# How important is Heartworm medication??



## sjohnson322 (Jan 20, 2010)

Just out of curiosity, my friend a vet tech, told me she didn't think heart worm medication (heartguard) wasn't completely necessary. I have 2 healthy dogs, both from animal shelters and have given them their heartgurad on a monthly basis as long as I've had them. Since they live in a clean environment, and are not exposed to many other animals, I assume heart worm would be a very unlikely problem for us. I guess I am not totally educated on heart worm and the prevention of it. Is it a marketed drug that really doesn't serve that meaningful of a purpose besides $$$, or is it that big of a key to keeping a healthy dog?


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## Willowy (Dec 10, 2007)

Heartworm is transmitted by mosquitoes, so how clean the envionment is means nothing, nor does exposure to other animals (except mosquitoes, LOL). Where do you live? Some places just don't have a heartworm problem, but in other areas (such as the SE U.S.), any dog not on heartworm prevention meds WILL get heartworm.


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## xxxxdogdragoness (Jul 22, 2010)

I give mine a preventive as well, but its also a wormer wormer. It gets hooks & rounds we well I believe. Heartworm is not transmitted through direct dog contact, its passed from animal to animal thru the bite of an infected mosquito. Since I live in an area (east TX about 60mi west of houston) id rather be safe then sorry.


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## Lindbert (Dec 12, 2010)

If your dog can be bitten by a mosquito, your dog can get heartworm disease. Treating heartworm is expensive, painful, dangerous, and requires extended periods of inactivity (more or less crated almost all the time. Only walks to potty for a few weeks, restricted activity for MONTHS).

For me the cost of year round heartworm preventative is worth sparing my dogs from this misery. Heartworm disease isn't something to mess around with.


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## A&B (Mar 26, 2011)

Where I live mozzies are horrid. We have some lakes, creeks and rivers nearby and mozzies are a problem year round. 

I use Sentinel monthly, and I'm still refusing the yearly injection. Sentinel does fleas, intestinal worms & heartworm. Can't go past it, plus Batty LOVES the chews!


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## sjohnson322 (Jan 20, 2010)

We just moved from El Paso Texas to Georgia. A lot more bugs (mosquitos) here!


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## Willowy (Dec 10, 2007)

Well, you NEED it in Georgia or your dogs WILL get heartworm. In El Paso, not so much. Is your vet tech friend in GA or TX?


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## moluno (Apr 29, 2009)

It does depend on your area. We have a huge mosquito population here, and my dog spends a lot of time outdoors... I would be foolish to not give her heartworm preventative. It is a horrible thing to have to treat--really awful for the dog. 

There are areas though where heartworm is not an issue, and so in those areas prevention is not pushed on people.


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## sjohnson322 (Jan 20, 2010)

Is there a huge difference in the generic Iverhart compared to Heartgard?


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## Willowy (Dec 10, 2007)

sjohnson322 said:


> Is there a huge difference in the generic Iverhart compared to Heartgard?


Nah, it's pretty much the same stuff. In fact, if price is really an issue, you can use regular liquid ivermectin (the kind sold for livestock). I do like the convenience of having a broad-spectrum de-wormer in one monthly pill, but no denying the Ivomec is way cheaper.


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## sjohnson322 (Jan 20, 2010)

Is there a huge difference in the generic Iverhart compared to Heartgard, besides the obvious chewable? Does it have the same preventable effects?


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## kafkabeetle (Dec 4, 2009)

sjohnson322 said:


> Is there a huge difference in the generic Iverhart compared to Heartgard, besides the obvious chewable? Does it have the same preventable effects?


I've never heard of Iverhart, but there are a few other brands of heartworm prevention on the market. We use Interceptor because that's what our vet happens to carry and it prevents heartworm as well as a few other "worm" parasites. Oh, and btw, if Iverhart is a topical and not "chewable" I'd say it probably won't work.

