Apparent Digoxin Research Articles

Convallatoxin, the active cardiac glycoside of lily of the valley, minimally affects the ADVIA Centaur digoxin assay

Lily of the valley is a poisonous plant due to the presence of the cardiac glycoside convallatoxin which is known to interfere with serum digoxin measurement using the LOCI digoxin assay and other digoxin assays. We evaluated potential interference of convallatoxin as well as extract of lily of the valley with the ADVIA Centaur digoxin assay by comparing results obtained using the LOCI digoxin assay. Aliquots of a drug-free serum pool and a digoxin serum pool were supplemented with nanograms to 1μg quantities of convallatoxin or 1.0 and 2.5μL of lily of the valley extract per milliliter of serum followed by measurement of digoxin concentrations using the LOCI and ADVIA Centaur digoxin assays. Apparent digoxin concentrations were minimal using the ADVIA Centaur digoxin assay when aliquots of drug-free serum were supplemented with convallatoxin or extract of lily of the valley but apparent digoxin levels were very high using the LOCI digoxin assay. Moreover, minimal interference in serum digoxin measurement using the ADVIA Centaur digoxin assay was observed when aliquots of serum digoxin pool were further supplemented with lily of the valley extract. As expected, the LOCI digoxin assay showed significant interference of convallatoxin in serum digoxin measurement. Significant interference of convallatoxin in serum digoxin measurement using the LOCI digoxin assay could be minimized using the ADVIA Centaur digoxin assay.

Comparison of LOCI Digoxin Assay and iDigoxin Assay for Rapid Detection of Convallatoxin, the Active Glycoside of the Lily of the Valley Plant

ObjectiveLily of the Valley is a poisonous plant, used as an herbal remedy, with toxic effects due to convallatoxin, a cardiac glycoside. It has been reported that the LOCI digoxin assay, a luminescent oxygen channeling based digoxin immunoassay, has sufficient cross reactivity with Lily of the Valley extract, and the specific toxic component, convallatoxin. Yet, cross reactivity by the iDigoxin immunoassay, a chemiluminescent microparticle immunoassay, has not been reported in the literature. In this study, we evaluate iDigoxin immunoassay's ability to detect Lily of the Valley and convallatoxin, and compare these findings to those measured by the LOCI digoxin assay.Materials and MethodsAliquots of drug free and digoxin serum pools were supplemented with microliter amounts of Lily of the Valley extract or nanogram quantities of convallatoxin. Digoxin concentrations were measured using the iDigoxin immunoassay applied to the ARCHITECT i2000SR analyzer (Cabbott Laboratories), and the LOCI digoxin assay applied to the Vista 1500 analyzer (Siemens Diagnostics).ResultsThe iDigoxin assay measured significantly higher apparent digoxin concentrations than the LOCI digoxin assay in all supplemented aliquots. Also, the LOCI digoxin assay demonstrated bi‐directional interference with aliquots of a digoxin pool supplemented with various amounts of convallatoxin. However, with the iDigoxin assay all values were falsely elevated, indicating positive interference only.ConclusionsThe iDigoxin assay can be used for rapid detection of convallatoxin and Lily of the Valley in human serum. Also, the iDigoxin assay is more sensitive than the LOCI digoxin assay in convallatoxin detection.

Rapid detection of the active cardiac glycoside convallatoxin of lily of the valley using LOCI digoxin assay.

To explore the luminescent oxygen channeling technology-based digoxin immunoassay (LOCI digoxin assay) for rapid detection of lily of the valley extract and convallatoxin. The potential in vitro binding of convallatoxin with Digibind was also evaluated. Aliquots of a drug-free serum pool and a digoxin serum pool were supplemented with lily of the valley extract or convallatoxin, and then apparent digoxin concentrations were measured using the LOCI digoxin assay. Mice were administered lily of the valley extract or 50 μg of convallatoxin, and digoxin concentrations in serum specimens were measured 1 and 2 hours after gavage. Aliquots of a serum pool supplemented with convallatoxin or lily of the valley extract were further supplemented with various concentrations of Digibind and free apparent digoxin concentrations were measured. Apparent digoxin concentrations were observed when aliquots of a drug-free serum pool were supplemented with convallatoxin or lily of the valley extract, and also with convallatoxin or herbal extract. Bidirectional interference of convallatoxin and lily of the valley extract with serum digoxin measurement using the LOCI assay was also observed. Digibind was capable of binding convallatoxin in vitro. LOCI digoxin assay can be used for rapid detection of convallatoxin, and Digibind can bind convallatoxin in vitro.

