Smith D J, Shelver W L, Marx A
J Anim Sci. 2016 Dec;94(12):5423-5433. doi: 10.2527/jas.2016-0899.
Qualitative assays are sometimes used as the sole basis for detecting drug residues in live animals or in animal products. Such assays have become increasingly sensitive as detection technologies have improved, yet the limitations of such assays to discriminate purposeful and accidental drug exposures remain poorly defined. A study was conducted to determine the ability of a ractopamine lateral flow assay to accurately detect incurred ractopamine residues in contaminated feeds and in sheep fed trace quantities of ractopamine HCl. False positive and negative samples were determined using a quantitative liquid chromatography-tandem mass spectrometric (LC-MS/MS) method. Ractopamine HCl was fed to sheep at 0 (Zero), 1 (Low), 10 (Med), or 100 (High) µg/kg of diet ( = 4 per level, 0.5 kg of feed/d) for 7 consecutive d and urine was collected daily about ∼16 h post exposure. On-site lateral flow assays were able to reliably (0% false negatives) detect 20 μg of ractopamine HCl per kg of feed. Urine from treated sheep tested positive for ractopamine residues by lateral flow assay in 7.4 (Zero), 0 (Low), 82 (Med), and 86% (High) of the urine samples from each group. Parent ractopamine was below the assay limit of quantification (LOQ, 0.7 ng/mL) in all urine samples using LC-MS/MS. After hydrolysis of ractopamine conjugates, total ractopamine (parent + hydrolyzed metabolites) in urine of Low animals was always less than the LOQ, but in 7 of 28 samples were above the limit of detection (LOD, 0.22 ng/mL). In contrast, urine in Med animals contained 1.08 to 9.13 ng/mL of total ractopamine, while urine of High animals contained 4.85-32.82 ng/mL of total ractopamine. Ractopamine is rapidly eliminated; nevertheless, > 80% of urine samples from sheep exposed to 5 µg/d (M) of ractopamine HCl had detectable residues by the screening assay and a 100% of samples had measurable ractopamine using LC-MS/MS methods. Tissue residues of ractopamine were not detected in any of the sheep. The sensitivity with which the rapid, qualitative assay detected ractopamine was sufficient to reveal trace ractopamine exposures; these data suggest that the use of qualitative tests to indicate purposeful treatment of animals (i.e., for doping or growth enhancement), in the absence of collaborating quantitative data, is inappropriate.
定性检测有时被用作检测活体动物或动物产品中药物残留的唯一依据。随着检测技术的改进，此类检测的灵敏度越来越高，但此类检测在区分有意和意外药物暴露方面的局限性仍未得到明确界定。开展了一项研究，以确定莱克多巴胺侧向流动检测法准确检测受污染饲料和摄入微量盐酸莱克多巴胺的绵羊体内莱克多巴胺残留的能力。使用定量液相色谱 - 串联质谱法（LC - MS/MS）确定假阳性和阴性样本。以0（零）、1（低）、10（中）或100（高）μg/kg的日粮水平给绵羊饲喂盐酸莱克多巴胺（每个水平 = 4只，每天0.5 kg饲料），连续7天，每天在接触后约16小时收集尿液。现场侧向流动检测能够可靠地（假阴性率为0%）检测出每千克饲料中20μg的盐酸莱克多巴胺。通过侧向流动检测，每组绵羊尿液样本中，来自接受0（零）μg/kg、1（低）μg/kg、10（中）μg/kg和100（高）μg/kg盐酸莱克多巴胺处理的绵羊的尿液中，莱克多巴胺残留检测呈阳性的比例分别为7.4%、0%、82%和86%。使用LC - MS/MS法检测，所有尿液样本中母体莱克多巴胺均低于检测限（LOQ，0.7 ng/mL）。莱克多巴胺结合物水解后，低剂量组动物尿液中的总莱克多巴胺（母体 + 水解代谢物）始终低于LOQ，但28个样本中有7个高于检测限（LOD，0.22 ng/mL）。相比之下，中剂量组动物尿液中总莱克多巴胺含量为1.08至9.13 ng/mL，高剂量组动物尿液中总莱克多巴胺含量为4.85 - 32.82 ng/mL。莱克多巴胺迅速被清除；然而，接触5μg/d（中剂量）盐酸莱克多巴胺的绵羊，超过80%的尿液样本通过筛查检测有可检测到的残留，使用LC - MS/MS法检测，100%的样本中有可测量的莱克多巴胺。在任何一只绵羊中均未检测到莱克多巴胺的组织残留。快速定性检测法检测莱克多巴胺的灵敏度足以揭示微量莱克多巴胺暴露；这些数据表明，在没有配套定量数据的情况下，使用定性检测来表明对动物的有意处理（即用于兴奋剂或生长促进）是不合适的。