We don't live in a high risk area (that I know of) but I still use prevention whenever the ground is thawed because it's so risky if they do get it. Treatment can take a long time and there's no guarantee your dog will make it through the treatment. On the other hand, we don't use flee prevention unless we're going camping or going somewhere flee-infested. There just aren't that many flees around here and if she does get a few on here Capstar kills 'em along with frequent baths. If I lived somewhere with more flees it would be worth my while to use prevention though.


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## Elana55 (Jan 7, 2008)

Willowy is right butr be sure to get the dosage right. Ivermectin is ivermectin. 

I would not risk not giving it. What it does is kill any larva before they become dangerous in size within 48 hours of giving the pill to the dog. The larva become dangerous after 30 days so you give the dose every thirty days and it kills any that might be there. It also will kill some species of worms. 

Lots cheaper than treating a dog for heartworm and a LOT less stress on the dog. Large kennels use the cattle injectable around here, but you do need to get the dose right.


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## sassafras (Jun 22, 2010)

Iverheart has the exact same ingredients as Heartguard, it's fine and a bit more affordable.


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## Legacy (Mar 9, 2009)

Florida here with mosquitos around even in the winter if we have a few warm days. My aunt's dog had heartworms and went through the treatment. It was very hard on the dog. It's Interceptor without fail for Shayna every month. (Shayna is an Australian Shepherd. There are breeds in the shepherd and collie lines that cannot have ivermectin unless genetically tested. Ivermectin can make them very sick or even kill them.) If your dog is one of these breeds, please research with your vet before giving him/her ivermectin unless they have already had it before!

Legacy


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## Fuzzy Pants (Jul 31, 2010)

I don't see how your friend could be a vet tech and not know how dangerous heartworms can be.


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## Labmom4 (Feb 1, 2011)

It depends on where you live. Ask your vet. We dont have it here (so.Calif.) and my vet says I dont need it.


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## FlashTheRottwuggle (Dec 28, 2009)

Iverhart is what my vet has me use. He and I don't agree on everything but he seems pretty insistent that the dogs be on preventative and their lives are too important for me to chance it.


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## xxxxdogdragoness (Jul 22, 2010)

Elana55 said:


> Willowy is right butr be sure to get the dosage right. Ivermectin is ivermectin.
> 
> I would not risk not giving it. What it does is kill any larva before they become dangerous in size within 48 hours of giving the pill to the dog. The larva become dangerous after 30 days so you give the dose every thirty days and it kills any that might be there. It also will kill some species of worms.
> 
> Lots cheaper than treating a dog for heartworm and a LOT less stress on the dog. Large kennels use the cattle injectable around here, but you do need to get the dose right.


Yeah that's the only thing about ivermec that scares me is not getting the dosage right be cause if I'm not mistaken, it can be dangerous to the dog if its not right, correct?


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## Willowy (Dec 10, 2007)

dogdragoness said:


> Yeah that's the only thing about ivermec that scares me is not getting the dosage right be cause if I'm not mistaken, it can be dangerous to the dog if its not right, correct?


Only if you overdose dramatically or have a dog with the mutation. Otherwise it's pretty well tolerated. Only a tiny amount is needed for heartworm prevention---much higher doses are used for mange treatment.


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## Charis (Jul 12, 2009)

I agree that heartworm is killer. I get a heartworm snap down every year right before bugs start coming out because I don't do preventative all year long. If there is snow on the ground - I don't give anything. Also I have heard (but I am not 100%) that a mild case of heartworm can be masked by giving preventative and thus delay treatment for the dog. Again - not real sure about that but either way I get the test before starting treatment back. 'Squitos are terrible here!


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## ThoseWordsAtBest (Mar 18, 2009)

I hope you inform your friend what dangerous advice she is giving out. Heartworm kills and that wasn't some evil agenda created to make money. 

Anyone have that heartworm map handy? It can't survive in mosquitos if the weather dips below 57 degrees and it maps out nicely what months of the year you need to be using protection. We are in Michigan, so 4-5 months are prime.