Rapid detection of convallatoxin using five digoxin immunoassays

Context. Cardiac glycosides of plant origin are implicated in toxic ingestions that may result in hospitalization and are potentially lethal. The utility of commonly available digoxin serum assays for detecting foxglove and oleander ingestion has been demonstrated, but no studies have evaluated the structurally similar convallatoxin found in Convallaria majalis (lily of the valley) for rapid laboratory screening, nor has digoxin immune Fab been tested as an antidote for this ingestion. Objective. We aimed to (1) evaluate multiple digoxin assays for cross-reactivity to convallatoxin, (2) identify whether convallatoxin could be detected in vivo at clinically significant doses, and (3) determine whether digoxin immune Fab could be an effective antidote to convallatoxin. Materials and methods. Cross-reactivities of purified convallatoxin and oleandrin with five common digoxin immunoassays were determined. Serum from mice challenged with convallatoxin was tested for apparent digoxin levels. Binding of convallatoxin to digoxin immune Fab was determined in vitro. Results. Both convallatoxin and oleandrin were detectable by a panel of commonly used digoxin immunoassays, but cross-reactivity was variable between individual assays. We observed measurable apparent digoxin levels in serum of convallatoxin intoxicated mice at sublethal doses. Convallatoxin demonstrated no binding by digoxin immune Fab. Conclusion. Multiple digoxin immunoassays detect botanical cardiac glycosides including convallatoxin and thus may be useful for rapid determination of severe exposures, but neutralization of convallatoxin by digoxin immune Fab is unlikely to provide therapeutic benefit.

Effect of Chinese Medicine Danshen and Indian Ayurvedic Medicine Bark of Arjuna Tree on a Relatively New LOCI Digoxin Assay for Application on the Vista 1500 Analyzer.

Danshen is a traditional Chinese medicine and bark of Arjuna tree is an Ayurvedic medicine both indicated as heart tonic. Interference of Danshen in serum digoxin immunoassays has been reported but potential interference of extract of bark of Arjuna tree has not been reported. We studied potential interferences of Danshen and bark of Arjuna tree on a relatively new LOCI digoxin assay for application on the Vista 1500 analyzer (Siemens Diagnostics). Aliquots of drug-free serum were supplemented with ethyl acetate extract of Danshen (two different brands studied) or aqueous or ethyl alcohol extract of bark of Arjuna tree and apparent digoxin concentrations were measured by the LOCI digoxin assay. In another experiment, aliquots of serum pool containing digoxin were further supplemented with Danshen or bark of Arjuna tree extract and digoxin concentrations were measured again using LOCI digoxin assay. Little apparent digoxin concentration was observed when aliquots of drug-free serum pools were supplemented with Danshen or bark of Arjuna tree extract. When aliquots of serum digoxin pool were further supplemented with these extract, we observed statistically significant negative interference but such differences may not be clinically significant. We conclude that LOCI digoxin assay is virtually free from interferences of Danshen and extract of bark of Arjuna tree.

Digoxin Immunoassays on the ARCHITECT i2000SR and ARCHITECT c8000 Analyzers Are Free From Interferences of Asian, Siberian, and American Ginseng

Asian, Siberian, and American ginseng are known to interfere with serum digoxin measurements using fluorescence polarization technology, Digoxin II and Digoxin III assays (Abbott Laboratories, Green oaks, IL) as well as other digoxin assays. Abbott Laboratories more recently launched two new digoxin assays: iDigoxin, a chemiluminescent microparticle immunoassay for application on the ARCHITECT i1000SR and i2000SR immunoassay analyzers, and cDigoxin, a particle-enhanced turbidimetric inhibition immunoassay for application on the ARCHITECT c4000, c8000, and c1600 clinical chemistry analyzers; and we studied potential interferences of ginsengs with these two assays in vitro. When aliquots of drug-free serum pool treated with activated charcoal were supplemented with extracts of various ginsengs, no significant apparent digoxin values were observed. In addition, when aliquots of the digoxin pool prepared from patients taking digoxin were further supplemented with these ginseng extracts and the digoxin values were re-measured, we observed no statistically significant difference in observed digoxin values compared to the original digoxin value of the pool. These results further establish that relatively new digoxin assays for application on the ARCHITECT analyzers that employ specific monoclonal antibodies against digoxin are free from interferences from Asian, Siberian, and American ginseng.

