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WORM OF THE MONTH
We're continuing our series of 'Worm of the Month' articles about deworming medications.
This month: Moxidectin
Moxidectin is a 'macrocyclic lactone' and one of three such dewormers for the equine market, along with ivermectin and albamectin. While not effective against flukes or tapeworms, moxidectin is effective against cyathostomes, or small strongyles, as well as other parasites such as bots. Overdosing is a real concern with moxidectin, especially when deworming foals or debilitated horses, and care should be taken in these circumstances.
Marketed under the name Quest by the Fort Dodge Animal Health company, moxidectin was introduced in 1997. It works by interfering with neurotransmission, paralyzing muscles in the parasite's body walls and in the pharynx, which pumps food into its intestine.
Moxidectin can be used to address encysted small strongyles in the equine large intestine; with the proper dosage it will work in a single dose, similar to the five-day double dose fenbendazole protocol but without the higher cost or the concern about parasite resistance that fenbendazole brings.
However, there can be concerns about safety, and the potential exists for overdosages and adverse reactions.
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Moxidectin is widely used to target
encysted small strongyles and other parasites,
but care should be taken
in estimating the proper dosage for your horse.
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While the product's contraindication details indicate that Quest is safe for horses and ponies, breeding stock, and foals over the age of six months, additional product summary details at horse.com (the Web site for Country Supply) say that care should be exercised when giving it to ponies, miniature horses, and foals.
There are several reasons for this concern. One is that the overdose tolerance threshold is much lower with moxidectin than with some other dewormers, and dosing based on inaccurate weight estimates, or a slip of the oral syringe, can lead to too much in the horse's system.
The other factor is that moxidectin can become highly concentrated in horses with little body fat, allowing it to cross the blood-brain barrier, which it normally doesn't do in mammals. Clinical signs of moxidectin toxicity can include weakness, depression, seizures, and even coma; watching dewormed horses closely for the first 24 to 48 hours after deworming can be a good practice.
Additionally, debilitated horses, or those with a suspected heavy parasite infestation, should be dewormed several times with a less effective dewormer prior to using moxidectin, to reduce the possibility of massive parasite die-off and any resulting issues.
Horse owners who are interested in using moxidectin should read A Review of the Use of Moxidectin in Horses; this 6-page tutorial article by J. Schumacher and J. Taintor goes into great detail about moxidectin and its application, with enough research citations to satisfy even the most inquisitive minds, yet contains useful information on topics such as efficacy, toxicity, and control of various parasites using moxidectin.
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If you want to read up on specific parasites or dewormers we've covered, check our Archive for past Worm of the Month articles.
If we can be of help, please email us at hlab@horsemenslab.com or call us at 800-544-0599.
Return to the November issue of Worm Control News
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Worm Control News is written and produced by KempEquine.com
Copyright 2010 Horsemen's Laboratory. Please contact us at hlab@horsemenslab.com for reprint permission. Linking to Worm Control News is acceptable, and we would appreciate notification of links so we can acknowledge them in future issues.
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