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## Northern_Inuit_Luv (Aug 26, 2009)

Here's a link with a map from 2007 http://www.heartwormsociety.org/pet-owner-resources/heartworm.html ...all I can say is I live near chicago and our rescue has had 7 heartworm positive dogs since August. To not prevent it could mean that my dogs could get it and spread it before I have a chance to heal them...we live in a very dog friendly neighborhood right around the block from a swampy forest area. If even one dog in this area caught it, I can promise you that there would probably be more shortly after. Not to mention, I'm the neighbor who is caring for a heartworm positive dog through her treatment...I make sure that the neighbors know so hopefully they take the warning and keep their dogs up to date. That being said, there's no way I could warn EVERYONE in the neighborhood...the same could be happening with someone in your area. Do you really want to take that type of risk?


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## Pai (Apr 23, 2008)

ThoseWordsAtBest said:


> Anyone have that heartworm map handy? It can't survive in mosquitos if the weather dips below 57 degrees and it maps out nicely what months of the year you need to be using protection. We are in Michigan, so 4-5 months are prime.


The dosing schedule maps are available here: http://www.tibetanmastiff.net/Heartworm.html
The maps are from a veterinary study into the seasonality of HW infection risk.



> If even one dog in this area caught it, I can promise you that there would probably be more shortly after. Not to mention, I'm the neighbor who is caring for a heartworm positive dog through her treatment...I make sure that the neighbors know so hopefully they take the warning and keep their dogs up to date. That being said, there's no way I could warn EVERYONE in the neighborhood...the same could be happening with someone in your area. Do you really want to take that type of risk?


Heartworm takes around *3 weeks* to mature inside the mosquito (if the mosquito survives that long and the temperature stays perfect -- if it ever drops below 57F the larva will die inside the mosquito) and then *4-6 months* for the larva to mature inside a dog's bloodstream to the stage where they attach to the heart and become dangerous and can no longer be killed by a simple dose of preventative. It doesn't spread instantly like wildfire, nor is it a health problem until the larva actually mature and enter the heart (months after infection). It has to be neglected for a LONG time before there's any risk to a dog's life. Heartworms are a very slow-progressing parasite.

As long as you're giving preventative properly there's no looming threat of some kind of 'epidemic' popping up anywhere other than the already-endemic southern states where it's warm enough year round to sustain the worm life cycle constantly. Nearly everywhere else, there's a massive larva and mosquito die-off every year which keeps the disease in check. 

And there's no need to live in constant fear of infection -- since 'HW preventative' doesn't actually _prevent_ infection, it just kills any larva that are _already_ present in the dog. What it 'prevents' is the larva growing into actual Heartworms (by poisoning them). The reason the 'once a month' rule was put into place was to make it easier for people to remember to dose the dog regularly; it's not actually medically necessary in most places. If you give a HW pill at _any_ time before the larva grow up (within 4-5 months of infection) they will die just the same as if you gave it the very day after the mosquito bit the dog. There's no need to wait that long, normally, but it just goes to show that there's no need to be scared of HW as long as you're on top of things.


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## sassafras (Jun 22, 2010)

Pai said:


> If you give a HW pill at _any_ time before the larva grow up (within 4-5 months of infection) they will die just the same as if you gave it the very day after the mosquito bit the dog.


This isn't strictly true, although in theory it is possible the drugs have diminishing effectiveness with the age/stage of the larvae. Skipping a single month isn't the end of the world but 4-5 months is way too long. The reason 30 days is recommended is that killing larvae after 30 days is somewhat inconsistent and also to give a bit of a buffer for people who may forget a dose here or there. 

Here are a couple of quotes from a veterinary site that unfortunately I can't link to as it is subscription only, but a bit more detailed:



> The macrocyclic lactone preventatives (Heartgard. Interceptor, etc) are very effective at killing third and fourth stage larvae, pretty good at killing young fifth stage larvae and not nearly as good at killing adults. To molt from L3 to L5 takes 67-80 days and so in theory these drugs should only need to be given every 2 months. However, in the studies that have been done the theory doesn't always hold up in practice and so a few can get through. Consequently, the recommendation is to give it monthly. Plus it's easier to remember to do it once a month.


(This is a reply to the above quote.)


