# Accidental Ivermectin Overdose on Weanling



## anndankev (Aug 9, 2010)

It is good you called the vet. Hope he turns out ok.

My sister lost a colt to an impaction of large strongyles the night after his first worming. And he was given less than the recommended dose.


Good Luck.


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## Foxhunter (Feb 5, 2012)

I too have had the same thing happen, nothing bad happened.


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## SilverMaple (Jun 24, 2017)

The only one you really have to worry about overdose if this happens with is Moxidectin. Most of the other equine dewormers have a very large safety margin.


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## anndankev (Aug 9, 2010)

Smilie said:


> ... I would worry about parasite control, period, if I had a foal that carried such a heavy burden of ascarids!


Yes, you and all are correct. (Or should I say all y'all?) LOL 

What was given was feed through Strongid C.
The colt was kept on someone else's property.
My sister had expressed concern that he was wormy, and asked the people several times to worm him. The people were cattle farmers. They did not ever worm him.
At about 6 mo old he was sent to a trainer for basic handling introduction...
It happened the first night the colt was there.

I did not know that Ivermectin and other wormers had a large safety margin. It's good to know that. But I certainly will not use the feed through one that was used.


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## jaydee (May 10, 2012)

Moxidectin is the one that you need to worry about where correct dose is concerned - even more so if you use the combined wormer that also contains praziquantel


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## Smilie (Oct 4, 2010)

Far as the daily feed through de =wormer, it can be a real problem,, in the fact, if that horse is never given some exposure to parasites, then the horse never develops any resistance.
Most older horses in good health, develop some resistance to ascarids (round worms), and why they are just of major concern in foals.

However, horses that have always been fed daily feed through dewormers, wind up somewhere that the practice is not followed, have been known to develop a serious ascarid infections, as their system is as naive as that of a foal.

Of course rescue horses that are in poor condition, also often have high ascarid worm burdens, because their run down condition does not allow for a good immune response, plus exposure , plus lack of de worming, also sets them up for a heavy worm burden, that can cause impaction, mainly due to ascarids, , due to their size,when their is a large worm die off, upon de worming.

That is also why in those scenarios, is the only time it is recommended to under dose with a de =wormer. Not due to the de wormer itself, but the large sudden die off of ascarids, which can, due to their size, relative to other worms, cause an impaction

Yes, because of the narrow safely margin of Moxidexin, that de wormer is recommended not to be used in foals. Excess is stored in fat, and foals have very little fat reserve.


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## Smilie (Oct 4, 2010)

For interest sake only, if anyone wishes to know, the following paragraph explains the wide dose safety margin of Ivermectin. That vet should have known this fact!

'Mode Of Action
Ivermectin is a member of the macrocyclic lactone class of endectocides which have a unique mode of action. Compounds of the class bind selectively and with high affinity to glutamate-gated chloride ion channels which occur in invertebrate nerve and muscle cells. This leads to an increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the nerve or muscle cell, resulting in paralysis and death of the parasite. Compounds of this class may also interact with other ligand-gated chloride channels, such as those gated by the neurotransmitter gamma-aminobutyric acid (GABA).

The margin of safety for compounds of this class is attributable to the fact that mammals do not have glutamate-gated chloride channels, the macrocyclic lactones have a low affinity for other mammalian ligand-gated chloride channels and they do not readily cross the blood-brain barrier.


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## Smilie (Oct 4, 2010)

This is what a study showed, far as moxidexin and toxicity in foals

'Conclusion: One to two week old foals given either the recommended dose level of moxidectin 2% Equine Oral Gel for three consecutive days or a single 3X treatment showed no clinical signs of toxicity. Foals treated with 3X levels on multiple occasions and a single 5X treatment exhibited clinical signs indicative of toxicity which included depression and incoordination, abnormal head carriage, droopy lips and ears, protruding tongue, vacant eye stare, tremors, recumbency and inability to nurse. These signs were reversible with time and supportive nutrient therapy.

If I re -call, from an equine seminar that I Attended, the outer limit of dose safety in older horses, far as moxidectin is 4 times the normal dose, while Ivermectin is around 40 times
Just to be sure I never used quest in any horse under one year of age


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