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Heartgard Heartworm meds dangerous???

Joe Anne

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I just got a phone call from my daughter who was talking to her new vet about heartworm meds for her BC puppy. Her Vet said she never gives Heartgard to Collies (any collies!). She said that the Heartgard contains, Ivermectin, and can cause sever illness and sometimes psychosis in Collies. She said she always gives Interceptor for all Collie dogs.

Does anyone know of this or have experience with either medication???

I did get the info to search out the meds.. go to google and type in, Ivermectin Collies, and there is supposed to be lots of info.

JoeAnne Mirra,Sitka, Phoenix and crew

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Thanks Eileen... I did go to all the previous posts, and also searched on google. The info is overwhelming, but I think I've read enough to ask my vet to switch us to Interceptor. I figure at the very least, with Interceptor you have to have twice the dose/amount to become toxic. That's better, but not great.

I hate giving my dogs any of this stuff, but I had 2 dogs years ago(1976), get heart worms, before heartworm meds were recommended by vets. Luckily we discovered them during a complete physical needed to move across country to California, pure luck!

They received treatment, with arsenic (sp) IV for 7 days! It was hit and miss, too much..kills dog, not enough...dose not kill heartworm larvae. Thank God, both my boys lived to a ripe old age of 14 & 15 yrs. old. I don't ever want any of my babies to go through that again.

Thanks for pointing me in the right direction.

JoeAnne Mirra,Sitka,Phoenix and crew

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Joe Anne,


this is the information you're looking for. It's interesting that in both cases (Interceptor and Heargard) the breed that is most sensitive is rough-coated collies. I wonder why no one ever mentions that collies are sensitive to interceptor?




Interceptor (milbemycin oxime) dose: 0.23 mg/lb body weight


A rising-dose safety study conducted in roughcoated collies manifested a clinical reaction consisting of ataxia, pyrexia and periodic recumbency in one of fourteen dogs treated with milbemycin oxime at 12.5 mg/kg (25X monthly use rate). Prior to receiving the 12.5 mg/kg dose (25X monthly use rate) on day 56 of the study, all animals had undergone an exaggerated dosing regimen consisting of 2.5 mg/kg milbemycin oxime (5X monthly use rate) on day 0, followed by 5.0 mg/kg (10X monthly use rate) on day 14 and 10.0 mg/kg (20X monthly use rate) on day 32. No adverse reactions were observed in any of the collies treated with this regimen up through the 10.0 mg/kg (20X monthly use rate) dose.


Source: Product label



Heartgard (ivermectin) dose: 2.72 mcg/lb body weight (mcg = microgram)


Studies with ivermectin indicate that certain dogs of the Collie breed are more sensitive to the effects of ivermectin administered at elevated dose levels (more than 16 times the target use level) than dogs of other breeds. At elevated doses, sensitive dogs showed adverse reactions which included mydriasis, depression, ataxia, tremors, drooling,

paresis, recumbency, excitability, stupor, coma and death. HEARTGARD? demonstrated no signs of toxicity at 10 times the recommended dose (60 mcg/kg) in sensitive Collies. Results of these trials support the safety of HEARTGARD? products in dogs, including Collies, when used as recommended.


Source: Product label

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Chemical group: Macrocyclic lactone


Trade name: Revolution


Mode of action: Binds to glutamate gated chloride channels in the parasites? nervous system, causing them to open.


Pharmacokinetics: Absorbed through the skin and distributed via the blood. Concentrates in sebaceous glands. Active concentrations are found in the plasma for at least 30 days. Most excreted unmetabolized in the feces, and a small amount in the urine.


Dose: 6 mg/kg (topical) Use in animals over 6 weeks of age.




Dogs: 60 mg/kg (10 X dose) produced no adverse reactions when give to puppies (initially 6 wks old) for 7 monthly treatments. 18 mg/kg (3 X dose) produced no effect on reproduction in females or males and no problems in heartworm positive dogs (but it did reduce the levels of microfilaria to nil by the 3rd monthly treatment). 3 monthly doses of 30 mg/kg (5 X dose) produced no adverse effects in avermectin sensitive collies. (See: Novotny, MJ, et al. 2000. Safety of Selamectin in Dogs. Vet. Parasitol. 91:377-391).



Source: http://cal.vet.upenn.edu/dxendopar/drug%20.../selamectin.htm

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