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How effective are isoxazolines for treating canine demodicosis?

11 July 2019, at 9:00am

Could a combination of imidacloprid and moxidectin be a better option for treating red mange?

Around three years ago, canine demodicosis, or red mange, was found to be treatable by a new class of drugs: isoxazolines. Now, a new Knowledge Summary in Veterinary Evidence has compared its efficacy against that of the commonly prescribed combination of imidacloprid and moxidectin.

Under the skin of canine demodicosis

In dogs, demodicosis is caused by an overabundance of Demodex canis, a species of the Demodex genus of mites that lives in the hair follicles. The mites naturally occur in low numbers and don’t pose a problem unless they reproduce in larger amounts. When this happens, it is assumed to have been triggered by immunosuppression or a genetic defect in the immune system of the skin.

Clinical signs can be local or generalised and range from small patches of mild skin irritation and hair loss, to severe body-wide inflammation and even purulent discharge when accompanied by a bacterial infection.

There are a number of treatment options for demodicosis in dogs, but best practice is still an area of discussion. This is confounded by a number of factors, such as the licensing of particular drugs depending on country; inconsistent dos-age and administration; poor owner compliance; potentially serious side effects; misdiagnosis of the condition; underlying or secondary medical problems; and the difference in presentation of the disease in adults and juveniles.

Comparative efficacy of isoxazolines

The Knowledge Summary “Choosing treatment for dogs with generalised demodicosis – isoxazolines or imidacloprid and moxidectin?” aimed to investigate the evidence for two of the most promising treatment options.

By appraising five relevant studies, the Knowledge Summary concluded that isoxazolines have comparable efficacy to a combination of imidacloprid and moxidectin.

Three different and widely available forms of isoxazoline were tested among the studies – sarolaner, fluralaner and afoxolaner, given either orally or topically.

Across the studies, treatment success – as measured by gold standard mite counts on skin scrapings – was broadly similar, although isoxazoline groups achieved a marginally better reduction in mite counts. The differences, however, were not significant and could be explained by dosage frequencies or severity of disease.

Treatment with imidacloprid and moxidectin, on the other hand, tended to require more frequent dosage (ie once per week rather than monthly) and this may be a consideration for the veterinary professional, especially if treatment is reliant on successful owner compliance with administration at home.

All of the available studies were sponsored, and in most cases authored, by the pharmaceutical companies that prepare the isoxazoline. As a result, bias in study design, especially considering the nuances of treating individual presentations of the disease, is possible. However, the evidence is strong enough to support the use of isoxazolines for treating canine demodicosis.

Cautions for the veterinary professional

In 2018, the US Food and Drug Administration released a fact sheet (“Fact sheet for pet owners and veterinarians about potential adverse events associated with isoxazoline flea and tick products”) on the topic of side effects.

Although uncommon (none were noted in the studies appraised by the Knowledge Summary), drugs in the class have been associated with significant neurological side effects, including muscle tremors, ataxia and seizures, in dogs and cats. Veterinary surgeons should be particularly cautious about prescribing any such drug to animals with a prior history of neurological conditions or reactions.

Isoxazolines are not yet licensed for use in all countries, so the prescribing vet is urged to check local regulatory body advice. Similarly, they are advised to examine drug guidelines for dosage suggestions – this goes for all treatment options including imidacloprid and moxidectin, which is recommended as a monthly administration unless the case is severe.

The full Knowledge Summary can be read here.