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Heartworm Preventitive Question


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#1 Maralynn

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Posted 25 July 2005 - 11:07 AM

I was recently reading on another board that heartworm preventitive really only needs to be given every 45 days instead of every 30 days. The only reason for giving it every 30 days is that it is easier for people to remember.

Has anyone else ever heard this?

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#2 M.L.

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Posted 25 July 2005 - 12:02 PM

My holistic vet has told me to give my dogs their heartworm meds every 45 days rather than every 30 days.

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#3 juliepoudrier

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Posted 25 July 2005 - 01:20 PM

Yes, it's true. BUT, as I understand it at 45 days you are pushing the preventive to its effective limits. So while the every 30 days thing is indeed more convenient for people to remember, the greater risk is that at 45 days you're not leaving yourself any margin of error if the preventive is not as effective at the outer limits of the time range.

Not the best example, but it will make the point. Say your doctor (or anyone else) told you that birth control pills (sorry if this offends anyone) really don't need to be taken once every 24 hours and that you could save money if you took one every 36 hours, as the hormones remain in your bloodstream for that long after taking a pill, but of course the 24-hour time frame is easier for folks to remember so that's what we do. Now the doctor can't guarantee you that between hours 24 and 36 you have the EXACT SAME protection as you have from hours 0 to 24. Would you want to take that risk?

Most preventives work by killing infestation that has occurred in the time period preceding the dose of preventive. So the preventive is working by killing what's already there. If it's nearly completely effective at killing when given every 30 days and you don't have plenty of research to support that it's equally effective at killing everything that has entered the bloodstream in the preceding 45 days, is it worth it to take the chance?

So instead of going on hearsay from this board or any other, I would do some research and see if scientific studies exist to support the belief that giving HW preventive every 45 days is as effective as giving it every 30 days. If I found that the research supported the 45-day regimen and after discussing it with my vet, then I might consider changing my HW prevention regime.

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#4 BigD

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Posted 25 July 2005 - 02:20 PM

Just read all of Miztiki's heart-felt posts of worry and concern about Boyden testing positive for HW. Would you want to go through that?

Personally, I'll do the 30 days because I DON'T want to put my dog through it and I also know that I'm usually a few days late giving the pill anyway.

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#5 Maralynn

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Posted 25 July 2005 - 03:32 PM

Don't worry - I'm not saying I'm trying it! Besides, the first of every month makes it easy for me to remember! And I like having the "grace period".

I had just never heard it before, and was curious to hear others opinions on it.

Also, my family lost a dog in part to heartworm. She tested positive at 14 years old. She also had a few other health issues making treatment not an opption. I'm not messing around with heartworm.

Mara
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#6 Pipedream Farm

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Posted 26 July 2005 - 02:12 AM

Originally posted by Maralynn:
I was recently reading on another board that heartworm preventitive really only needs to be given every 45 days instead of every 30 days. The only reason for giving it every 30 days is that it is easier for people to remember.

Has anyone else ever heard this?

Yes I have read this on several Vet websites. Based upon my reading the 45 days stem from two processes: the rate of clearance of the preventive and the lifecycle of the microfilariae=>adult worms. I have not been able to relocate the Vet info site where the 45 day duration is explained but it is listed in the table Heartworm Preventive Comparison.

One side note:

All commercially available heartworm preventives act by wiping out the freshly delivered L3?s and the L4?s living in the skin. The Heartgard products are also able to kill the younger L5?s.

Source: Heartworm - The Parasite

This means that these drugs kill the microfilariae when initially delivered then are cleared by the body over a period of time (a few days). New microfilariae can then be introduced and the drug must be readministered to prevent these from maturing to adults.

Mark
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#7 Pipedream Farm

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Posted 26 July 2005 - 02:22 AM

I typically am a couple of days late giving the dogs their heartworm preventive. I know I am still safe being a few days late. If I waited 45 days and was my typical forgetful self, I wouldn't feel so confidant.
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#8 Wendy V

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Posted 26 July 2005 - 07:34 AM

I have given HW preventative every 45 days for several years, with no ill effects. I also give my epilepic dog a below normal dose of HW treatment, again, with no infestation.

Since a mosquito has a flying range of only 2 miles, heartworm infestation rates can vary much for different locals. Your vet would bve able to tell if your area is at high risk or not and then you can made your own treatment choice from there.

