A simple and sensitive LC-MS/MS method for therapeutic drug monitoring of digoxin in children

This short communication introduced a simple and sensitive LC-MS/MS method for therapeutic drug monitoring of digoxin in children with the lower limit of quantitation of 0.2 ng/mL based on 30 μL of plasma. The plasma sample was pretreated by one-step protein precipitation. Then the chromatographic separation was performed on a short C-18 column with a total run time of 2.4 min. The detection was achieved through multiple reaction monitoring using positive ionization mode on a triple quadrupole mass spectrometer. The linear range of digoxin in human plasma was among 0.2-6.4 ng/mL. The intra-day and inter-day accuracies of digoxin ranged from -6.0 % to 10.1 % and imprecisions were less than 8.8 %. The extraction recovery rate of digoxin in plasma samples was above 90 %. Matrix factor normalized by internal standard was within acceptance criteria. This method was fully verified and applied to determine the plasma digoxin concentrations of 43 pediatric patients. It is approved appropriate and practical for the therapeutic drug monitoring of digoxin in routine clinical laboratory practice, especially for children.

Nanostructured particles assembled from natural building blocks for advanced therapies

Advanced treatments based on immune system manipulation, gene transcription and regulation, specific organ and cell targeting, and/or photon energy conversion have emerged as promising therapeutic strategies against a range of challenging diseases. Naturally derived macromolecules (e.g., proteins, lipids, polysaccharides, and polyphenols) have increasingly found use as fundamental building blocks for nanostructured particles as their advantageous properties, including biocompatibility, biodegradability, inherent bioactivity, and diverse chemical properties make them suitable for advanced therapeutic applications. This review provides a timely and comprehensive summary of the use of a broad range of natural building blocks in the rapidly developing field of advanced therapeutics with insights specific to nanostructured particles. We focus on an up-to-date overview of the assembly of nanostructured particles using natural building blocks and summarize their key scientific and preclinical milestones for advanced therapies, including adoptive cell therapy, immunotherapy, gene therapy, active targeted drug delivery, photoacoustic therapy and imaging, photothermal therapy, and combinational therapy. A cross-comparison of the advantages and disadvantages of different natural building blocks are highlighted to elucidate the key design principles for such bio-derived nanoparticles toward improving their performance and adoption. Current challenges and future research directions are also discussed, which will accelerate our understanding of designing, engineering, and applying nanostructured particles for advanced therapies.

Distinct mechanism of action for antitumoral neutral cyclometalated Pt(II)-complexes bearing antifungal imidazolyl-based drugs

Three neutral Pt(II) complexes containing 1-Methylimidazole and the antifungal imidazolyl drugs Clotrimazole and Bifonazole have been prepared. The general formula of the new derivatives is [Pt(κ²-(C^N)Cl(L)], where C^N stands for ppy = 2-phenylpyridinate, and L = 1-Methylimidazole (MeIm) for [Pt-MeIm]; L = Clotrimazole (CTZ) for [Pt-CTZ] and L = Bifonazole (BFZ) for [Pt-BFZ]). The complexes have been completely characterized in solution and the crystal structures of [Pt-BFZ] and [Pt-CTZ] have been resolved. Complexes [Pt-MeIm] and [Pt-BFZ] present higher cytotoxicity than cisplatin in SW480 (colon adenocarcinoma), A549 (lung adenocarcinoma) and A2780 (ovarian cancer) cell lines. [Pt-MeIm] shows the highest accumulation in A549 cells, in agreement with its inability to interact with serum albumin. By contrast, [Pt-CTZ] and [Pt-BFZ] interact with serum proteins, a fact that reduces their bioavailability. The strongest interaction with bovine serum albumin (BSA) is found for [Pt-BFZ], which is the least internalized inside the cells. All the complexes are able to covalently interact with DNA. The most cytotoxic complexes, [Pt-MeIm] and [Pt-BFZ] induce cellular accumulation in G0/G1 and apoptosis by a similar pathway, probably involving a reactive oxygen species (ROS) generation mechanism. [Pt-BFZ] turns out to be the most efficient complex regarding ROS generation and causes mitochondrial membrane depolarization, whereas [Pt-MeIm] induces the opposite effect, hyperpolarization of the mitochondrial membrane. On the contrary, the least cytotoxic complex, [Pt-CTZ] cannot block the cell cycle or generate ROS and the mechanism by which it induces apoptosis could be a different one.

