Milbemycin A4 oxime

Topical amitraz is the only approved treatment for CGD; however, it is not always effective or well tolerated. Extra-label use of amitraz, milbemycin oxime, ivermectin, and moxidectin may be effective therapeutical alternatives for dogs with resistant CGD or dogs that have an intolerance to the licensed amitraz protocol. It appears that oral administration of milbemycin oxime (1-2 mg/kg), ivermectin (400-600 micrograms/kg), and moxidectin (400 micrograms/kg) daily is a practical therapeutical alternative and would provide similar cure rates. Nevertheless, milbemycin oxime is expensive, ivermectin is potentially more toxic, and only limited information is available on moxidectin. The average treatment duration with these new regimens is 4 months, with an expected range of 3 to 10 months. Treatment should be administered daily for a minimum of 3 months and for at least 1 month after a series of negative skin scrapings. For chronic cases or cases that take a relatively long time to respond to therapy, 2 to 3 months of treatment beyond negative scrapings may be more appropriate. Dogs with CGD always approach clinical normalcy weeks to months before negative skin scrapings are obtained. All dogs respond at their own rate; as long as the skin scrapings at each visit show fewer mites, the current therapy should be continued for an additional month. If the mite count starts to increase, this may suggest that the treatment protocol is not being followed or it may be that the therapy chosen was suboptimally effective. Although CGD is still a disease that is not easily treated, the prognosis for dogs with this disorder has dramatically improved in the past few years. It must be remembered, however, that the treatment alternatives for CGD described above are not approved and should not be used unless the approved therapeutical regimen has failed.

Background and objectives:These guidelines were written by an international group of specialists with the aim to provide veterinarians with current recommendations for the diagnosis and treatment of canine demodicosis.Methods:Published studies of the various treatment options were reviewed and summarized. Where evidence in form of published studies was not available, expert consensus formed the base of the recommendations.Results:Demodicosis can usually be diagnosed by deep skin scrapings or trichograms; in rare cases a skin biopsy may be needed for diagnosis. Immune suppression due to endoparasitism or malnutrition in young dogs and endocrine diseases, neoplasia and chemotherapy in older dogs are considered predisposing factors and should be diagnosed and treated to optimize the therapeutic outcome. Dogs with disease severity requiring parasiticidal therapy should not be bred. Secondary bacterial skin infections frequently complicate the disease and require topical and/or systemic antimicrobial therapy. There is good evidence for the efficacy of weekly amitraz rinses and daily oral macrocyclic lactones such as milbemycin oxime, ivermectin and moxidectin for the treatment of canine demodicosis. Weekly application of topical moxidectin can be useful in dogs with milder forms of the disease. There is some evidence for the efficacy of weekly or twice weekly subcutaneous or oral doramectin. Systemic macrocyclic lactones may cause neurological adverse effects in sensitive dogs, thus a gradual increase to the final therapeutic dose may be prudent (particularly in herding breeds). Treatment should be monitored with monthly skin scrapings and extended beyond clinical and microscopic cure to minimize recurrences.

Macrocyclic lactones (MLs) have many anti-parasitic applications in small companion animal medicine. They were first developed as chemoprophylactics against heartworm (Dirofilaria immitis) infection to be applied monthly for retroactive killing of third- and fourth-stage larvae. ML-containing products formulated for oral (ivermectin, milbemycin oxime), topical (selamectin, moxidectin) or injectable sustained release (moxidectin, ivermectin) are approved for heartworm prevention in dogs or cats. Clearance of microfilariae and gradual or "soft" killing of adult heartworms constitute increasingly prevalent extra-label uses of MLs against D. immitis. Some commercial ML formulations contain sufficient levels of active ingredient (milbemycin oxime, selamectin, moxidectin) to support additional label claims against gastrointestinal nematode parasites such as hookworms (Ancylostoma spp.) and ascarid round worms (Toxocara spp. and Toxascaris leonina). Beyond these approved applications, safe, extra-label uses of MLs against nematodes parasitizing the urinary tract, such as Capillaria spp., and parasites of the tissues, such as Dipetalonema reconditum, Dirofilaria repens, Thelazia spp. and Spirocerca lupi, in dogs and cats as well as exotic pets have been reported. MLs as a group have intrinsic insecticidal and acaricidal activity, and topical or otic formulations of certain compounds (selamectin, moxidectin, milbemycin oxime or ivermectin) are approved for treatment and control of fleas, certain ixodid ticks, sarcoptiform and demodectic mange mites and psoroptiform ear mites. Extra-label applications of MLs against ectoparasites include notoedric mange mites, dermanyssids such as Ornythonussus bacoti, numerous species of fur mite (e.g. Cheyletiella spp. and Lynxacarus) and trombiculids ("chiggers") in cats, dogs and nontraditional or exotic pets.

Many strains of zygomycetes and actinomycetes were found to convert milbemycin A4 (1a) to 13 beta-hydroxymilbemycin A4 (1b). Among these strains, Cunninghamella echinulata ATCC 9244 had the most efficient 13 beta-hydroxylation ability on milbemycins. In the conversion of milbemycin A3 (2a), 29-hydroxymilbemycin A4 (4a), and 30-hydroxymilbemycin A4 (5a) with this strain, only 13 beta-hydroxylated products were obtained. On the other hand, starting from milbemycin A4 (1a) and 5-ketomilbemycin A4 5-oxime (6a), 13 beta,24- and 13 beta,30-dihydroxy derivatives were also isolated along with 13 beta-hydroxylated products. Similarly, conversion of milbemycin D (3a) and LL-F28249 alpha (8a) gave 13 beta- and 28-hydroxy derivatives (8b and 8c).