ABSTRACT OF THE WEEK

Veterinary dermatology
Volume 26 | Issue 5 (October 2015)

Treatment of canine generalized demodicosis using weekly injections of doramectin: 232 cases in the USA (2002-2012).

Vet Dermatol. October 2015;26(5):345-9, e73.

John H C Hutt¹, I Craig Prior², Michael A Shipstone³

¹ Dermatology for Animals, 263 Appleby Road, Stafford Heights, Queensland, 4053, Australia.; ² Murphy Road Animal Hospital, 4408 Murphy Road, Nashville, TN, 37209, USA.; ³ Dermatology for Animals, 263 Appleby Road, Stafford Heights, Queensland, 4053, Australia.

Abstract

BACKGROUND: Generalized demodicosis is a severe skin disease in the dog, with limited treatment options. HYPOTHESIS/OBJECTIVES: To demonstrate that doramectin, when given at a dose rate of 0.6 mg/kg body weight, is a safe and effective treatment for generalized demodicosis in the dog. ANIMALS: Four hundred client-owned dogs diagnosed with generalized demodicosis at one general small-animal practice. Of these, 232 completed their treatment and were included in the study. METHODS: A retrospective study was carried out by searching the computerised medical records of dogs seen at one general small-animal practice in Tennessee, USA. The records of each dog with a diagnosis of generalized demodicosis, who underwent treatment using weekly injections of doramectin at a dose rate of 0.6 mg/kg body weight, were analysed. RESULTS: Remission was achieved in 94.8% of dogs treated with weekly subcutaneous injections of doramectin at a dose rate of 0.6 mg/kg body weight. Adverse events were rare with two suspected instances (0.5%) being recorded. The mean duration of treatment was 7.1 weeks. CONCLUSIONS AND CLINICAL IMPORTANCE: Doramectin given at a dose rate of 0.6 mg/kg body weight by subcutaneous injection at weekly intervals is a useful and well-tolerated treatment for generalized demodicosis in the dog.

Companion Notes

Retrospective report on the efficacy of weekly doramectin sc injections for generalized demodicosis in 232 dogs

- in past 5 years, authors have received funds and/or support from Zoetis, Novartis

- and Elanco Animal Health

Introduction on canine generalized demodicosis (GD)

- a severe skin disease that can result in death

- there's no consensus on what is localized vs generalized disease

- adult-onset disease may be associated with underlying problems including:

(cause and effect unproven)

- hypothyroidism

- hyperadrenocorticism

- leishmaniasis

- malignant neoplasia

- immunosuppressive treatment

- breeds reported most susceptible to juvenile-onset disease in a large US study

- American Staffordshire terrier

- Staffordshire bull terrier

- Shar Pei

- in 2 non-blinded studies, doramectin 0.6 mg/kg every 7 days was used to treat GD

- in one, doramectin was given sc to 23 dogs

- "appeared to be marginally more effective [than PO use]"

- in a separate study sc use resulted in slower drug absorption than PO use

- also greater bioavailability compared to oral administration

- in other, it was given PO to 29 dogs

Study design

- study population: dogs seen at a private clinic in Nashville, TN, USA from 02-12

- 400 dogs with generalized demodicosis found in search of clinic records

- generalized demodicosis defined as any 1 of the below:

- 3 or more separate lesions

- 2 or more feet affected

- single entire body region affected

- mean age at initial presentation: 11.25 months with a range of 2-164

- 51.1% were under 6 months of age

- 29.5% were 6-12 months of age

- 4.3% were over 4 years old and they underwent further testing:

- CBC, biochemistry, urinalysis and total T4

- 47.1% diagnosed with an underlying or intercurrent disease

- 168 were excluded

- 93 had only 1 negative skin scraping performed

- 43 failed to complete treatment

- lost to followup

- owners declined further treatment despite lesions present

- dog died due to other reasons

- diagnosis of other diseases resulting in stopping treatment

- 32 had scheduled skin scrapings not performed or had dead mites

- breeds with a calculated relative risk over 2 included the following:

- percentage of affected dogs vs percentage of total clinic population

- authors caution risk data is questionable in uncommon breeds

- French bull terrier: 25

- dogues de Bordeaux: 25

- bullnese: 25

- affenpinscher: 16.67

- briard: 8.33

- Presa Canario: 8.33

- English bulldog: 7.5

- pug: 4.55

- chow: 3.13

- whippet: 3.13

- coon hound: 3.13

- Welsh terrier: 2.27

- springer spaniel: 2.03

- accounting for data quality for uncommon breeds, authors conclude:

- overrepresented breeds in the geographical area might include:

- American Staffordshire terrier

- Boston terrier

- boxer

- pug

- mixed breed dogs, 61.6% were mixed breed dogs

- in previous reports mostly purebred dogs affected

- underrepresented breeds in the geographical area might include:

- beagle

- chihuahua

- dachshund

- golden retriever

- Jack Russell terrier

- Maltese terrier

- shih tzu

- Yorkshire terrier

- 232 completed treatment and were included in study

- procedure: records retrospectively reviewed

- doramectin, 0.6 mg/kg sc weekly

(Dectomax; Pfizer Animal Health, New York, NY, USA)

- used because of poor availability of amitraz

- skin scrapings every 2 weeks starting at time of 4^th injection

- repeat scrapings made at site of original lesions and scrapings

- concurrent bacterial pyoderma treated with antibiotics

- no restrictions on concomitant treatments

Results

- remission rate among the 232 dogs

(remission = 2 successive negative skin scrapings)

- 94.8% of dogs achieved remission

- 1.3% relapsed within 1 month of stopping treatment

- these were successfully retreated (remission) a 2^nd time

- 4.3% were treatment failures, (no detectable reduction in live mite numbers)

- mean duration of treatment: 7.1 weeks with a range of 4-20 weeks

- adverse events

- 2 suspected adverse events recorded, 0.5%

- neurological signs of ataxia developed, 1 case

- resolved when treatment was discontinued

- local irritant reaction to injection, 1 case

- owners declined further treatment

"Overall, we conclude that doramectin given at a dose rate of 0.6 mg/kg body weight by subcutaneous injection at weekly intervals is a useful and well tolerated treatment for generalized demodicosis in the dog."

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