Digoxin – a therapeutic agent and mechanistic probe: review of liquid chromatographic mass spectrometric methods and recent nuances in the clinical pharmacology attributes of digoxin

Digoxin is an important therapeutic agent for the treatment of congestive cardiac failure. In spite of its narrow therapeutic index, digoxin has been used extensively by the medical community and, lately, the use of digoxin as a mechanistic probe for p-glycoprotein transporter activity has increased. This review describes recent trends in the bioanalysis of digoxin, where scores of liquid chromatographic–mass spectrometric assays have been successfully employed to measure digoxin in preclinical, clinical and mechanistic studies. It provides various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions, for example, to enable the development of sound bioanalytical methods for digoxin. Some recent updates with regard to clinical pharmacology, absorption and disposition aspects of digoxin have been included. Overall, liquid chromatographic–mass spectrometric assays represent an important tool for many future preclinical, clinical and mechanistic probe studies that would probe digoxin with or without other coadministered substrates.

Increased digitalis-like immunoreactive substances in neonatal plasma measured using fluorescence polarization immunoassay

OBJECTIVE

To better define the reported increased digitalis-like immunoreactive substances (DLIS) in neonatal plasma, we studied the relation among plasma DLIS level, blank intensity (BLK-I) value at FPIA measurement and plasma total bilirubin level.

METHODS

The DLIS levels were measured in 10 neonates with or without jaundice and 10 infants in good health, using fluorescence polarization immunoassay (FPIA) and microparticle enzyme immunoassay (MEIA). BLK-I value and plasma total bilirubin level were also measured simultaneously.

RESULTS

In neonates with jaundice, DLIS using FPIA, BLK-I and total bilirubin level were 0.58 +/-0.13 ng/mL, 2598 +/- 408, and 17.98 +/- 1.13 mg/dL, respectively, before phototherapy, and 0.33 +/-0.06 ng/mL, 1886 +/- 237, and 15.16 +/- 2.07 mg/dL after phototherapy. Corresponding values in neonates without jaundice were (DLIS: 0.34 +/-0.04 ng/mL; BLK-I: 1,764 +/- 278; total bilirubin: 10.37 +/- 4.54 mg/dL); in healthy infants (0.12 +/-0.06 ng/mL, 400.7 +/- 4.6 and 0.42 +/- 0.13 mg/dL, respectively) and in healthy volunteers (0.10 +/-0.07 ng/mL, 403.1 +/- 8.4, and 0.58 +/- 0.30 mg/dL, respectively). Using MEIA, DLIS was not detected in 10 neonates, 10 infants and 20 healthy volunteers.

CONCLUSIONS

A fluorescent compound related to bilirubin increased the BLK-I value in the measurement of neonatal plasma using FPIA. The fluorescence was not the result of endogenous digitalis-like factors.

Digitalis-like immunoreactive substances in maternal and umbilical cord plasma: a comparative sensitivity study of fluorescence polarization immunoassay and microparticle enzyme immunoassay

Digitalis-like immunoreactive substances (DLIS) obtained from maternal and umbilical cord plasma at delivery were measured by fluorescence polarization immunoassay (FPIA; TDX, Abbott) and microparticle enzyme immunoassay (MEIA; IMX, Abbott). In each sample, concentrations of dehydroepiandrosterone, dehydroepiandrosterone sulfate, estradiol, estriol, hydrocortisone, progesterone, and testosterone were measured by radioimmunoassay, and cross-reaction tests of DLIS with these substances were conducted. By FPIA, the concentration of DLIS in umbilical cord plasma (0.55 +/- 0.22 ng/mL) was significantly higher than that in maternal plasma (0.23 +/- 0.11 ng/mL). In the cross-reaction tests, when the concentration of dehydroepiandrosterone sulfate was higher than 1.0 microg/mL or that of progesterone was higher than 0.5 microg/mL, DLIS were detected by FPIA. However, DLIS were not found either in the samples or in the cross-reaction tests by MEIA. By radioimmunoassay, there was no significant difference in the dehydroepiandrosterone sulfate concentration between the maternal plasma (2,917 +/- 1,001 ng/mL) and the umbilical cord plasma (1,957 +/- 376 ng/mL). The progesterone concentration in the umbilical cord plasma (310.0 +/- 85.7 ng/mL) was significantly higher than that in the maternal plasma (126.4 +/- 38.5 ng/mL). These results suggest that dehydroepiandrosterone sulfate in maternal plasma and progesterone in maternal and umbilical cord plasma may be measured as digoxin by FPIA.

