effective treatment for my valued family member to help her digestive system to function again. She us running out of time. My local vet doesn’t seem to offer much more than iv fluids. She is drinking and I don’t want to put her through the stress of being away from us, she is very much not a fan of the vet. Based on what I have read her system will either be able to power through the poison or it won’t and she will die, do you have any other ideas? Thank you in advance.

    • Doc says:

      Hello, Brian,
      I am glad I haven’t had any direct experience this, but sad that I have nothing to offer you. One in a million doesn’t matter much if it’s YOUR one.

    • Adriana says:

      Had to euthanize my poor Leo. Got proheart Saturday and declined rapid 4 hours after the shot. Tuesday was dead. I wish I would never given him proheart. Health dog prior to that

      • Doc says:

        Hello, Adriana,
        That is incredible. I cannot imagine how badly you must feel. Were any diagnostics performed? I think the company would probably have paid for them.

  14. Alli says:

    My five year old border collie received ProHeart 12 last week. Two days later we had to have an emergency vet visit. Two days after that we had to take her back and they kept her. Bleeding from the nose, coughing up blood, vomiting, diarrhea, tachypnea, lethargy, too weak to walk. I am not at all hopeful at this point. From what I’m seeing gruff online research this is not uncommon.

    • Doc says:

      Hello, Alli,
      Severe adverse reactions can occur. I would disagree with the statement that they are “not uncommon”. I’ve used many doses with no problems whatsoever. That being said, even if it’s one in million, when it’s your “one”, you don’t care how rare it is. It can happen.

      In my area we are endemic for heartworm. I primarily use the ProHeart 12 in patients that are getting incomplete preventive medicine due to being hard to medicate, or the owner’s absentmindedness. Having to treat the dog for adult heartworms is no picnic for the dog or the owner’s pocketbook.

  15. Lesley C says:

    While I am not a vet, I run a rescue that has treated over 100 dogs that had heartworm to varying degrees. Some of the symptoms given above I have seen in patients who were not given Proheart. Extreme adverse reactions to doxycycline (very uncommon but anaphylaxic in nature), bleeding from nose and coughing (heartworm preventive given to a high positive heartworm dog without also administering prednisone). I have recently started using Proheart12 because of adopters not administering Advantage Multi correctly during doxy-moxi slow-kill protocol. Essentially, to prevent ‘user error’. No adverse reactions, though the jury is still out on whether it is as effective as Advantage Multi in clearing a dog of heartworms

  16. B says:

    Lesley this comment with some insight into seeing symptoms outside of pro heart and the nose bleeding when heart worms are present is very helpful.

    Doc, you saying “one in a million” to several people in the comments sounds a little silly.

  17. Patti says:

    We had 2 dogs that wondered up on us last summer around May. One was an emaciated yellow lab mix & a shepherd-husky mix whom looked pretty healthy. The lab was the first to go to the vet in October as he wasn’t gaining weight & had chronic diarrhea. We learned he was barely 1yr old at time( luckily he was neutered) He was started on a special diet, given vaccines & started on proheart 6 as he was heart worm neg. He has done just fine & is a much healthier happier dog. Husky mix went to vet last month for neutering & vaccines & unfortunately tested positive for heart worms. He was given proheart 6 as preventative & the vet recommended the full fast kill method for treatment. There is no way possible we could follow that treatment plan as these dogs are live outside in the country & they are very active. Oral treatment with doxy 300mg a day for 30 days was recommended as a substitute. We have not started that treatment as of yet. I’m a little fearful of such a high dose of doxy with the proheart. One reason being that he has coughed up some mucus a couple of times tinged with a little blood. Would it be safe to start his oral treatment? Thanks.

  18. Chris says:

    We had 2 dogs that wondered up on us last summer around May. One was an emaciated yellow lab mix & a shepherd-husky mix whom looked pretty healthy. The lab was the first to go to the vet in October as he wasn’t gaining weight & had chronic diarrhea. We learned he was barely 1yr old at time( luckily he was neutered) He was started on a special diet, given vaccines & started on proheart 6 as he was heart worm neg. He has done just fine & is a much healthier happier dog. Husky mix went to vet last month for neutering & vaccines & unfortunately tested positive for heart worms. He was given proheart 6 as preventative & the vet recommended the full fast kill method for treatment. There is no way possible we could follow that treatment plan as these dogs are live outside in the country & they are very active. Oral treatment with doxy 300mg a day for 30 days was recommended as a substitute. We have not started that treatment as of yet. I’m a little fearful of such a high dose of doxy with the proheart. One reason being that he has coughed up some mucus a couple of times tinged with a little blood. Would it be safe to start his oral treatment? Thanks.

    • Doc says:

      Hello, Chris and Patti,
      The “moxi-doxy” regimen that has been shown to be effective in some dogs, aka “slow kill”, has only been studied (and limited study) with the monthly Advantage Multi. ProHeart 6 and ProHeart 12 both contain the same medication as Advantage Multi, which is moxidectin. They might work the same and they might not. Monthly Advantage Multi has been shown to build up a more or less continuous blood level of the drug. The long-acting injections are believed to start with a higher level at first, and a lower level later. The timed-release formula is effective at preventing heartworm infection, but may not give the same blood levels as monthly Advantage Multi.

      The standard dose of doxycycline in these treatments is 10mg/kg twice daily for 30 days. Some investigators feel that 5mg/kg is just as effective. This is to suppress the Wohlbachia organism in the heartworm, making the worms smaller, weaker, easier to kill, possibly less antigenic when the dead worms shift position and hit a new section of artery downstream.

      A 66 pound dog is a 30-kg dog, so 10mg/kg would be 300 mg. The biggest problem I see with doxycycline is that it can make some dogs nauseated. It’s better if given with food, but a few just can’t take it. This is true whether you are giving any other medications or

      Doxycycline can be caustic if lodged in the esophagus, so it’s always good to be sure the dog takes a snack or a drink after taking the medicine.

      The reason that restricted activity is recommended after giving the melarsomine (Immiticide, Diroban) to kill the adult heartworms is that the dead worms move downstream and lodge in an artery too small for them to pass through. You don’t want a high blood pressure in that situation. So, no prolonged aerobic exercise. Dogs in the house are usually fine, leash-walking is usually fine. Running loose can allow prolonged increased blood pressure for hours. Not so fine.

      With the traditional treatment (which you have referred to as “fast kill”) you know the time frame when the worms will die, and how long it takes for the white blood cells to dissolve them out of the way. So you know when to restrict the dog’s activity. With the “slow kill”, you have no idea when that’s going to happen. If there are very few worms, you may never know it when it happens. Or you may cough up blood.

      With the “Fast kill”, we usually are sending home prednisone to help control the inflammation in those arteries, making it less likely that you would have enough of a blockage to cause arterial rupture.

      It’s a complex disease with a complicated treatment.

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