> That's generally true, but the quickest that a molt can occur is about 48-50 days. And the drugs likely have a tapering efficacy as the larvae mature, so a late-stage L4 may not be the same as an L4 that has just molted from an L3 (ie within the first 5 days after innoculation).
> 
> In endemic areas, monthly prevention is essential. Given that 80-90% of clients have incomplete compliance with HW prevention (whether intentionally, or unintentionally), giving the drug monthly reduces the potential for "missing a dose". Some people in very endemic areas, such as mississippi river valley are even giving the drug every 2 weeks.


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## Willowy (Dec 10, 2007)

In the latest issue of The Whole Dog Journal, they said that there's been a recent spate of dogs who ARE on preventive meds (supposedly monthly) testing positive for heartworm. They don't know if the microfilarae are becoming immune to ivermectin or what. Dosage does not appear to be a factor. So they amended their recommendation of giving the meds once every 45 days to doing it once a month as the medication manufacturer might pay for the treatment if you follow their guidelines. Not sure if they think giving it more often might make any difference.


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## sassafras (Jun 22, 2010)

Willowy said:


> In the latest issue of The Whole Dog Journal, they said that there's been a recent spate of dogs who ARE on preventive meds (supposedly monthly) testing positive for heartworm. They don't know if the microfilarae are becoming immune to ivermectin or what. Dosage does not appear to be a factor. So they amended their recommendation of giving the meds once every 45 days to doing it once a month as the medication manufacturer might pay for the treatment if you follow their guidelines. Not sure if they think giving it more often might make any difference.


Yea, I've heard talk of that coming up from the deep south. The most current speculation I've heard is that with such a huge exposure to mosquito bites in some areas, that even if less than 1% of microfilaria survive a dose of preventative it's going to add up. That's why some people are giving every 2 weeks. But it's definitely concerning and something that needs study.


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## RubyFeuer (Mar 30, 2010)

A&B said:


> Where I live mozzies are horrid. We have some lakes, creeks and rivers nearby and mozzies are a problem year round.
> 
> I use Sentinel monthly, and I'm still refusing the yearly injection. Sentinel does fleas, intestinal worms & heartworm. Can't go past it, plus Batty LOVES the chews!


They have an injectable heartworm preventative?


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## Pai (Apr 23, 2008)

RubyFeuer said:


> They have an injectable heartworm preventative?


Yes, ProHeart6. After it was released to the public it was discovered that it has risks for some serious side effects (including liver damage), so it was recalled and made 'prescription only'.



> Skipping a single month isn't the end of the world but 4-5 months is way too long. The reason 30 days is recommended is that killing larvae after 30 days is somewhat inconsistent and also to give a bit of a buffer for people who may forget a dose here or there.


I'm not recommending waiting that long, of course. But from what I understood, it was found in a 1988 study that waiting as long as 4 months between doses was still 95% effective. Which IS a reduction, but not by that much. However, the fact that the current medication appears to not be 100% effective anyway makes that entire thing a guessing game that's not smart to play, anyway. 

If it's true, however, that the larva are developing a resistance to the drugs, it just shows that overdosing with them when not needed is not a good idea, either. This is how we've gotten superbugs that are resistant to current antibiotics -- by people using them all the time when it wasn't necessary.


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## RubyFeuer (Mar 30, 2010)

I ended up reading about that a little bit after I asked lol. Doesn't sound worth it I'd rather stick to the oral medications.


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## Mr. V (Jan 28, 2010)

Pai said:


> I'm not recommending waiting that long, of course. But from what I understood, it was found in a 1988 study that waiting as long as 4 months between doses was still 95% effective. Which IS a reduction, but not by that much. However, the fact that the current medication appears to not be 100% effective anyway makes that entire thing a guessing game that's not smart to play, anyway. .


More recent studies that are soon to be published (done at my school I might add ) have shown that infective L3 larvae (which are susceptible all preventatives) can develop into L4 stage larvae within 3-12 days and (susceptible to some preventatives, but not as much) can prematurely enter the pulmonary artery above the heart and remain there neary the capillary beds of the lungs. The studies show that these larvae are NOT affected by preventative and are allowed to live there until they develop into L5 larvae (not affected by any preventative that I know of) and then into mature adults where they migrate back down to the right side of the heart and set up shop.