Digoxin Assays: Frequent, Substantial, and Potentially Dangerous Interference by Spironolactone, Canrenone, and Other Steroids

Background: A case of digoxin toxicity resulted from falsely low values with the MEIA II assay for digoxin (AxSYM®; Abbott). The low results were caused by negative interference from canrenone and spironolactone, the latter of which has recently been advocated for the treatment of severe heart failure. Analytical interference from spironolactone has been reported, but little information is available for this effect with newer digoxin assays.

Methods: We examined nine assays (AxSYM, IMx®, TDx®, Emit®, Dimension®, aca®, TinaQuant®, Elecsys®, and Vitros®) for interference by spironolactone, canrenone, and three metabolites. Additionally, all routine digoxin measurements (AxSYM) over a period of 16.5 months (n = 3089) were monitored for interference.

Results: Suppression of the expected values by canrenone (3125 μg/L) was observed for the AxSYM (42% of expected value), IMx (51%), and Dimension (78%) assays. A positive bias was observed for the aca (0.7 μg/L), the TDx (0.62 μg/L), and the Elecsys (>0.58 μg/L). Twenty-five of 669 routinely monitored patients had falsely low results. Nineteen of these had potentially toxic concentrations of digoxin (Emit; >2.0 μg/L), although the AxSYM assay indicated therapeutic or less severe toxic concentrations (Δmax = 7.1 μg/L). Except for two unresolved cases, this was attributable to spironolactone, canrenone, hydrocortisone, or prednisolone. Standard doses of spironolactone (up to 50 mg/day) in patients with heart failure displayed inhibition <11%.

Conclusions: The frequency and magnitude of the false-negative results particularly compromise the use of both microparticle enzyme immunoassays. Not only may toxic concentrations remain unidentified, but intoxication could occur should dosage be increased because of falsely low results. With 11 million digoxin tests/year ordered in the US, conceivably many patients could be adversely affected.

Predictive performance study of two digoxin assays in subjects with various degrees of renal function

This prospective study was conducted to compare the predictive performance of fluorescence polarization immunoassay (FPIA, Abbott TDx Digoxin II) and radioimmunoassay (RIA, Kallestad Labs) with combined low-pressure liquid chromatography/RIA (LPLC/RIA) digoxin assay in measuring 15-17 serum digoxin concentrations (SDC) obtained after a single 10 microg/kg intravenous digoxin dose in patients with various degrees of renal function and at different SDC ranges. Eighteen men and women were stratified into 3 age- and gender-matched groups based upon renal function [N = 6 in each, group I (Cl(cr) < 10 mL/min), group II (Cl(cr) = 10-50 mL/min), and group III (Cl(cr) > 50 mL/min)]. Serum digoxin concentrations were measured at time zero; at 0.25, 0.5, 0.75, 1, 2, 3, 4, 6, 8, and 12 hours; and at 2, 3, 4, and 5-7 days after the digoxin dose, using the three different digoxin assays. TDx Digoxin II was unbiased [mean error -0.09 (95% CI -0.19, 0.01)] and RIA biased [mean error -0.29 (95% CI -0.36, -0.21)] to over-predict SDC by 14.2%. In group I patients, the analysis revealed a bias to over-predict SDC by 6.0% for TDx Digoxin II [mean error -0.16 (95% CI -0.29, -0.07)] and an unbiased performance by RIA. In groups II and III, both TDx Digoxin II and RIA showed biased performance, the mean magnitude of bias was low (< 20%). For intermediate SDC range (> 0.5 ng/mL and < or = 3.0 ng/mL), TDx Digoxin II was unbiased in predicting SDC, whereas RIA was biased to under-predict SDC [mean error 0.13 (95% CI 0.10, 0.16)] by 9.9%. The magnitude of bias observed in all cases was less than 20%. Both assays, TDx Digoxin II and RIA, imprecisely measured SDC for all samples combined, different groups and SDC ranges. In all time-paired samples, TDx Digoxin II (FPIA) performed better than the RIA. In conclusion, the magnitude of bias observed with either assay at different groups and SDC ranges was not likely to be clinically relevant. Therefore, either assay may be used to measure SDC in clinical practice.

