Enzyme immunoassay, digoxin

A competitive electrochemical enzyme immunoassay has been demonstrated for digoxin Alkaline phosphatase, which catalyzes the hydrolysis of phenyl phosphate... 

Homogeneous electrochemical enzyme immunoassays for both phenytoin and digoxin have been developed. In both cases the label was glucose-6-phosphate dehydrogenase, which catalyzes the reduction of NAD to NADH. The NADH produced was detected by LCEC at a carbon paste electrode. 

K.R. Wenmeyer, H.B. Halsall, W.R. Heineman, C.P. Voile, and I.W. Chen, Competitive heterogeneous enzyme immunoassay for digoxin with electrochemical detection. Anal. Chem. 58, 135-139 (1986). 

M.Y. Keating and G.A. Rechnitz, Potentiometric enzyme immunoassay for digoxin using polystyrene beads. Anal. Lett. 18, 1-10 (1985). 

E321 Danielson, S.J., Detty, M.R. and Alexandrovich, S.K. (1987). Improved labels for use in digoxin multilayer enzyme immunoassays. Clin. Chem. 33,923, Abstr. 211. 

EN107 Kildal-Brandt, P., Weber, T. and Sutherland, J.W. (1992). Performance on three thin-film enzyme immunoassays Digoxin, phenytoin and phenobarbital using two rate algorithms. Clin. Chem. 38, 1093, Abstr. 681. 

L Nielsen, et al. A sensitive, automated, non-isotopic enzyme immunoassay for the determination of digoxin. Clin Chem 33 1014, 1987. 

SJ Danielson, et al. Improved labels for use in digoxin multilayer enzyme immunoassays. Clin Chem 33 923, 1987. 

The LCEC method in conjunction with the optimal assay parameters resulted in a very sensitive immunoassay for digoxin in plasma throughout its therapeutic range, with a detection limit of 50 pg/ml. A standard curve is shown in Fig. 7. The relative standard deviation of ip obtained for any given digoxin standard ranged from 4% to 12% on various days and is comparable to results ordinarily obtained by other heterogeneous enzyme immunoassays. Approximately 20 samples can be injected per hour. 

Samples from patients receiving digoxin therapy were analyzed by the heterogeneous immunoassay LCEC method. Samples were diluted 5/1 with pooled human plasma in order to eliminate an observed antibody matrix effect. Digoxin standards in pooled human plasma were treated similarly and a standard curve constructed. Digoxin levels in patient samples were determined by reference to the standard curve. The values obtained for the samples by the electrochemical enzyme immunoassay method were compared to those obtained by radioimmunoassay. The results for the 54 samples analyzed are presented in Fig. 8. A good correlation was obtained between the two methods (r = 0.93). 

Fig. 6. Heterogeneous enzyme immunoassay with LCEC detection for a series of digoxin standards in plasma solutions. Concentration of digoxin in plasma samples (A), 5.0, (B) 2.0, (C) 1.0, (D) 0.5, and (E) 0 ng/ml. Assay conditions 10 pg/ml antibody coating concentration, 1/125 digoxin-alkaline phosphatase conjugate dilution, 4 h antigen/antibody incubation interval, and 40 min substrate reaction time. (Reprinted with permission from Wehmeyeretal., 1986. Copyright 1986, American Chemical Society.)...

Fig. 17. Homogeneous enzyme immunoassay with column switching LCEC for digoxin calibrators of marked concentration in ng/ml. —NADH peaks. Enzyme reaction sampled at 2 and 7 min for each calibrator.

In an in vitro study, plantain (Plantago major) extract from capsules, liquid extract, or dry leaf did not affect the results of digoxin assays when using fluorescence polarization immunoassay or microparticle enzyme immunoassay. Note that contamination of plantain with Digitalis lanata has been reported. ... 

Asian or Chinese ginseng (Panax ginseng) and Siberian ginseng (Eleu-therococcus senticosus) have both been found to interfere with some digoxin assays including fluorescence polarisation immunoassay (FPIA) and microparticle enzyme immunoassay (MEIA). ... 

Enzyme immunoassays for digoxin, thyroxine and insulin have been performed with horse radish peroxidase as a label. The antigen-antibody complex was treated with luminol or other related hydrazides, the most efficient being 7-dimethylamino naphthalene-1,2-dicarboxylic acid hydrazide (92) (cf. p. 80) [129]. 

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