This is an article that I found on VerernaryPartner.com  The DVM's that I work with refer our clients to this web site a lot.  It has reliable information that the average Joe can understand.


THE PET HEALTH LIBRARY
By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com 
 

     
Preventing Heartworm Infection in Dogs (Chemoprophylaxis)

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Brands:

Ivermectin-based Products: Heartgard, Heartgard Plus, Iverhart Plus, Iverhart Max, Tri-Heart Plus
Milbemycin-based Products: Interceptor, Sentinel
Selamectin-based Products: Revolution
Moxidectin-based Products: Advantage Multi, Proheart6

Heartworm preventive medications are used to periodically kill larval heartworms that have managed to gain access to the dog's body. At this point, the products available are intended for monthly use. This means that they kill all the heartworm larvae (stage L3 and L4) that have accumulated in the past month each time they are given. Some products offer the ability to kill older larvae which helps keep the pet protected in case someone is late giving the heartworm preventive medication at some point. There are presently many choices, both topical and oral, plus, while the subject of this page is canine heartworm prevention, all the products discussed have feline formulations.

Ivermectin-based Products:
Heartgard, Heartgard Plus made by Merial
Iverhart Plus, Iverhart Max made by Virbac
Tri-Heart Plus made by Schering Plough 

The approval of ivermectin in 1987 represented a huge breakthrough in heartworm prevention. Preventive medication for the first time could be given once a month instead of every day. These monthly medications utilize an extremely low dose of ivermectin that is adequate to kill any L3 and L4 larval stages inhabiting the pet's skin tissues at the time the medication is given. In other words, infection takes place but is halted every month when the medication is administered.

If Given to a Heartworm Positive Dog by Accident 

In most cases, no reaction of any kind occurs when an ivermectin-based heartworm preventive is given to a heartworm-positive dog.

In fact, giving an ivermectin-based heartworm preventive to an infected dog is the first step in heartworm treatment. Ivermectin kills the developing larval worms and clears the circulating microfilariae, thus rendering the dog unable to spread its infection and minimizing the number of adult worms to be killed in the second phase of treatment when the adult worms are specifically addressed.

If the larval worms die too quickly, a shock-like circulatory reaction can occur so for this reason the American Heartworm Society recommends that the first dose of ivermectin be given under veterinary supervision. This allows the dog to be observed for several hours following the oral dose in case of trouble. That said, in most cases no reaction of any kind occurs and the larval worms are cleared without event. This does mean, however, that giving this product to a dog with heartworm will kill all circulating microfilariae and the dog will test erroneously heartworm negative by Difil or Knott testing. (ELISA test kits should still be accurate). In addition to killing microfilariae, ivermectin will also suppress reproduction in the adult female worms and shorten the overall life span of adult worms. Ivermectin does not kill adult heartworms (just the immature ones) although, as said, it cuts their life expectancy.

The Reach Back Effect

There is also a phenomenon called the reach back effect. This means that if a dog goes off heartworm preventive medication for a prolonged period (four months was the time tested), re-starting preventive could still curb adult heartworm infection in the heart and pulmonary arteries. In the 1988 experiment by Atwell, dogs who went off heartworm preventive for four months and then restarted with ivermectin had 95% fewer adult heartworms than dogs who went without ivermectin, although it should be noted that some heartworms were still able to establish infection. This means that if you skip several doses of ivermectin accidentally, it is still worth picking up where you left off.

Other Parasites Covered

Ivermectin at the heartworm preventive dose is not strong enough to kill common intestinal parasites. Because of this fact, pyrantel pamoate, a dewormer, was added to cover hookworms and roundworms in the original Heartgard product. As other ivermectin-based products have entered the market, these have also added pyrantel pamoate to extend the spectrum of protection.

Whipworms are not covered by any of the ivermectin-containing products at this time, but in order to remain competitive in the market, manufacturers may pay for treatment for whipworm infections acquired while their product is administered. The products containing both ivermectin and pyrantel pamoate are Heartgard Plus, Iverhart Plus, and Tri-Heart Plus. Iverhart Max includes both pyrantel pamoate and praziquantel so as to cover tapeworms as well.

Breed Sensitivity 

There are breed-related sensitivities with ivermectin (i.e. collie-related breeds have some difficulties) though at the low doses used in the prevention of heartworm disease are not a problem for any breed.

Use of Large Animal Products 

It is neither safe nor legal to obtain large animal ivermectin products for use in dogs for heartworm prevention. Discussions of doses have circulated around the Internet and in other sources advocating the use of highly concentrated ivermectin formulas for heartworm prevention in dogs. These doses are not comparable to the miniscule doses in licensed heartworm preventive products and using them represents an element of gambling. Large animal ivermectin products are vastly more concentrated than those meant for dogs and it becomes problematic to dilute them properly. Even small doses of these products are unnecessarily high and if they are inadvertently given to a sensitive individual, death can result.

That being said pet owners are going to do what they feel is right for the health of there pets.  Just like a parent would for there child.  I just wanted to share the info and the website.

Thanx for reading,
Amanda

watch it , she barks loud and swings a big STICK!!! ..... lol

I only use the stick when Jason gets out of line.  lol  Thanx for bringing that up, Eric!


I didn't mean to ruffle any feathers or hurt anybody's feelings.  God knows I have no buisness judging anyone else.  I am not perfect.  I just have a big heart for animals.  Thanx for reading. 

So if you use ivermectin at a high dose to worm your dog and they already have heartworms it will kill all the heart worms at once therefore it may cuase a blockage in the heart or lungs.  I suggest getting a heartworm test done at your vet before starting ivermectin  just to be safe and also have them calculate a dose for you.  Because the mounthly dose is quite small.

It really bugs me when I see a post under the dog trade about owners selling/traiding dogs that obviously need vet care or need to be retired.  When you take on a dog it is your responsiblity for the rest of its life.  You don't get rid of it because it is broken.  And shame on you for wanting to sell your problem to the next guy.  Don't try to sugar coat the dogs abilities either.  If he is what you say he is why do you want to get ride of him?

Nobody wants your 3 legged dog.  You need a spanking!!!

Sorry just needed to vent.  Does anyone else feel this way?