Analytical performance of a monoclonal digoxin assay by dry chemistry on the Vitros 950

Digoxin assay in plasma/serum samples is used for therapeutic measurements as a guide to clinical management of cardiac patients. A thin dry film multilayer monoclonal immunoassay for digoxin, Vitros, was evaluated for analytical performance. The effect of digoxin-like immunoreactive substances (DLIS) was studied assaying plasma samples taken from 100 renal disease patients, 62 hepatic disease patients and 40 pregnant women not receiving digoxin. The Vitros digoxin assay was compared with the AxSym digoxin II assay using plasma samples from 180 patients treated with digoxin. The results revealed satisfactory precision and accuracy for therapeutic drug monitoring purposes: the coefficient of variation (CV%) was lower than 5%; results for dilutions were linear in the range 0.4-3.9 microlg/L and mean analytical recovery was 105%. Measurable DLIS concentrations were observed in 29% of hepatic disease patients and in 7% of renal disease patients with apparent digoxin concentration ranging from 0.4 to 0.75 microg/L. The incidence of DLIS was comparable to that observed with AxSym digoxin II. Comparative results from patient samples gave a regression line equation: Yvitros 950=0.96XAxym +0.14, r=0.89. The data revealed a mean difference of 0.09+/-0.26 microg/L significantly greater than zero (p=0.02). We concluded that Vitros digoxin assay for precision, accuracy and extent of DLIS interference may be a good method for therapeutic drug monitoring; care needs to be taken since assay results generated by Vitros and AxSym analysers are not necessarily interchangeable.

Validity of unbound digoxin measurements by immunoassays in presence of antidote (Digibind)

Measurement of unbound digoxin in presence of Fab fragments may be useful in management of overdoses. The analysis can be performed on serum directly or on ultrafiltrate of serum. The architecture of the immunoassay may influence the validity of results obtained using these two approaches. We tested this hypothesis by preparing serum mixtures containing various concentrations of digoxin and Digibind and analyzed them by the immunoassays before and after ultrafiltration. Four samples collected from Digibind-treated patients were also analyzed before and after ultrafiltration. The slopes and the y-intercepts of the measured versus the expected values for serum and its ultrafiltrate overlapped for the MEIA digoxin assay. For other three immunoassays tested (ACS:180, Stratus, and On-Line), either the slope or the intercept for measured versus the expected results for serum were significantly different (P < 0.05) than those for ultrafiltrate. Following addition of digoxin and Digibind, differences in results for serum analyzed directly or after ultrafiltration were < 0.50 ng/ml. Comparable samples from digoxin-overdosed patients treated with Digibind had differences of > 1.0 ng/ml. Previous claims reporting direct analysis of digoxin in presence of antidote but not having used patient samples for validation should be revisited. To date, analysis of serum ultrafiltrate by an immunoassay proven not to have matrix bias remains the most accurate approach in measuring unbound digoxin in presence of antidote.

Analytic performance of two automated nonpretreatment digoxin immunoassays

The analytic performance of two automated nonpretreatment digoxin methods, AxSYM Digoxin II and Vitros digoxin immunoassays, was assessed. Both assays had analytic sensitivities of less than 0.2 microg/L, were linear from digoxin concentrations of 0.5 to 4.0 microg/L, and showed acceptable precision, with a maximum total coefficient of variation (CV) of 8.9% and 6.4% for the AxSYM and Vitros, respectively. Comparison of the two methods using samples from patients receiving digoxin gave the following relationship: Vitros = 0.91 x AxSYM + 0.23 (r = 0.97, Sy,x = 0.12). Digoxinlike immunoreactive factor (DLIF) crossreactivity was examined in specimens from patients who had hepatic disease, renal insufficiency, had undergone cardiac surgery, and in neonatal cord blood samples. Minimal crossreactivity was observed for most samples and the average crossreactivity for each group of samples was comparable for the two methods. The recovery of digoxin added to samples from each group of DLIF was similar, except for that from cord blood samples, for which recovery was significantly lower with the AxSYM method. Titration of a digoxin-spiked serum pool with digoxin-immune Fab showed a similar decrease in the measured digoxin concentration for both methods. Overall, the analytic performance characteristics of these two methods were comparable.