Medium RiskPet ProductsPillsPoisons in the Home

Iron and Ivermectin – The truth about pet poisons A-Z


Iron and Ivermectin stand in for our letter I. This is one of my favorite letters! It’s one of the few letters that can stand alone as a full word, it’s a pronoun we use to talk about ourselves, and you can dot it with any number of adorable shapes.

While we’ve gone over some pretty nasty poisons with the past letters, our I poisons are among the more common pet exposures!  While both iron and ivermectin can absolutely cause life-threatening signs at certain doses, we usually have time to intervene with the proper care.

Iron and Ivermectin Toxicity in Pets

Small amounts of iron are necessary for life, but too much is toxic!

Vitamin toxicity is something of which many of us are aware due to the warnings about keeping vitamin supplements away from children.  Similar to children, animals have a tendency to ingest large quantities.

Supplements aren’t the only form of iron an animal could access.  There are several products on the market that contain the elemental form, or other Fe salts (usually designated by the word “ferrous”).  The salts are not as concentrated as the elemental form.

A small list of products that contain some form of it includes:

  • Vitamins and supplements
  • Bodybuilding formulas
  • Fertilizers
  • Slug and Snail baits (which often claim to be non-toxic to pets)

The GI tract cannot easily absorb many forms of iron, such as rust. These forms are not harmful if swallowed.  Far more damage is possible with a form of iron that is absorbable, such as iron supplements.


Iron is directly irritating to the stomach/intestines and can cause injury to the tissues.  Doses below 20 milligrams per kilogram only cause mild stomach upset, but amounts above that dose need treatment at a vet clinic. 100 milligrams per kilogram is potentially fatal.

It also causes indirect damage to the circulatory system and the liver.   Thus, exposures tend to come in distinct phases.  The first stage represents the direct damage of the iron upon the stomach. The second stage represents the indirect damage to other body systems. The third stage is related to the vast amounts of scar tissue formed in the stomach and intestines.

Stage One Signs (Up to 6 hours after ingestion):

  • Vomiting (often bloody)
  • Diarrhea (often bloody)

Signs in stage one seem to lessen within 6-24 hours. But after a brief respite, the signs start up again and worsen.  This transitions into stage 2.

Stage Two Signs (6-24 hours):

  • Vomiting
  • Diarrhea
  • GI hemorrhaging
  • Stomach pain
  • Tremors
  • Shock
  • An increase in the acidity of the blood (metabolic acidosis)
  • The inability for the blood to form clots (coagulopathy)
  • Death

If a pet survives stage two signs, they can still have further signs over the course of the following 6 weeks.  The destruction of the tissues in the stomach and intestines causes scar tissues to form.  The inflexible scar tissue can block the GI tract, leading to an obstruction.  This is stage three.

Stage Three signs (up to six weeks after exposure):

  • Vomiting
  • Lack of appetite
  • Inability to hold down water
  • Stomach pain
  • Restlessness
  • Inability to poop
  • Lethargy or weakness
  • Pale gums

If scar tissue develops into an obstruction, a vet will need to perform emergency surgery to clear the GI tract.


An animal that ingests over 20 milligrams per kilogram should go to the vet if it is not safe to induce vomiting at home. A poison control for animals can do the necessary dose calculations.  Different severities of cases require different treatments:

  • Inducing vomiting to remove as much iron as possible.
  • Dry pills and supplements can stick together and form large, dry blockages.  If necessary, these will be removed via surgery.
  • Administration of medications to help soothe the GI tract.
  • Charcoal does not bind to iron, so it is not an appropriate treatment.
  • Supportive care is important for animals experiencing severe signs:
    • IV fluids
    • Stabilization if the patient is in shock
    • Blood work to check organ function
    • Treatment for metabolic acidosis
    • Etc.
  • Administration of a chelator to bond to the iron and remove it from the body.
    • A chelator is a substance that binds to iron and converts it to a form that the kidneys can easily eliminate.

Should the pet survive the initial signs, pet parents will need to watch their pet at home for at least 6 weeks to check for signs of obstruction (stage three).


