Effectiveness of ivermectin in treating mules assessed in study

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A mule named Juancito at work on the Mitre Peninsula, in Tierra del Fuego, Argentina. Photo: Dario u, public domain, via Wikimedia Commons

The world is home to an estimated nine million mules, but little is known about how even the most common veterinary drugs work on these hardy donkey-horse hybrids.

Marilena Bazzano and her fellow researchers, writing in the journal Animals, note that mules and donkeys are often treated as horses from a therapeutic point of view.

“Little research is available for donkeys but even less is known about mules,” they wrote.

However, this therapeutic approach could be dangerous due to species differences, with the different potential action of drugs having an impact on their effectiveness.

For their study, Bazzono and her colleagues explored the use of the common broad-spectrum dewormer ivermectin in mules. This wormer is routinely used off-label in mules, which are a cross between a male donkey and a female horse.

As they point out, improper use of ivermectin, through the likes of the wrong dosage, could cause a lack of parasite control and contribute to the development of drug resistance.

They said studies on the effectiveness of antiparasitic drugs in mules are limited, even though these drugs are crucial to their welfare.

“Significant pharmacokinetic differences might exist between horses and mules, as already observed for donkeys.”

The study team, using 15 adult mules based in Italy, evaluated the effectiveness of ivermectin given orally to mules at the same dosage (200 micrograms per kilogram of body weight) licensed for horses.

All the mules were tested beforehand and had fecal eggs counts of 200 eggs per gram (EPG) or higher, with the exclusive presence of cyathostomins.

Blood was taken from five animals over the ensuing 30 days for analysis, and egg counts were conducted on all the mules two weeks and four weeks after the dose was given. Fecal egg count reductions tests were also performed.

Clinically, none of the animals showed any adverse reaction to the ivermectin dose.

Serum concentrations of ivermectin peaked within the first few hours, then decreased progressively. It was still detectable in all the mules after seven days. In one mule it remained detectable for 10 days, while another still had traces after 15 days and another after 20 days.

Dramatic reductions in egg count numbers were seen at retesting after 14 days and 28 days, indicating the effectiveness of the dewormer.

Results show that giving ivermectin orally, at the same dosage for horses, has what the researchers described as an intermediate pharmacokinetic behavior between that seen in horses and donkeys.

The good news is that the ivermectin oral paste at a horse dosage proved effective and safe for the treatment of cyathostomins, also known as small strongyles, in mules.

They suggested more work might result in a more optimized dose for mules.

Bazzano, M.; Di Salvo, A.; Diaferia, M.; Veronesi, F.; Galarini, R.; Paoletti, F.; Tesei, B.; McLean, A.; Veneziano, V.; Laus, F. Anthelmintic Efficacy and Pharmacokinetics of Ivermectin Paste after Oral Administration in Mules Infected by Cyathostomins. Animals 2020, 10, 934.

The study, published under a Creative Commons License, can be read here

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