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#9 Rave

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Posted 26 July 2005 - 08:08 AM

It depends on the type of preventative you give!! I recently talked about this with a vet friend, who told me Heartguard lasts longer than Interceptor. Said she wouldn't feel comfortable going more than a couple days past 30 for Interceptor, but said she goes longer than that for Heartguard. Talk to your vet before you attempt to do anything like this, especially if you're in a mosquito-prone area!

#10 Kelliwic Border Collies

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Posted 06 August 2005 - 10:44 AM

I have been avoiding using Heartguard for my dogs due to the Ivermectin. From the research I've done, I haven't yet read that Border Collies are specifically identified as a breed with the gene that could cause a fatal reaction to ivermectin, but since related breeds are affected, I would rather be safe than sorry.

I thought it was only ivermectin that the mutant gene reacted to (as far as HW preventative goes) and so thought I'd be okay using Interceptor, but recently I read on a web site that the affected dogs may also react to other HW meds, such as the millbemycin oxime in Interceptor, and the active ingredient in one of the other popular preventatives (I forgot which one).

Has anyone else heard that the gene reacts to most HW preventatives? Or is the general research at this point showing an ivermectin-specific sensitivity?

Thanks for any input!

#11 Denise Wall

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Posted 06 August 2005 - 11:39 AM

The mutant MDR1 gene is defective in all drugs in the avermectin class, including the one used in Interceptor. I contacted the people who do the gene test just a couple of weeks ago and there have been no ivermectin sensitive border collies identified by the gene test in over 300 dogs tested so far.

Check out this web page for more info.
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#12 Kelliwic Border Collies

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Posted 06 August 2005 - 01:55 PM

Denise, thanks, that's one of the pages I have bookmarked. I'm glad that so far BCs appear safe, but how would a person know what drugs are in what class? The drug used in Interceptor is not specifically mentioned on the problem or potential problem lists on the vetmed page, so I wouldn't have known they were classed the same.

I found another page that lists some of the most commonly used (HW prev) drugs: HeartGard (ivermectin/pyrantal), Revolution (selamectin applied topically), Interceptor (millbemycin), and Sentinal (milbemycin/lufenuron).

Curious for more knowledge...thanks!

PS: Could it be possible that different breeds might have a different mutant gene? Ie, could BCs have a gene that is not being detected by the currently available test? Not trying to create a panic amongst BC owners, just wondering of the liklihood.

#13 Denise Wall

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Posted 06 August 2005 - 02:52 PM

All the heartworm meds are some type of avermectin.

PS: Could it be possible that different breeds might have a different mutant gene? Ie, could BCs have a gene that is not being detected by the currently available test? Not trying to create a panic amongst BC owners, just wondering of the liklihood.

It's not just that the mutant MDR1 gene has been undetected. There are no confirmed reports of border collies having the ivermectin sensitivity.

It's certainly possible that there's more than one mutation. However, as far as I know (and I have looked into it recently), the MDR1 mutant gene has been found in all of the breeds reported to have ivermectin sensitivity.
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#14 Kelliwic Border Collies

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Posted 07 August 2005 - 07:38 AM

Good news!

Thanks again!

#15 books

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Posted 15 August 2005 - 04:32 AM

Has anyone read anything about bc's actually having this gene? I found this site and there is a note that some bc's have recently been found to have the MDR1 gene. http://www.vgl.ucdav...projects/mdr1b/

#16 Rave

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Posted 15 August 2005 - 04:48 AM

I noticed on the website Denise linked to that the ingredient in Imodium has been reported to cause problems in dogs with the MDR1 gene. I'm curious if this means that a dog who has a reaction to Imodium should be tested for ivermectin sensitivity? And if a dog does not have a reaction to Imodium, does that automatically mean they do not have an ivermectin sensitivity?

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#17 Pipedream Farm

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Posted 15 August 2005 - 05:10 AM

Originally posted by books:
Has anyone read anything about bc's actually having this gene? I found this site and there is a note that some bc's have recently been found to have the MDR1 gene. http://www.vgl.ucdav...projects/mdr1b/

I would like to have this Note confirmed by WSU Veterinary Clinical Pharmacology Laboratory. Who knows how reliable the "internet reports" are.

I have emailed WSU and have requested confirmation of this "note".

Mark
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#18 Valhalla

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Posted 15 August 2005 - 08:19 AM

Originally posted by Denise Wall:
There are no confirmed reports of border collies having the ivermectin sensitivity.

