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Radiolabeled amitraz was administered to beagles as a single oral treatment at a level of 4 mg/kg. Peak blood levels were reached between 1.5 and 6 hours posttreatment; the half-life was approximately 12 hours during the initial 48 hours. Radioactivity was extremely low in whole blood and plasma at 72 (0.05-0.06 ppm) and 96 (0.03-0.06 ppm) hours. The organs having residues at levels greater than plasma concentrations at 96 hours included: liver, skin, eyes, bile, kidney, medulla, cerebrum, lungs, gonads, fat, thyroid, spleen, and large intestine. The main metabolite isolated from these tissues was identified as 4-amino-3-methylbenzoic acid, which is nontoxic for the dog.
Studies have not been conducted to quantitatively determine absorption by the dog following topical or dermal treatment with amitraz. The technical drug (amitraz) and formulated material (MITABAN Liquid Concentrate) have been extensively evaluated in laboratory and domesticated animals in a series of acute, subchronic and chronic studies.
The mechanism of action for amitraz is unknown, however data currently available suggest the drug may act on the central nervous system. In vitro housefly tests indicated amitraz does not have significant cholinesterase inhibitory activity.
The most frequently observed adverse reaction in the clinical studies was transient sedation, which occurred in approximately 8% of the generalized demodicosis patients. This effect was observed within 2 to 6 hours posttreatment, and usually dissipated within 24 to 72 hours. In approximately 40% of the affected generalized demodicosis patients, the effect dissipated in less than 24 hours. Sedation often was less apparent when additional MITABAN (amitraz) treatments were applied, however in approximately 35% of the generalized demodicosis patients sleepiness was observed after each treatment. Transient pruritus, which clinical investigators considered to be an indirect effect due to an inflammatory reaction associated with dead mites, occurred in less than 3% of the generalized demodicosis patients. This effect usually occurred and dissipated within 24-48 hours posttreatment. Other observations noted by the clinical investigators and/or clients were a low incidence (less than 1%) of convulsions, ataxia, hyperexcitability, personality change, hypothermia, appetite stimulation, bloat, polyuria, vomition, diarrhea, anorexia, edema, erythema and other varying degrees of skin irritation. Three fatalities were recorded.
Dermal or ocular responses were not observed when MITABAN was applied at recommended or exaggerated concentrations to the skin and incidentally to the eyes of dogs (in controlled experiments simulating recommended use). However, such responses have been infrequently reported from clinical use. (See PRECAUTIONS).
Amitraz was orally administered to nondiseased beagles at levels of 0, 0.25, 1 and 4 mg/kg once daily for 90 days. There were no deaths in any of the groups. At 3 hours posttreatment and for only the initial three days of the 90 day experiment, dogs treated with 4 mg/kg exhibited CNS depression and ataxia; the effects remained for 3 to 6 hours and the dogs were normal within 24 hours posttreatment. Vomition occurred in two dogs on only the initial two days of the study. Thereafter (days 4 through 90) the dogs appeared to be subdued for approximately 6 hours after dosing, and ataxia was nearly impossible to detect. In the initial 48 to 72 hours, dogs treated with 1 mg/kg/day exhibited signs of depression (without ataxia) for 4-6 hours; subsequently the depression became less marked and of shorter duration. At 3 hours after dosing, dogs treated with 1 or 4 mg/kg consistently had subnormal rectal temperatures and pulse rates; both parameters returned to normal within 24 hours posttreatment. At 0.25 mg/kg/day, the dogs appeared normal throughout the experiment. Hyperglycemia consistently occurred in dogs treated with 1 and 4 mg/kg/day and rarely occurred in dogs at the 0.25 mg/kg level; this response was maximal within 6 hours posttreatment and serum glucose values returned to normal within 24 hours after treatment. Grossly there was a significant increase in liver weights for dogs treated at the 4 mg/kg level, however microscopically the findings were minimal and consisted of a slight enlargement of the central and midzonal hepatocytes; the degree of enlargement was not dose related. However, at the two higher doses the area affected appeared more prominent as reflected by an increase of the periportal hepatocytes. In the adrenal gland, several dogs treated with the two higher levels had thinning of the zonae fasiculata and reticularis, which may be associated with slight hyperplasia of the zona glomerulosa.
Three to six topical treatments (14 days apart) are recommended for treatment of generalized demodicosis. It is important to continue the treatment until no viable (alive) mites are found in the skin scrapings at two successive treatments, or until six treatments have been applied. Severe (chronic) cases and dogs which are reinfested may require a second and third series of treatments, and again the treatment should be applied at 14 day intervals. Discontinue treatment of dogs which do not respond clinically.
When employing MITABAN for treatment of demodicosis, other dogs in the home also should be examined for lesions to ascertain whether treatment of these animals is warranted.
The efficacy of MITABAN (amitraz) was extensively evaluated on dogs experimentally or naturally parasitized with Demodex canis. Three to six MITABAN treatments (250 ppm active drug), at 14 day intervals, were highly efficacious for treatment of naturally acquired demodicosis. MITABAN treatment was continued until all Demodex in the skin scrapings were dead or the dogs no longer harbored mites at two successive treatments, or the animal received six treatments. Ninety-six percent of the dogs were cleared of mites.
Eighty percent of the generalized demodicosis patients were returned to clinical normalcy and did not require additional therapy after receiving one treatment series. Twenty percent of all patients with generalized demodicosis required a second treatment series. When retreated, the 14 day treatment interval was again followed, and these patients received an average of 5 treatments. Greater than 90% of the dogs clinically improved, and the average clinical response of these patients was approximately 80%. Greater than 96% of all generalized demodicosis patients returned to normalcy after receiving one or two treatment series and did not require further therapy. Between 3 and 4% of all generalized demodicosis patients were returned to the investigators and required therapy beyond the second treatment series; these patients received a third or fourth series of MITABAN treatments. Greater than 99% of all generalized demodicosis patients returned to normalcy after receiving one, two, or three treatment series, and did not require further therapy; less than 1% of the patients required additional therapy.
Store at controlled room temperature 20° to 25°C (68° to 77°F) [see USP].
Caution: Federal (USA) law restricts this drug to use by or on the order of a licensed veterinarian.