Bidirectional (Negative/Positive) Interference of Oleandrin and Oleander Extract on a Relatively New LOCI Digoxin Assay Using Vista 1500 Analyzer

Oleander interferes with serum digoxin measurements using various immunoassays. The potential interference of oleander and its active ingredient, oleandrin, with a relatively new homogenous sequential chemiluminescent digoxin assay based on luminescent oxygen channeling technology (LOCI digoxin assay, Siemens Diagnostics) has not been previously reported. Aliquots of a digoxin-free serum pool were supplemented with increasing concentrations of oleandrin, or with oleander extract, followed by measuring the apparent digoxin concentrations using the LOCI digoxin assay using Vista 1500 analyzer. Mice were fed oleandrin or oleander extract, and their blood digoxin levels at 1 and 2 h were measured with the LOCI digoxin assay. In addition, two digoxin serum pools were prepared by combining sera of patients receiving digoxin; aliquots of both pools were supplemented with oleandrin or oleander extract and digoxin concentrations were again measured. Attempts to overcome this interference were made by measuring free digoxin concentration using a third digoxin pool. Significant apparent digoxin concentrations were observed after supplementing aliquots of the drug-free serum pool with oleandrin or oleander extract. Mice fed with oleandrin or oleander extract also showed apparent digoxin levels 1 and 2 h after feeding. Digoxin values were also falsely lower or elevated (bidirectional interference) when aliquots of digoxin serum pools were further supplemented with oleandrin or oleander extract depending on concentration; this interference was not eliminated by free digoxin monitoring. Oleandrin interferes with LOCI digoxin assay.

The New LOCI Digoxin Assay on the Vista 1500 Analyzer Is Virtually Free From Interferences of Herbal Supplements Hawthorn and Ashwagandha (Indian Ginseng)

Herbal supplements hawthorn and ashwagandha (Indian ginseng) are indicated for cardiac illnesses and may be taken by patients receiving digoxin therapy. Because both hawthorn and ashwagandha are known to interfere with serum digoxin measurements using certain digoxin immunoassays, we investigated potential interference of these two herbal supplements with the new homogenous sequential chemiluminescent assay for digoxin based on the luminescent oxygen channeling technology (LOCI digoxin) for application on the Dimension and Vista platform. When aliquots of a drug-free serum pool were supplemented with various amounts of hawthorn (three different commercial preparations) or ashwagandha (two different commercial preparations) and apparent digoxin values were measured using LOCI digoxin assay on Dimension Vista 1500 analyzer we observed none-detected values except when aliquots were supplemented with very high amounts of the herbal extracts. When aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin) where further supplemented with various amounts of these supplements and digoxin concentrations were remeasured, statistically significant falsely higher digoxin values were observed only in specimens containing very high amounts of these supplements. Such interference may not be clinically significant. We conclude that new LOCI digoxin assay is virtually free from interferences of herbal supplements, hawthorn, and ashwagandha.

Clinically Insignificant Negative Interferences of Spironolactone, Potassium Canrenoate, and Their Common Metabolite Canrenone in New Dimension Vista LOCI Digoxin Immunoassay

Spironolactone, a potassium-sparing diuretic metabolized to canrenone is often used with digoxin to treat various conditions including congestive heart failure. Potassium canrenoate is a similar drug, which is also metabolized to canrenone. Due to reported both positive and negative interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with the new homogenous sequential chemiluminescent assay for digoxin based on the luminescent oxygen channeling technology (LOCI digoxin) for application on the Dimension and Vista platform. When aliquots of a drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and apparent digoxin values were measured using Dimension Vista LOCI digoxin assay, we observed no detected value except when aliquots were supplemented with very high amounts of potassium canrenoate or canrenone. However, we observed that apparent digoxin concentrations were very low. When aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin), were further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and serum digoxin concentrations were remeasured using the LOCIdigoxin assay, only statistically significant falsely lower digoxin values (negative interference) were observed in specimens containing very high amounts of canrenone or potassium canrenoate. However, such small bias may not have any clinical significance. We conclude that new Dimension Vista LOCI digoxin assay is virtually free from interferences of spironolactone, potassium canrenoate, and their common metabolite canrenone.

