Veterinary Medicine - August 2008 - (Page 455)

binds to glutamate-gated and gammaaminobutyric acid (GABA)-gated chloride channels in the mite’s nervous system, resulting in cell hyperpolarization, mite paralysis, and, nally, death. Macrocyclic lactones do not readily cross the mature mammalian blood-brain barrier.17 Safety in mammals is due to the lack of glutamate-gated chloride channels in the peripheral nervous system and the restriction of GABA to the central nervous system. The ease of oral administration compared with dips makes macrocyclic lactones the rst line of therapy for many dermatologists (Table 5). Unfortunately, the use of macrocyclic lactones for generalized demodicosis is considered extralabel, and there is no antidote to the potentially serious and life-threatening side effects. Also, dogs should have negative heartworm disease test results before macrocyclic lactone therapy is implemented. When using macrocyclic lactones for generalized demodicosis, the owner must understand its extralabel use and potential for side effects. Some dermatologists will have the owner sign a consent-to-treat form outlining this information before macrocyclic lactones use. TABLE 4 Protocol to Maximize Amitraz Dip Efﬁcacy in Dogs • When a deep pyoderma with draining tracts is present, treat the infection with a beta-lactamase-stable antibiotic selected from bacterial culture and antimicrobial sensitivity testing before starting the amitraz dips. • Clip medium- and long-haired dogs to improve contact between amitraz and the skin. • Remove crusts whenever possible. • Bathe the dog with an antibacterial shampoo before dipping to help remove surface debris (can be done the day before). • Read the amitraz product label and precautions. Mix a new batch of dip at the time of dipping. • Personnel applying the dip should wear protective clothing and gloves. Handlers taking MAOIs or with respiratory disease or diabetes should not administer amitraz. Dip in a well-ventilated area. • Apply amitraz by wetting and sponging the entire body every seven to 14 days. Allow the dog to stand in the run-off solution so that its paws are treated. Avoid the eyes and mucous membranes. An Elizabethan collar may be needed to prevent the dog from licking and ingesting amitraz. Allow the dog to air-dry before sending it home. • Do not allow the dog to get wet between dips. • Continue the dips after obtaining two consecutive negative results on skin scrapings (all areas sampled and all mite life stages) taken two to four weeks apart. • For small dogs or patients experiencing mild adverse effects, consider a reduced concentration or dip alternating halves of the body. • An alpha2-adrenergic antagonist can be given when toxicosis is seen or before dipping in patients consistently experiencing toxicosis. Changing miticidal therapy to a macrocyclic lactone is advised in patients adversely affected by amitraz. • Concurrent use of amitraz dips and macrocyclic lactones is strongly discouraged and should be avoided. Ivermectin—For generalized demodicosis, the injectable form of ivermectin is given orally at a dose of 300 to 600 µg/kg/day.10,12 The aqueous formulations may be more palatable than are the propylene glycol-based products. Adverse events are sporadic and include lethargy, edematous wheals, mydriasis, muscle tremors, and ataxia. The main concern is the development of signs attributable to severe neurotoxicosis including depression, stupor, coma, ataxia, and seizures; death can also result. Blindness has also been reported in dogs.18 To better identify ivermectin-sensitive dogs, one report recommends initially Download a consent form for extralabel ivermectin usage at veterinarymedicine.dvm360 .com/Consent. TABLE 5 Macrocyclic Lactone Dosages for Generalized Demodicosis in Dogs Drug Ivermectin* Milbemycin oxime Moxidectin* Doramectin* *Not for use in ivermectin-sensitive breeds. Dosage 300–600 µg/kg PO once a day 1.5–2 mg/kg PO once a day 400 µg/kg PO once a day 600 µg/kg SC every seven days VETERINARY MEDICINE August 2008 455 http://veterinarymedicine.dvm360.com/Consent http://veterinarymedicine.dvm360.com/Consent

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Veterinary Medicine - August 2008 Contents Editors' Note Leading Off ClinQuiz Idea Exchange Practical Matters Diagnosing and Treating Canine Copper-Associated Hepatopathies Canine and Feline Demodicosis CE Form Advertiser Index Product Preview Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2008

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