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  • Author or Editor: Walter H. Hsu x
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Amitraz is presently the only FDA-approved treatment for demodicosis in dogs in the United States. Amitraz treatment involves a protracted course of administration and risks of severe adverse effects such as sedation, bradycardia, and respiratory depression, which are caused by activation of α2-adrenergic receptors. Other treatment options include macrocyclic lactones and lime sulfur, but these products have varied efficacy and high risks of adverse effects. Several recent studies have indicated that isoxazolines are capable of reducing Demodex mite counts in canine and feline patients with demodicosis by ≥ 99% in as little as 1 month with few adverse effects. This article reviews the status of isoxazolines in regard to labeled uses in dogs and cats in the United States, extralabel clinical use for treatment of demodicosis in these species, and safety of orally administered formulations of these drugs.

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in Journal of the American Veterinary Medical Association


Three doses of an α2-adrenoreceptor antagonist, atipamezole, were administered to reverse xylazine-induced sedation, bradycardia, and ruminal atony in calves. Once a week for 4 weeks, each of 6 calves was administered iv 1 treatment of: 0.3 mg of xylazine/kg of body weight, followed in 10 minutes by 1 ml of 0.9% NaCl; 0.3 mg of xylazine/kg, followed in 10 minutes by 3 μg of atipamezole/kg; 0.3 mg of xylazine/kg, followed in 10 minutes by 10 μg of atipamezole/kg; or 0.3 mg of xylazine/kg, followed in 10 minutes by 30 μg of atipamezole/kg. The order of the 4 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 33.6 ±7.1 minutes (mean ± sem-). Atipamezole administered at dosages of 3, 10, and 30 μg/kg shortened xylazine-induced lateral recumbency to 20.5 ± 3.0, 10.2 ± 0.2, and 9.3 ± 0.5 minutes, respectively. Calves given xylazine alone stood at > 60 minutes after the onset of recumbency. Atipamezole given at 3, 10, and 30 μg/kg shortened the time from onset of lateral recumbency to standing to 40.2 ± 6.9, 12.8 ± 1.1, and 10.0 ± 0.7 minutes, respectively. Drowsiness was found in calves given the lowest dosage of atipamezole (3 μg/kg) after the calves stood.

Atipamezole given at dosages of 10 and 30 μg/kg reversed xylazine-induced ruminal atony in a dose-dependent manner. In addition, 30 μg of atipamezole/kg reversed xylazine-induced bradycardia, but the lower dosages of this antagonist did not. Results indicated that 30 μg of atipamezole/kg should be a useful antidote for xylazine overdose in cattle.

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in American Journal of Veterinary Research


Objective—To evaluate baseline plasma cortisol and ACTH concentrations and responses to low-dose ACTH stimulation testing in ill foals.

Design—Cross-sectional study.

Animals—58 ill foals.

Procedures—Baseline cortisol and ACTH concentrations and cortisol concentrations after administration of a low dose of cosyntropin were determined within 6 hours after admission. Foals were assigned to 4 groups on the basis of age (≤ 24 hours vs 1 to 56 days) and presence of septicemia (yes vs no). Values were compared among groups and with values previously reported for healthy foals.

Results—Plasma cortisol concentrations 30 and 60 minutes after cosyntropin administration in foals ≤ 24 hours old were significantly higher than corresponding cortisol concentrations in older foals. In all 4 groups, plasma cortisol concentration 30 minutes after cosyntropin administration was significantly higher than baseline cortisol concentration or concentration 60 minutes after cosyntropin administration. No differences in baseline cor-tisol or ACTH concentration or in the ACTH-to-cortisol ratio were detected between groups or when ill foals were compared with healthy foals. A small number of ill foals had low baseline cortisol and ACTH concentrations or low responses to cosyntropin administration, compared with healthy foals.

Conclusions and Clinical Relevance—Results indicated that most ill foals in the present study population had adequate responses to cosyntropin administration. However, a small subset of ill foals appeared to have dysfunction of the hypothalamic-pituitary-adrenal axis.

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in Journal of the American Veterinary Medical Association


Objective—To evaluate the effect of IV administration of polymyxin B on clinical and serum biochemical variables in foals with experimental endotoxemia.

Design—Prospective experimental study.

Animals—14 healthy neonatal foals.

Procedures—Foals were randomly assigned to a treatment or control group and were administered a single dose of lipopolysaccharide (0.5 μg/kg [0.23 μg/lb]) IV over 30 minutes. The treatment group received polymyxin B (6,000 U/kg [2,727 U/lb], IV) immediately after completion of lipopolysaccharide infusion; the control group was administered an equal volume of saline (0.9% NaCl) solution. Subsequent doses of polymyxin B or saline solution were administered IV at 8 and 16 hours. Blood was collected at various time points, and outcome variables, including heart rate, respiratory rate, rectal temperature, attitude score, WBC count, neutrophil count, lymphocyte count, monocyte count, platelet count, Hct, blood lactate concentration, blood glucose concentration, serum tumor necrosis factor-α concentration, and plasma thromboxane B2 concentration, were measured. Urine was collected prior to and after experimentation to determine whether nephrotoxicosis was associated with treatment.

Results—The treatment group had significantly lower blood lactate concentration and serum tumor necrosis factor-α and plasma thromboxane B2 concentrations and had higher blood glucose concentrations and better attitude scores, compared with the control group, at various time points during the study. No other significant differences and no evidence of overt nephrotoxicosis were detected.

Conclusions and Clinical Relevance—Administration of polymyxin B IV in healthy neonatal foals challenged with lipopolysaccharide attenuated some clinical and serum biochemical derangements associated with endotoxemia.

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in Journal of the American Veterinary Medical Association