Effect of Chinese Medicines Chan Su, Asian Ginseng, Siberian Ginseng, and American Ginseng on a New Digoxin Immunoassay Based on Luminescent Oxygen Channeling Technology

Chan Su, Asian ginseng, Siberian ginseng, and American ginseng are known to interfere with various digoxin immunoassays. Recently, a homogeneous sequential chemiluminescent assay for digoxin based on the luminescent oxygen channeling technology (LOCI digoxin) for application on the Dimension and Vista platform has been introduced into the market. The effects of interference by Chan Su and various ginsengs on this new immunoassay have not yet been reported. Aliquots of a drug-free serum pool were supplemented with Chan Su, Asian ginseng, Siberian ginseng, and American ginseng representing the expected in vivo concentrations after normal usage and cases of overdose. Serum digoxin concentrations were measured using the LOCI digoxin assay on the Vista 1500 analyzer. We also prepared 3 digoxin pools from patients receiving digoxin. Two digoxin pools were supplemented with these traditional medicines to investigate their effect on serum digoxin measurements. Mice were fed Chan Su extract to determine the potential of in vivo derived interfering factors. The possibility of eliminating interference of Chan Su on serum digoxin measurement was also investigated, by measuring free digoxin concentration after supplementing aliquots of the third digoxin pool with various amounts of Chan Su extract. A clinically significant interference by Chan Su with serum digoxin measurement was observed using the LOCI digoxin assay. The various ginsengs demonstrated negligible effects. In addition, apparent digoxin concentrations were observed in sera of mice after feeding them with Chan Su; the half-life of digoxin-like immunoreactive components was approximately 1 hour. Moreover, serum digoxin concentrations were significantly elevated in the presence of Chan Su, whereas the various ginsengs exhibited no effect. Monitoring free digoxin can only partly eliminate the interference of Chan Su in serum digoxin measurement. Chan Su interferes with serum digoxin measurement using the LOCI Digoxin, whereas the ginsengs demonstrated no measurable interference at clinically relevant concentrations.

Abbott ARCHITECT Clinical Chemistry and Immunoassay Systems: Digoxin Assays Are Free of Interferences From Spironolactone, Potassium Canrenoate, and Their Common Metabolite Canrenone

Spironolactone, which is metabolized to canrenone, is often used in combination with digoxin. Potassium canrenoate is a similar drug that is also metabolized to canrenone. As a result of reported interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with two relatively new digoxin assays for application on ARCHITECT clinical chemistry platforms (cDig, particle-enhanced turbidimetric inhibition immunoassay) and ARCHITECT immunoassay platforms (iDig, chemiluminescent microparticle immunoassay), both from Abbott Diagnostics. When aliquots of drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, and canrenone, no apparent digoxin concentration was observed using cDig assay on ARCHITECT c4000, c8000, and c16000 or iDig assay on i1000SR and i2000SR analyzers. In addition, we observed no false increase in serum digoxin value when aliquots of a digoxin pool were further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone. We conclude that both the cDig and iDig assays on the ARCHITECT analyzers are free from interferences by spironolactone, potassium canrenoate, and canrenone.

Rapid detection of oleander poisoning by Dimension Vista digoxin assay (Flex Reagent Cartridge)

Oleander poisoning can be detected by digoxin immunoassays and for last two decades the fluorescence polarization immunoassay (FPIA) has been used for rapid detection of oleander poisoning in clinical laboratories. Recently, Abbott Laboratories (Abbott Park, IL) discontinued this assay. Therefore, we explored the possibility of using another digoxin assay (Dimension Vista Flex Reagent Cartridge, Tina Quant, EMIT 2000 and old FPIA assay for comparison) for rapid detection of oleander poisoning. When aliquots of drug-free serum pools were supplemented with pure oleandrin or oleander extract, we observed the highest apparent digoxin values using Dimension Vista digoxin assay (Flex Reagent Cartridge). We also observed significant apparent digoxin values in vivo in sera of mice both 1 and 2 hr after feeding with oleander extract. When a serum pool prepared from patients taking digoxin was further supplemented with various amounts of oleander extract, the highest falsely elevated digoxin values were observed with Dimension Vista digoxin assay. Monitoring free digoxin using Dimension Vista digoxin assay (Flex Reagent Cartridge) did not eliminate this interference. Digibind neutralized digoxin-like factors of oleander extract and such effect can be monitored by observing significant reduction in apparent free digoxin levels in the presence of Digibind as measured in the protein-free ultrafiltrate using Dimension Vista digoxin assay (Flex Reagent Cartridge).

