Treatment of Demodicosis mange in Australia journal article

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Treatment of Demodicosis mange in Australia journal article

Postby malernee » Fri Aug 19, 2005 7:53 am

Treatment of Demodicosis – What are the facts?
Recently I have had several queries about treatment options for
demodicosis. Most of these seemed to occur after the visit of a drug rep
promoting a new product.
There are several accepted effective therapies for demodicosis including
Amitraz (Demadex®), Ivermectin (Avomec®) and Milbemycin oxime
(Interceptor®) but comparison of their relative efficacies is
difficult due to studies being conducted under different conditions and
with varied drug doses. One of the major problems with efficacy studies
is the selection of animals for a treatment. In cases of juvenile onset
demodicosis 90% of localised cases and 30-50% of generalised cases will
self cure, without specific treatment in 6-8 weeks. If these are
included in a study high success rates could be achieved with a placebo.
All treatments of these treatments have similar success rates over 90%
for cure but relapses often occur.
In practice the majority of failures when using these drugs relates to
compliance and monitoring issues. The problem usually results from the
fact that clinical cure usually occurs weeks to months before
parasitological cure.
The only licensed product in Australia is amitraz applied weekly as a
250-500 ppm rinse. Unfortunately this is not 100% effective at
eliminating demodex infestations. In North America it is licensed for
fortnightly use at 250 ppm and if used correctly cure rates of 90% are
to be expected. In some studies concentrations of 500 or even 1000 ppm
have been used with increasing effectiveness. If used weekly under the
Australia licensed protocol a higher success rate should be expected.
Even in cases of complete parasitological cure up to 25% of generalised
demodecosis recur within 1 year. Unfortunately amitraz is unpleasant and
labour intensive to use. Owners also need to be warned that they may
have untoward effects if they are not careful to avoid contact with the
solution. These include contact dermatitis, migraine headaches and
asthma attacks. Dogs are often sedated through the action of amitraz on
alpha adrenergic receptors particularly if the skin is damaged but this
can be reversed by using atipamezole (Antisedan®).
Ivermectin is the most popular unlicensed product for treatment of
demodicosis with numerous references for its use. Cure rates quoted for
generalised demodicosis are comparable to amitraz. It is relatively
cheap and easy to use. Unfortunately there is the potential for fatal
idiosyncratic reactions to occur with its use.
Ivermectin is a macrocyclic lactone acting on parasite GABA receptors.
To minimize the risk of fatal side effects when using ivermectin a
protocol has been established where the dose is titrated upwards from 50
to either 300 or 600 ug/kg while carefully monitoring for signs of
toxicity. The dose is then continued daily until cure.
The third standard treatment is milbemycin oxime (Interceptor®)
2mg/kg/day. This has similar cure rates to amitraz. Unfortunately this
is a very expensive option unless special deals can be made with the
manufacturer to get discounted stock.
The new product being promoted is doramectin (Dectomax®) a macrocyclic
lactone having a more prolonged action than Ivermectin. It has been used
to treat demodicosis at 600ug/kg weekly. Unfortunately limited studies
on its use have been published; I have only found one study performed in
India and an anecdotal report in the PGFVS control and therapy to
support its use. I am not in the position to make specific comments
about the study performed by the University of Queensland as it is yet
to be published. There is as yet no evidence of improved success using
doramectin compared to other macrocyclic lactones. As there is little
published literature on doramectin I would only use it as an alternative
to ivermectin if I felt the need to maintain complete control of the
situation by administering all medications. I would also have to
consider the risks associated with using a longer acting product on
My personal approach is to offer the licensed product amitraz and
discuss ivermectin as a well established alternative therapy stressing
the potential risks and techniques for avoiding them. Then allow the
owner to decide which therapeutic option suits them. If these treatments
are ineffective or not suitable then the use of doramectin or milbemycin
may be justified.
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