You’re used to the song and dance of preventing a poisoning by now.  Lock up all pills, and always take them over the sink.  Read your labels thoroughly, and keep anything with iron (or the word ferrous) should be kept out of reach of the family creatures.  While ferrous-based salt snail and slug baits are certainly safer than the alternatives, owners have reported cases of poisoning from large ingestions, so keep the bags locked in a safe place.

Iron and Ivermectin Toxicity in Pets

Commonly used to prevent against heartworms, accidental overdose of ivermectin can be fatal!

Ivermectin is the active ingredient in the majority of heartworm preventatives out on the market.  It’s also widely used in deworming formulas for swine, sheep, cattle, and horses.

The hazards of ivermectin are well-known to the collie/sheepdog owners out there.  Certain breeds have a sensitivity to this substance, but the rest of us often give monthly doses of heartworm prevention without much thought.

Some of us are so comfortable with this common prevention that we don’t hesitate to use horse/cattle dewormers, or cattle ivermectin solution to deworm our house pets.  Unless you are veterinary professional (or given a direct dose by a vet professional), this should NEVER be done.

While the dose of the pre-medicated treats like Heartgard or Iverhart is so small that a pet eating multiple treats rarely has an issue, the livestock formulas are a different story.

Livestock require (and can tolerate) more ivermectin than small animals, partially due to their sheer size.  

Thus the livestock formulas come in different doses and concentrations than the canine/feline pills.  While it may seem an easy thing to just do the math and give a smaller dose, it’s easy to make mistakes in math.  In order to properly convert the dose, you need to be able to:

  • Know how many milligrams per kilogram your pet requires to prevent against heartworms.
  • Calculate the milligram dose based on your pet’s weight.
  • Convert the number of milligrams per milliliter (or grams per milliliter, grams per gram, or milligrams per gram) of the livestock formula in order to dose out the right amount. This is often expressed as a percent, such as a 1% solution.
  • Use the right syringe and get the right amount (The difference between 0.01, 0.1, and 1.0 on the smaller syringes can be extremely difficult to differentiate).

An error in any of those steps could lead to a fatality, and it’s far too easy to misplace a decimal point and end up giving ten times the dose you intended.  Contrary to popular belief, ivermectin is not “perfectly safe”, and overdose can carry some pretty major consequences.


In sensitive breeds (collies, etc), the dose where ivermectin becomes toxic is 0.1 milligram per kilogram.  Non-sensitive breeds can tolerate doses up to 0.2 milligrams per kilogram.

As a comparison, the amount given to a dog for monthly heartworm prevention is roughly 0.0063 milligrams per kilogram.  This means that even a sensitive dog would need to eat about 16 canine heartworm treats to reach the dose of toxicity.

With the higher concentration solutions, a small amount goes a long way.  Signs related to ivermectin toxicity are mostly neurological:

  • Vomiting
  • Dilated pupils
  • Incoordination (ataxia)
  • Heavy drooling
  • Blindness
  • Tremors
  • Seizures
  • Coma
  • Severe decreases in temperature
  • Death

From a product that has been ingested, these signs may develop fairly quickly.  As the injectable form may take longer to absorb, signs may also be delayed.


If your animal has ingested a toxic amount of ivermectin and inducing vomiting isn’t possible at home, vet care is required.  The vet will take several steps to treat:

  • Inducing vomiting (This is only successful within 60 minutes, as ivermectin absorbs fast from the stomach).
  • Activated charcoal in repeated doses.
  • Medication to control any of the above adverse signs.
  • IV lipids have shown some promise in helping it pass through the system.
    • Since ivermectin is fat loving (it combines with and dissolves in fats/lipids), the lipids will bind to the ivermectin and make it pass out easier and faster.


Aside from the usual habit of locking up medications out of your pet’s reach, livestock owners should be particularly careful.  Herding breeds like border collies are common on the farm, and a dog that is present while the horses are being dewormed is in danger of licking up any dribbled deworming paste.  Such a harmless small amount to a horse is devastating to a dog (especially a sensitive one).

Ivermectin isn’t the only thing that horses tolerate better than dogs, so make sure your dogs don’t have access to any medications or supplements in the barn, or discarded paste syringes in the trash can.

Coming up are our J’s!

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