Interference Between Eplerenone and Digoxin in Fluorescence Polarization Immunoassay, Microparticle Enzyme Immunoassay, and Affinity Column-Mediated Immunoassay

Digitalis-like immunoreactive substances have crossreactivity with antidigoxin antibodies and the interference between digoxin and spironolactone/canrenone has been reported. The structure of eplerenone is similar to that of spironolactone/canrenone. Therefore, we hypothesized that eplerenone might also interfere with the measurement of digoxin by immunoassay. We performed three types of assays (fluorescence polarization immunoassay [FPIA], microparticle enzyme immunoassay [MEIA], and affinity column-mediated immunoassay [ACMIA]) to determine crossreactions between eplerenone and antidigoxin antibodies. Furthermore, we used FPIA, MEIA, and ACMIA to measure the apparent digoxin concentration in mixed solutions of eplerenone (1-100 μg/mL) and digoxin (1-3 ng/mL). In the crossreaction tests, eplerenone was detected as digoxin by FPIA and ACMIA. By FPIA, a known concentration of 1 μg/mL of eplerenone was measured as 0.33 ± 0.11 ng/mL of digoxin (crossreaction rate, 0.03%). By ACMIA, a known concentration of 10 μg/mL of eplerenone was measured as 0.13 ± 0.05 ng/mL of digoxin (crossreaction rate, 0.001%). No crossreaction between eplerenone and digoxin was determined by MEIA. In the interference of eplerenone coadministered with digoxin, the apparent concentration of digoxin was increased in FPIA, but decreased in MEIA and ACMIA. The results suggest that eplerenone crossreacts with antidigoxin antibodies in FPIA, MEIA, and ACMIA, but that the interference of eplerenone might be smaller than that of spironolactone/canrenone.

Effect of spironolactone, potassium canrenoate, and their common metabolite canrenone on dimension Vista Digoxin Assay

Spironolactone, a potassium sparing diuretic metabolized to canrenone, is often used with digoxin to treat various conditions including congestive heart failure. Potassium canrenoate is a similar drug that is also metabolized to canrenone. Due to reported interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with Dimension Vista Digoxin immunoassay using Flex reagent cartridge. Aliquots of a drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and apparent digoxin values were measured using Dimension Vista digoxin assay, we observed none-detected value except when aliquots were supplemented with higher amounts of spironolactone or canrenone. Similarly, when aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin) where further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone, we observed moderately falsely elevated digoxin values only in specimens containing higher amounts of spironolactone or canrenone. We conclude that spironolactone and canrenone but not potassium canrenoate may cause modest interference with Dimension Vista digoxin assay but such interferences may not be clinically significant except with very high amounts of canrenone.

Effect of Spironolactone, Potassium Canrenoate and Their Common Metabolite Canrenone on Serum Digoxin Measurement by Digoxin III, a New Digoxin Immunoassay

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are often used with digoxin in clinical practice. It has been well documented in the literature that spironolactone, potassium canrenoate, and their common metabolite canrenone cross-react with several digoxin immunoassays at concentrations expected after therapeutic usage of these drugs and falsely elevate or lower serum digoxin concentrations. Recently, Abbott Laboratories marketed a new Digoxin III immunoassay for application on the AxSYM analyzer. We studied the potential interference of these compounds with this new digoxin assay. The Tina-quant assay was used as the reference method because spironolactone, potassium canrenoate, and canrenone do not interfere with serum digoxin measurement using this assay. Aliquots of drug-free serum were supplemented with therapeutic and above therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin concentrations were measured using the Digoxin III assay and Tina-quant assay. Significant apparent digoxin concentrations were observed when the Digoxin III digoxin assay was used, but no apparent digoxin levels was observed using the Tina-quant assay. When serum pools prepared from patients receiving digoxin were further supplemented with these compounds in concentrations expected in sera of patients receiving these medications, falsely elevated digoxin levels were observed using Digoxin III assay, but no statistically significant change was observed using the Tina-quant assay. We conclude that spironolactone, potassium canrenoate, and their common metabolite canrenone interfere with the serum digoxin measurements using the new Digoxin III assay.

