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Safety Side-Note: Questions about Big Pharma in the Vet World

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Why I am switching to Ivermectin for Heartworm prevention

All things can be linked to safety.  I am posting this article because it gives great info on how to keep your dogs safe while saving money, and it answers a question that has been bugging me. If that isn’t the point of a blog, I don’t know what is.  Enjoy.

Why I am switching to Ivermectin for heartworm prevention


I just got another dog – his name is Cookie. We are on a budget and Trifexis for heartworm and flea prevention costs A LOT, like $30 a month for 2 dogs. I question everything in the human health world, so why have I been so complacent with what my vet tells me to give my dogs? I started doing some research, and guess what I found out? Big pharmaceuticals or “Big pharma” is everywhere. I feel kinda dumb for not asking these questions sooner! I know that physicians typically prescribe what pharmaceutical companies suggest to them, so why wouldn’t vets do the same thing? I am not judging – I love my vet – she is there when I need her – turns out I just don’t need her to control parasites in my dogs. Hope this is of value to you, and that it confirms – if you want to know the answer to something, ask me (that’s supposed to be funny, ya’ll).


Link to common dog parasites:

According to the American Kennel Club: internal – heartworm; intestinal – hook, ring, round, tape, whipworms and non-worm parasites like coccidian, giardia and spirochetes; external – fleas, ticks, lice, mites.

“The big four” of intestinal parasites: roundworms, tapeworms, hookworms and whipworms (


Heartworms (Dirofilaria immitis) enter through the bite of an infected mosquito, mature in the dog’s heart and clog it. Symptoms include mild, persistent cough, fatigue and reduced appetite – death can result from heart failure. They take 6 months to mature and can live in the dog’s body for seven years and can reach a length of up to a foot. 15 is the average burden. The American Heartworm Society conducts surveys every 3 years ( – includes a map)


For heartworms to be a threat to your dog three things have to happen at the same time: other infested dogs, mosquitoes to carry the parasite, the right temperature.


Treatment is expensive and hard on the dog and must be administered by a veterinarian and in rare cases surgery is needed.


AHS recommends year-round heartworm prophylaxis for maximal effectiveness.


All heartworm preventatives currently marketed belong to the macrocylic lactone (ML) class of drugs: Ivermectin and milbemycin oxime are monthly oral

Moxidectin and selamectin are topically applied monthly, and SR subcutaneous moxidectin can be injected every 6 months

WARNING: Collies and certain other herding breeds have a sensitivity to heartworm preventatives that is genetically based and can be tested for.


Testing: annual and the earliest it can detect infection is about 5-6 months after infection. Antigen testing of stool is the most sensitive, but microfilaria testing is also done in tandem if high suspicion of infection. Juvenile worms can be found as early as 52 days post mosquito bite


Common preventatives:

Heartguard, triheart: ivermectin/pyrantel mixture

Iverhart max: ivermectin/pyrantel mixture + praziquantel

Sentinel: Praziquantel, milbemycin oxime (MO), lufernuron

Revolution: topical selamectin

Advantage: topical imidacloprid + moxidectin

What about Trifexis? Nothing about it on the AKC site or the AHS site:

It contains Spinosad for fleas and ticks and MO for heartworms and intestinal worms – see below.

Milbemycin based heartworm meds like Sentinel and Trifexis cover whips, but most ivermectin based heartworm preventatives do not carry a high enough dose of ivermectin to kill whips

The actual drugs:


Febantel : kills hooks, other ascarids, giardia


Ivermectin (IVM): broad spectrum antiparastic agent: mites, lice, scabies, bedbugs, rosacea, river blindness (onchocerciasis), strongyloidiasis, ascariasis, trichuriasis, filiariasis, enterobiasis. Discovered in 1975, on WHO’s list of essential medicines and the most effective and safe medicines needed in a health system averaging 10cents for a course of treatment.


Doses for heartworm are 50 times lower than for other parasites.


Ivermectin sensitivity will cause dilated pupils or drunken gait progressing to respiratory paralysis and death if medication is not withdrawn. You can try a small dose, observe for side effects and slowly raise dose.


Do not use with spinosad


Study showed 50 mg/kg expelled greater than 99% of adult forms of hooks

100 mg/kg needed for whips (


Article published in AmJVet Res 1996 ( concluded IVM significantly more effective than MBO against heart-worm infection (stage – young adult heartworms)


Lufernuron: insecticide – for fleas and tics


Milbemycin oxime also known as interceptor – broad spectrum antiparasitic effective against worms and mites. Kills fleas and prevents flea infestations, controls adult hookworm, roundworm and adult whipworm.


Prazinquantel (Biltricide) treats parasitic worm infections


Pyrantel (Panacur): treats parasitic worm infections – you can get it at any drugstore for deworming – best for roundworms and hookworms


Selamectin: topical that kills worms and parasites like fleas and ticks


Spinosad: natural substance made by soil bacterium for controlling spider mites, mosquitoes, ants, etc…



A great resource with dosing charts and a chart of each medication and what it kills:


What I am going to do:


I am ordering 8 oz (236 ml) of 0.08% liquid ivermectin for $30, and some 1 ml syringes for dosing.


Using this dosing chart:


0.3 ml monthly for Cookie who weighs 45 lbs

0.4 ml monthly for Z who weighs 60 lbs


This is 8.4 mls per year, so I have enough in that one bottle for 28 years… if only my dogs would live that long.

Bayer quad dewormer requires no prescription and contains all the meds for a good deworming: prazinquantel, pyrantel and febantel) – will get rid of whips, rounds and hooks.


We will continue with the PetArmor plus topical (cheaper than frontline) for dogs and cats to control fleas and ticks – I get the one for GIANT dogs and split it between the two.

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