It's been documented that these guys can develop into an L5 in as little as 45-70 days. Because of this, I will always stick to the once monthly rule and not try to get too clever with my dosing scheme just to save extra $$$.

In my opinion, the best information on heartworms can be found at www.heartwormsociety.org. These are the experts on the cutting edge of heartworm research.

On the topic of resistant bacteria -- I have a major hang up with this subject and it really grinds my gears. The problem isnt' the owners, it's their foolish vets that keep prescribing antibiotics without doing proper culture and susceptibility testing. Instead of starting out with something more simple like cephalexin, they just jump right to what they call "the big guns" and go blasting away without knowing what the nature of the infection is. It's dangerous and dumb. Perfect example: my patient today had a MRSI (resistant Staph infection) because it had been on round after round of cephalexin, clindamycin, and of course baytril (enrofloxacin). Never once was the dog given appropriate dosage or length of therapy (just stick em on 14 days and hope for the best right!?!?). Now we've cultured the dog and she's resistant to every single antibiotic except one called chloramphenicol which still isn't even giving us the results we want. GREAT!!! What's the moral of this little rant of mine? Do not allow your vet to prescribe tons of antibiotics after the first round fails. Insist on culture and susceptibility! May cost you a tad more to start off with but better than years of failure and resistance. Ok, im done.


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## Pai (Apr 23, 2008)

Not wanting to use more pesticides on a dog than necessary is not just to save money. Using more drugs when less would do results in more being spent, yes, but thats just because nothing is free. It's not a virtue to spend money unnecessarily, nor is it a sign of responsibility. Using more drugs is not an automatic virtue, either. A lot of people's fears about HW are based on completely wrong beliefs about infection and how it works. That's not a good way to make a proper medical decision. It will not instantly sicken/kill a dog or spread an epidemic around the neighborhood -- it's not ebola. In many states, the risk of infection at all is small, because the temperature drops kill the larva inside the mosquito before it even can enter a dog (if the mosquito doesn't get eaten or swatted first). There is no HW infection without the mosquito living two solid weeks in the proper temperature. Those are very relevant facts of the disease risk, and should be known by people.

In my own state, which has a population of about 5 million dogs, there were like 4 cases in my area over _7 years_ (using Idexx's own data -- and only 80 cases statewide). My own vet has never seen a case in 20 years in her own practice. I personally give my dogs monthly doses from July to October; just to make it clear that I'm not saying people should not give monthly doses when it's appropriate. But the operative word is 'appropriate'. For some people, that DOES mean year round. No disagreements there.

And to be clear on something else, I feel the 'more is better' attitude in regards to drugs is motivated just as much by well-meaning intentions as it can be by economic self-interest. Nobody wants our pets to get sick or infected. But it's not so simple as in 'more drugs = better outcomes'. That's been made clear even in human medicine. There is no side-effect free option of putting dogs constantly on deworming chemicals (of any kind) year round, regardless if there's an actual risk of the worm or not. That's not smart medical care, that's laziness and/or paranoia.

I'd love to get links to your school's research when it's available, even just the abstracts.


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## Lindbert (Dec 12, 2010)

Mr. V said:


> On the topic of resistant bacteria -- I have a major hang up with this subject and it really grinds my gears. The problem isnt' the owners, it's their foolish vets that keep prescribing antibiotics without doing proper culture and susceptibility testing. Instead of starting out with something more simple like cephalexin, they just jump right to what they call "the big guns" and go blasting away without knowing what the nature of the infection is. It's dangerous and dumb. Perfect example: my patient today had a MRSI (resistant Staph infection) because it had been on round after round of cephalexin, clindamycin, and of course baytril (enrofloxacin). Never once was the dog given appropriate dosage or length of therapy (just stick em on 14 days and hope for the best right!?!?). Now we've cultured the dog and she's resistant to every single antibiotic except one called chloramphenicol which still isn't even giving us the results we want. GREAT!!! What's the moral of this little rant of mine? Do not allow your vet to prescribe tons of antibiotics after the first round fails. Insist on culture and susceptibility! May cost you a tad more to start off with but better than years of failure and resistance. Ok, im done.