Measuring the Unbound Concentration Fails to Resolve Analytic Interferences in Digoxin Immunoassays

Therapeutic drug monitoring of digoxin is well established in the clinical management of cardiac patients treated with the drug. Recently, target concentrations have been revised in patients with congestive heart failure to 0.5 to 0.8 microg/L, challenging the sensitivity limits of most immunoassays. These widely used methods are often criticized, particularly on specificity grounds resulting from interference from exogenous and endogenous sources. One solution to remove higher molecular weight interference has been to ultrafilter plasma samples before assaying. The present study included 261 patient digoxin samples and compared two commercial ultrafiltration devices (Centrifree and Micrcon) that share the same separation membrane (YM-30). The results showed widely discordant apparent unbound digoxin concentrations in the ultrafiltrate from these devices with a Deming regression line of Centrifree = 1.31 x Micrcon + 0.042 (95% confidence interval for slope of 1.237 to 1.391) and apparent unbound fractions ranging from 15% to 610% of the unfiltered plasma digoxin concentrations, suggesting that ultrafiltration did not resolve such interference issues. The concept of measuring lower unbound digoxin concentrations as a result of lower therapeutic range for total (bound plus unbound) digoxin will also render most immunoassays insensitive and inappropriately calibrated. There is a strong imperative to review digoxin monitoring practices in the light of current clinical imperatives for both specificity and sensitivity reasons.

Rapid Detection of Oleander Poisoning by Digoxin III, a New Digoxin Assay

We studied the potential for detecting oleander with a new immunoassay (Digoxin III, Abbott Laboratories, Abbott Park, IL) by comparing results with those from the fluorescence polarization immunoassay (FPIA) and Digoxin II assay (Abbott). In aliquots of drug-free serum pools supplemented with pure oleandrin or oleander extract, we observed apparent digoxin values using all 3 immunoassays, but values obtained by the Digoxin III were higher than obtained by the other assays. We also observed significant apparent digoxin values in vivo in serum samples of mice 1 and 2 hours after feeding oleander extract. The average half-life of digoxin-like factors was 1.1 hours. In a serum pool (prepared from patients taking digoxin) supplemented with oleander extract, the observed digoxin values were falsely lowered when measured by the Digoxin II but falsely elevated when measured by the Digoxin III and FPIA. Monitoring free digoxin using the Digoxin III cannot eliminate this interference. Digibind neutralized digoxin-like factors of oleander extract; the effect can be monitored by observing a significant reduction in apparent free digoxin levels in the presence of Digibind as measured in protein-free ultrafiltrate using the Digoxin III. The Digoxin III is highly sensitive for measuring oleander.

Effect of Chinese Medicines Chan Su and Lu-Shen-Wan on Serum Digoxin Measurement by Digoxin III, a New Digoxin Immunoassay

Chan Su and Lu-Shen-Wan are Chinese medicines that crossreact with digoxin immunoassays. Recently, Abbott Laboratories released a new digoxin immunoassay, Digoxin III. We studied potential interference of Chan Su and Lu-Shen-Wan with the Digoxin III assay by comparing results obtained by using Digoxin II and fluorescence polarization immunoassay, also manufactured by Abbott Laboratories. Aliquots of a drug-free serum pool were supplemented with aqueous extract of Chan Su or Lu-Shen-Wan and apparent digoxin concentrations were measured using all three digoxin assays. Significant crossreactivity of Chan Su and Lu-Shen-Wan was observed with the new Digoxin III assay. Moreover, when mice were fed with Chan Su or Lu-Shen-Wan, significant apparent digoxin concentrations were also observed in the sera of mice using the Digoxin III assay indicating that such interferences are also present in vivo. When serum pools prepared from patients receiving digoxin were further supplemented with Chan Su or Lu-Shen-Wan extract, falsely elevated digoxin values were observed with both Digoxin III and fluorescence polarization immunoassay, but digoxin values were falsely lowered using the Digoxin II assay. For example, when one aliquot of Digoxin Serum Pool 1 containing 0.94 ng/mL of digoxin was supplemented with 5.0 microg/mL of Chan Su extract, the digoxin concentration was falsely elevated to 6.60 ng/mL as measured by the Digoxin III assay and 6.99 as measured by the fluorescence polarization immunoassay assay. In contrast, the observed digoxin value was falsely lowered to 0.72 ng/mL using the Digoxin II assay. Interference of Chan Su and Lu-Shen-Wan in the Digoxin III assay cannot be eliminated by monitoring free digoxin concentrations. Digibind neutralizes digoxin-like immunoreactive components of Chan Su and such effect can be monitored by measuring apparent free digoxin concentrations using the Digoxin III assay. We conclude the both Chan Su and Lu-Shen-Wan significantly interfere with serum digoxin measurements by the new Digoxin III assay.