Denise, since there are no confirmed reports of BC's having the ivermectin sensitivity, would you say it is safe to use the cattle Ivermectin injectable as an oral dose for heartworm preventative in BC's? A vet told me the preventative dosage is 1/8th cc per 55 lbs or 1/16th for 27.5 pounds. I have used oral ivermectin for my LGD for years, but have not used it on my BC's yet.
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#19 Denise Wall

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Posted 15 August 2005 - 08:38 AM

Hi,

Just ran through and saw this. Here's a general reply.

Important points to remember

1) The normal dose of ivermectin used for prevention of heartworm in products such as Heartguard (6 micrograms/kg) is not documented to cause the toxicity associated with this mrd1 mutation in collies or any other dog. It is only when higher doses are used, often by people mistakenly thinking the cattle/sheep dose is appropriate for dogs, that toxic symptoms appear in susceptible dogs.

2) Any of the avermectins, the class of chemicals ivermectin belongs to, are capable of producing the same toxicity in affected dogs when used at high doses. The commonly held belief that heartworm preventives such as Interceptor are safer than Heartguard is incorrect. Both products are safe at the low dose used. However, there are confirmed reports that moxidectin, which is used in the six month injectable for heartworm prevention, has caused neurotoxicosis in susceptible collies.

3) Any breed of dog can suffer from toxicity and death from ivermectin and the related class of drugs if they consume high enough levels to penetrate the blood-brain barrier. Levels of ivermectin shown to cause toxicity in beagles, a breed that does not have the mdr1 mutation are 2.5 - 40 mg/kg which is greater than 200 times the therapeutic dose.

Special considerations for farm dogs

An important consideration not everyone is aware of is that farm dogs often consume ivermectin or other avermectins in the manure from recently treated stock. Merck reports an apparent half-life for ivermectin of 1-1.5 weeks in sheep manure from sheep wormed with the standard drench dose of 200 micrograms/kg. They also estimate typical soil incorporation rates for manure from treated sheep to range from 0.16 ppb to 5.1 ppb. (From http://www.fda.gov/c...31-392FONSI.pdf ) Therefore, it?s possible for collies and other breeds known to have the mdr1 mutation to consume a toxic dose of ivermectin from eating the manure of recently wormed stock. The timing of worming stock with avermectins should also be taken into account when giving farm dogs heartworm preventative to prevent accidental overdose.

Partial list of drugs known or suspected to cause problems in dogs with the mdr-1 mutation

Ivermectin (antiparasitic agent)
Loperamide (Imodium?; over-the-counter antidiarrheal agent)
Doxorubicin (anticancer agent)
Vincristine (anticancer agent)
Vinblastine (anticancer agent)
Cyclosporin A (immunosuppressive agent)
Digoxin (heart drug)
Acepromazine (tranquilizer)
Butorphanol (pain control)

Partial list of drugs thought to have the potential to cause problems with the mdr-1 mutation

Ondansetron
Domperidone
Paclitaxel
Mitoxantrone
Etoposide
Rifampicin
Quinidine
Morphine

Reference: Neff, et al, 2004


As far as the internet reports on cases of ivermectin sensitivity in border collies, as I said, I contacted the people who do the gene test and they said no border collies had been confirmed to have the mutation. I asked specifically about the unconfirmed reports and they are still unconfirmed. The number of border collies that've had the test is now over 300.

Christine, it's very difficult to get the appropriate dose of ivermectin from the injectable and you can't use water to make it more dilute. The dose he told you is way too much anyway. A safe dose of ivermectin can easily be measured with a small syringe from Ivermectin sheep drench (0.08% Ivermectin) at somewhere around 1/2 ml per 40lb dog.
Denise Wall
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#20 Denise Wall

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Posted 15 August 2005 - 08:49 AM

Laura wrote:

I noticed on the website Denise linked to that the ingredient in Imodium has been reported to cause problems in dogs with the MDR1 gene. I'm curious if this means that a dog who has a reaction to Imodium should be tested for ivermectin sensitivity? And if a dog does not have a reaction to Imodium, does that automatically mean they do not have an ivermectin sensitivity?

I don't know the answer to this question. There are all kinds of drug reactions that can occur that might have nothing to do with the mdr1 gene so I wouldn't use an Imodium reaction as an absolute indicator. However, if it were my dog, I'd probably have it tested for the mutant mdr1 gene since, as I noted above, there are a number of drugs involved, not just the avermectins.
Denise Wall
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