THIS.. sadly so many of our clients insist we're just trying to take their money and ask "can't you just try another med and see if it works?" and when we explain WHY we don't want to do that and would rather do a C & S, they pull out the "MY physician doesn't have to culture anything, he gets it right the first time!" line. This especially angers me when it's something like chronic otitis media and the dog is staggering around and feeling horrible when I know giving the right antibiotic right away without waiting to fail a few antibiotic trials will dramatically shorten the time the dog is feeling ill.

And then I bang my head against the wall.


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## Pai (Apr 23, 2008)

On the subject of MRSI, on one dog blog I visit they had no luck with any antibiotic, but medical-grade honey was actually effective. Just figured you might be interested into looking into that, if you hadn't already (as a last-ditch thing if nothing else works, in any case). Here is the post about it.



> THIS.. sadly so many of our clients insist we're just trying to take their money and ask "can't you just try another med and see if it works?" and when we explain WHY we don't want to do that and would rather do a C & S, they pull out the "MY physician doesn't have to culture anything, he gets it right the first time!" line.


As much as it may seem like I think everything is the fault of vets, I actually do lay the blame at the feet of many owners as well. People wanting quick, convenient solutions to everything are at the root of a lot of problems both in human and animal health care. People don't think about the long term effects, or weigh the risk vs benefit of different strategies. Perhaps it's easier to do with animals since they don't live as long as we do. Either way, it's disheartening.


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## Lindbert (Dec 12, 2010)

There are so many things I would love to change about mainstream veterinary medicine, however that would be another topic for another day. 

Such as making a very affordable ivermectin only preparation for heartworm preventative widely available. Obviously the medication is effective and it is inexpensive (look at ivomec,) yet we still do not have a product marketed and available for that indication. I would rather see more dogs avoid heartworm treatment and be on a ivermectin only preventative over having additional protection from rounds and hooks in the typical more costly ivermectin/pyrantel preperation.


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## cshellenberger (Dec 2, 2006)

Lind, even the Ivermectin/Pyrantel prep is overpriced. Take a look around any feed/tack store at what it costs to worm a horse or livestock vs what it costs to have a dog on preventive. That a dogs meds is more expensive than an animal 10x it's size is ridiculous!


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## Lindbert (Dec 12, 2010)

It is ridiculous and there is absolutely nothing to justify WHY they are charging that kind of money. Is it for the super-palitable chewable formulation? I think not.. they were giving away placebo chews to promote heartgard by the caseful a couple of years ago. Is it for the pretty box? Is it because Merial is using the money to fund less toxic, more affordable, and better tolerated heartworm treatment? Nope.. Immiticide is still the standard of treatment and it is painful, dangerous, and EXPENSIVE. Where exactly does the money go?!

I just called a pharmacist friend of mine to find out what Merck charges for the human preparation of ivermectin. Even that's considerably less than Heartgard!


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## Mr. V (Jan 28, 2010)

Pai, I can not yet provide that as there is no link. This is stuff he hasn't even written yet I don't think or is in the process of writing it. The guy that did the research was just talking about it during a general talk on hw prevention during a lunch n learn thing for students and he had thrown in some quick data into his powerpoint. I'll check though as I'm sure I'll see him cruising the hospital this week. It's awesome to me that I am able to encounter stuff that won't even hit the text books for 5 or 7 years as I casually walk through the halls. Things are always changing and it's kinda exciting.

And, I did not mean to imply that everyone who wants to decrease their hw prevention frequency is doing it for money. It's the motive for most that I encounter, but, I know there are many out there that have your concerns as well. Now that I go back and read what I wrote, it does sound worse than I intended. My bad.

If you're curious, in general, about times when larvae molt and so on and so forth, you can find it on the heartworm society website under the veterinarian resources tabs. The ones for owners are just general talk, no specifics.


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