Effect of Asian ginseng, Siberian ginseng, and Indian ayurvedic medicine Ashwagandha on serum digoxin measurement by digoxin III, a new digoxin immunoassay

Asian ginseng, Siberian ginseng, and Indian Ayurvedic medicine Ashwagandha demonstrated modest interference with serum digoxin measurements by the fluorescent polarization immunoassay (FPIA). Recently, Abbott Laboratories marketed a new digoxin immunoassay, Digoxin III for application on the AxSYM analyzer. We studied potential interference of these herbal supplements on serum digoxin measurement by Digoxin III assay in vitro and compared our results with the values obtained by Tina-quant assay. Aliquots of drug-free serum pool were supplemented with various amounts of Asian ginseng, Siberian ginseng, or Ashwagandha approximating expected concentrations after recommended doses and overdoses of these herbal supplements in serum. Then digoxin concentrations were measured by the Digoxin III and Tina-quant (Roche Diagnostics) assay. We also supplemented aliquots of a digoxin pool prepared from patients receiving digoxin with various amounts of these herbal supplements and then measured digoxin concentrations again using both digoxin immunoassays. We observed modest apparent digoxin concentrations when aliquots of drug-free serum pool were supplemented with all three herbal supplements using Digoxin III assay (apparent digoxin in the range of 0.31-0.57 ng/ml), but no apparent digoxin concentration (except with the highest concentration of Ashwagandha supplement for both brands) was observed using the Tina-quant assay. When aliquots of digoxin pool were further supplemented with these herbal supplements, digoxin concentrations were falsely elevated when measured by the new Digoxin III assay. For example, we observed 48.2% (1.63 ng/ml digoxin) increase in digoxin concentration when an aliquot of Digoxin pool 1 (1.10 ng/ml digoxin) was supplemented with 50 microl of Asian ginseng extract (Brand 2). Measuring free digoxin does not eliminate the modest interferences of these herbal supplements in serum digoxin measurement by the Digoxin III assay.

Stability of oleander extract and oleandrin in sera stored in plastic serum separator tubes

Oleander poisoning is common in the southern parts of the United States as well as part of Europe and South East Asia. The fluorescence polarization immunoassay (FPIA) for digoxin cross-reacts with oleandrin, the major poison of oleander extract and can be used for rapid detection of oleander poisoning. However, for medicolegal investigation, the presence of oleandrin should be confirmed by a more sophisticated analytical technique such as liquid chromatography combined with tandem mass spectrometry. We studied stability of oleander extract as well as oleandrin in serum samples stored in Becton Dickinson plastic serum separator tubes (SSTs) by comparing values obtained in parallel specimens stored in plain glass tubes and in red-topped plastic tubes. Oleander leaves were extracted using absolute ethanol, and drug-free serum pools were supplemented with oleander extract or ethanolic solution of pure oleandrin. Aliquots of the supplemented pools were then stored in plain glass tubes, red-topped plastic tubes or SSTs and the stability of oleander extract or oleandrin in sera were studied by the FPIA digoxin assay for varying times up to seven days. We observed no statistically significant change in apparent digoxin concentrations in specimens stored in SSTs even after seven days of storage compared to original values observed in the supplemented serum pools. Specimens can be stored in SSTs for up to seven days prior to analysis of oleandrin concentration.