Valdes R, Brown B A, Graves S W
Am J Clin Pathol. 1984 Aug;82(2):210-3. doi: 10.1093/ajcp/82.2.210.
The authors investigated the cross-reactivity of the major known digoxin metabolites--digoxigenin, digoxigenin monodigitoxoside, digoxigenin bisdigitoxoside, and dihydrodigoxin--and of digitoxin in three 125I-radioimmunoassays and one enzyme immunoassay for digoxin. Digitoxin and dihydrodigoxin exhibit low cross-reactivity and nonparallel dilution responses for these assays. The cross-reactivities of the other three substances are significant for all assays studied with digoxigenin and monodigitoxoside having nonparallel and enhanced tracer displacement compared with digoxin itself. The authors demonstrate that because of nonparallel tracer displacement estimates of cross-reactivity calculated by the 50% displacement method fail to adequately predict the error induced in digoxin assays by digitoxin. They conclude that digoxin metabolites in serum are measured to various extents as the parent digoxin compound by all of the immunoassays they studied. In view of the varying biologic activity of digoxin metabolites and the large patient to patient variations in digoxin metabolism, the cross-reactivities the authors observe may help to explain the discrepancies in correlation of clinical response to measured serum digoxin values reported in other studies.
作者在三种用于地高辛的125I放射免疫测定法和一种酶免疫测定法中，研究了主要已知地高辛代谢产物——洋地黄毒苷、洋地黄毒苷单洋地黄毒糖甙、洋地黄毒苷双洋地黄毒糖甙和二氢地高辛——以及洋地黄毒苷的交叉反应性。对于这些测定法，洋地黄毒苷和二氢地高辛表现出低交叉反应性和非平行稀释反应。在所有所研究的测定法中，其他三种物质的交叉反应性显著，与地高辛本身相比，洋地黄毒苷和单洋地黄毒糖甙具有非平行且增强的示踪剂置换。作者证明，由于示踪剂置换不平行，通过50%置换法计算的交叉反应性估计值无法充分预测洋地黄毒苷在地高辛测定中引起的误差。他们得出结论，在所研究的所有免疫测定法中，血清中的地高辛代谢产物在不同程度上被测定为母体地高辛化合物。鉴于地高辛代谢产物的生物活性不同以及患者之间地高辛代谢存在较大差异，作者观察到的交叉反应性可能有助于解释其他研究中报道的临床反应与测得的血清地高辛值之间相关性的差异。
