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Which Heartworm Preventative Is Safe For My Border Collie?

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I will be asking our vet about my concerns next visit soon, and as far as what was said about competitors it would be unprofessional for them to post false info about other companies meds, but I guess that doesn't mean it might not happen.



I am not sure what you are asking. HW pills are not a preventative, they are a treatment. That is part of why many people take issue with giving it or giving it year round. You are treating for something that tr dog can't get (in the winter months here there are no mosquitoes ). In the south your temps are higher, this is why many people give a pill monthly for the whole year or most of the year. What are you referring to about doses being higher or more toxic?



Gary I think you need to stop looking for problems where there are not any. Many people have dogs killed from choking on kibble or from toxic commercial dog food. You can find stories online to comfirm any concern you have about anything. It doesn't mean it will happen to your dog. Any medication can cause side effects, millions of dogs take HW pills and do just fine on them. Dont go looking for sad stories just to freak yourself out. I think your dog is more likely to be struck by lightening than die from the HW pills you give her. Did you read the link I posted and all the comments on Terriermans blog? No drug is 100% effective or safe- just decide on a brand you like and go with it. Every time I see a house fire on the news I start to worry that my house will burn down. Sometimes you need to just turn the news off and turn google off. :)



I don['t know about other areas of the country but I do know that Kansas City and south are all high danger areas for heartworm. I wouldn't take the risk of not having my dogs on heartworm preventative. The whole southeast is high risk.


I did read something interesting about first hand reports of problems with heartworm meds - sometimes the competitors put those stories out. You really need to check with your vet and find out what the safest thing to do is. And they will also be aware of problems.


When my dog was having problems with her auto immune disease my vet had her on Revolution because it wasn't as stong as some of the others.

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I have a few thoughts to add to this discussion.



Heartworm preventatives prevent a heartworm infection by killing off microfilariae before they can mature into heartworms; dogs still have a microfilariae infection. The duration of effectiveness of the monthly preventatives is not related to the drug but to the lifecycle of the microfilariae maturing into heartworms.



All heartworm preventatives are in the same class of drug; they all work the same way. Just because one drug has a lower minimum effective dose (microgram/lb body weight) does not mean it will be less likely to cause an adverse reaction than another. Each drug has a unique minimum effective dose (microgram/lb body weight). The key number to compare is the difference between the minimum effective dose and the dose at which adverse reactions occur; or the multiple of the minimum effective dose at which adverse reactions occur. This gives the safe working range for each drug; the wider the working range the safer the drug.



Heartworm preventatives are not just the active drug; they all contain other ingredients (a drug formulation). Some dogs can and do react to these other ingredients; just because a dog reacts to one of these drug formulations (given within the safe working range) does not automatically mean the dog reacted to the active drug. The dog could have an underlying condition that predisposes it to react to one of the other ingredients. This phenomenon occurs with vaccines which are also complex formulations with many ingredients.



There is evidence that in some regions the monthly heartworm preventatives are not 100% effective. This may be related to the percentage of mosquitos that are infected with microfilariae, the level of infection of microfilariae in infected mosquitos (dose of microfilariae being given to dogs), or the genetics of the microfilariae (or a combination). Studies continue as to the source(s) of the loss of effectiveness.



As someone else pointed out, you can treat with monthly preventative to kill of microfilariae or you can gamble your dog won't get bitten by an infected mosquito and then have to treat with a much more dangerous drug and the risks associated with killed heartworms being pumped through your dog's heart. If your dog is one of the few that has adverse reactions to one monthly heartworm preventative (one manufacturer's drug formulation), work with your vet to find another (different drug formulation) to which your dog does not have adverse reactions.


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  • 1 month later...

One of my border collie/jrt mixes seems to have a sensitivity to heartworm meds. He has become quite ill with at least 3 different ones. I did have some Sentinel leftover from when I was hoarding it and thankfully he is ok with it. When I run out I will have to decide what to try next. His great-grandfather almost died from heartworm meds (they believe he does have a ivermectin sensitivity). He no longer gets HW meds but he is also in a low risk area. VA is a higher risk area but will do what I have to do... it was also suggested splitting the dose into 2 different doses (am and pm).


