Dexamethasone is approved for cattle in Canada for several conditions, but no withdrawal times are currently provided on the approved labels. Recently, the list of Maximum Residues Limits for Veterinary Drugs in Foods in Canada was amended to include dexamethasone. The objectives of this study were to determine the residue depletion profile of dexamethasone after an extra-label dosage regimen in milk of healthy lactating dairy cattle (n = 18) and in edible tissues of healthy beef cattle (n = 16) and to suggest withdrawal intervals. Dexamethasone was administered intramuscularly at 0.05 mg/kg daily for 3 days. Milk samples were collected prior to treatment and every 12 h up to 96 h post-dose. Muscle, liver, kidney, and peri-renal fat tissues were collected from beef cattle at 3, 7, 11, or 15 days post-dose. Dexamethasone analysis was performed by liquid chromatography/mass spectrophotometry. Dexamethasone residues were detected in milk samples up to 36 h. Muscle and fat had no detectable dexamethasone residues while kidney and liver had detectable residues only on day 3 post-dose. A withdrawal interval of 48 h for milk in Canadian dairy cattle and 7 days for meat in Canadian beef cattle are suggested for the dexamethasone treatment regimen most commonly requested to CgFARAD™.

中文翻译：

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牛体内地塞米松的消耗：奶牛和肉牛的食品安全研究

地塞米松在加拿大被批准用于牛治疗多种疾病，但批准的标签上目前没有提供停药时间。最近，加拿大食品中兽药最大残留限量清单进行了修订，将地塞米松纳入其中。本研究的目的是确定在健康泌乳奶牛 ( n  = 18) 的牛奶和健康肉牛 ( n = 16) 的可食用组织中采用标签外剂量方案后地塞米松的残留消除情况， 并建议停药间隔。每天肌肉注射地塞米松 0.05 mg/kg，持续 3 天。在治疗前和给药后每 12 小时收集一次牛奶样品，直至给药后 96 小时。在给药后 3、7、11 或 15 天从肉牛收集肌肉、肝脏、肾脏和肾周围脂肪组织。通过液相色谱/质谱法进行地塞米松分析。牛奶样品中检测到地塞米松残留长达 36 小时。肌肉和脂肪中没有检测到地塞米松残留，而肾脏和肝脏仅在给药后第 3 天有可检测到的残留。对于 CgFARAD™ 最常要求的地塞米松治疗方案，建议加拿大奶牛的停奶间隔为 48 小时，加拿大肉牛的停奶间隔为 7 天。