With any meds there is a possibility of a reaction. You just have to decide how to handle it and you may have to go through some trial and error to find a solution.


Trip's reactions: fever, diarrhea, lethargy, etc... so yes he has a bad reaction but I will continue the trial and error when it is time. I will just keep an eye on him when he is given the meds.

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Thank you Mark for adding some well-reasoned comments to this discussion.


If you live in the south, you are in essence playing with fire if you don't use HW preventives. As Mark points out, there are other ingredients that can cause reactions.


I also agree with whoever it was that cautioned against taking everything you read on the internet as gospel. It's anecdotal evidence. I'd think that if thousands of dogs had died after being given Trifexis, it would be in the scientific literature.


Humans, being what they are, will often try to relate cause and effect, and usually they will assume the cause is the last thing they did (I ate cabbage and got sick later therefore the cabbage must have made me sick). Cause and effect doesn't work that way.


I gave my 10 week old puppy Trifexis and she's still alive and kicking. I've used it on the LGDs without incident. Like Liz, the biggest caution I've ever seen was the possiblility of vomiting, which of course means that the meds might not have been absorbed, leaving the dog unprotected.


I also use Comfortis for fleas. I use ivermectin (egads! Haven't killed a dog yet.) There aren't a great number of truly new HW or flea/tick preventive chemicals, just new combinations.


I know we've had this discussion before, but I'll repeat it: each person has to determine what risk vs. benefit scenario they are comfortable with. I have an epileptic dog. I still give her HW preventive and use flea/tick meds on her, because I personally believe that treating her for HW or TBDs is more likely to cause problems than using the preventives. If I could correlate seizures with any drug use, then of course I'd try to find some other means of prevention or control.


Nothing is 100% safe--that's why even the TV ads for various medications provide a long list of possible side effects for the drug in question.


If I were you, living in SC, I'd most definitely be using HW preventive year round. If you're lucky enough not to have fleas or ticks, you could skip that, but chances are, given your location, that you'll need those preventives too. You can always try to use the absolute minimum dose that is effective, but that would probably be something I'd do with flea/tick preventives rather than HW preventives.



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Luckily my vet clinic is carrying Sentinel again. Sadly Interceptor isn't back on the market but I'm stocked up on it until Christmas. My older Border Collie Rose cannot take ivermectin based products any more due to her eye condition. The opthamologist says he's seen Border Collies and other collie breeds showing similar eye conditions after exposure to ivermectin. She is tentively diagnosed with Immune Medated Retinopathy/SARDS and is on treatment with immunosuppressive drugs. Although studies have shown Ivermectin to be safe at the levels found in Heartguard I am reluctant to use it anymore on any of my dogs. Since the very expensive (argh!) opthamologist doesn't want any BC's (and Rose specifically) on Ivermectin products I no longer feel comfortable using it. But I think it's important to realize that all drugs can cause side effects and that each individual may respond differently to these chemicals. I have known a few Border Collies that had seizures after getting Heartguard but it seems safe in others. I personally avoid using any drugs until they have been on the market long enough for some safety data to be available from the population at large.

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  • 8 months later...

Thanks For Giving great information.

Interceptor is the ONLY safe heartworm prevention medication for Collies, Collie-mixes, Shelties and Sheltie-mixes. This is because Interceptor does not contain the drug ivermectin, which is known to have deadly effects in these and some other breeds. Heartworm prevention is easy.

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4 hours ago, drpriyaverma said:

Thanks For Giving great information.

Interceptor is the ONLY safe heartworm prevention medication for Collies, Collie-mixes, Shelties and Sheltie-mixes. This is because Interceptor does not contain the drug ivermectin, which is known to have deadly effects in these and some other breeds. Heartworm prevention is easy.

All heartworm preventatives (at the prescribed dose) are safe in dogs with this mutation regardless of breed according to WSU


All heartworm preventatives are in the same class of drug (see the link above).


  • Selamectin, milbemycin, and moxidectin (antaparasitic agents)- Similar to ivermectin, these drugs are safe in dogs with the mutation if used for heartworm prevention at the manufacturer’s recommended dose. Higher doses (generally 10-20 times higher than the heartworm prevention dose) have been documented to cause neurological toxicity in dogs with the MDR1 mutation.

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