The measurement of digitoxin in human serum by radioimmunoassay

A thermoresponsive biodegradable polymer with intrinsic antioxidant properties

Oxidative stress in tissue can contribute to chronic inflammation that impairs wound healing and the efficacy of cell-based therapies and medical devices. We describe the synthesis and characterization of a biodegradable, thermoresponsive gel with intrinsic antioxidant properties suitable for the delivery of therapeutics. Citric acid, poly(ethylene glycol) (PEG), and poly-N-isopropylacrylamide (PNIPAAm) were copolymerized by sequential polycondensation and radical polymerization to produce poly(polyethylene glycol citrate-co-N-isopropylacrylamide) (PPCN). PPCN was chemically characterized, and the thermoresponsive behavior, antioxidant properties, morphology, potential for protein and cell delivery, and tissue compatibility in vivo were evaluated. The PPCN gel has a lower critical solution temperature (LCST) of 26 °C and exhibits intrinsic antioxidant properties based on its ability to scavenge free radicals, chelate metal ions, and inhibit lipid peroxidation. PPCN displays a hierarchical architecture of micropores and nanofibers, and contrary to typical thermoresponsive polymers, such as PNIPAAm, PPCN gel maintains its volume upon formation. PPCN efficiently entrapped and slowly released the chemokine SDF-1α and supported the viability and proliferation of vascular cells. Subcutaneous injections in rats showed that PPCN gels are resorbed over time and new connective tissue formation takes place without signs of significant inflammation. Ultimately, this intrinsically antioxidant, biodegradable, thermoresponsive gel could potentially be used as an injectable biomaterial for applications where oxidative stress in tissue is a concern.

Advanced nanocomposites for bone regeneration

The field of orthopedic tissue engineering is quickly expanding with the development of novel materials and strategies designed for rapid bone regeneration. While autologous bone grafts continue to be the standard of care, drawbacks include donor-site morbidity and short tissue supplies. Herein we report a novel nanocomposite sponge composed of poly(1,8-octanediol-co-citrate) (POC) and the bioactive ceramic β-tricalcium phosphate (TCP). We show that these nanocomposite sponges can be used as a depot for bone-producing (a.k.a. osteogenic) growth factors. In vitro bioactivity is demonstrated by significant upregulation of osteogenic genes, osteopontin (∼3 fold increase), osteocalcin (∼22 fold increase), alkaline phosphatase (∼10 fold increase), and transcription factor, RUNX2 (∼5 fold increase) over basal expression levels in mesenchymal stem cells. In vivo osteogenicity and biocompatibility is demonstrated in a standard subcutaneous implant model in rat. Results show that the nanocomposite sponge supports complete cell infiltration, minimal adverse foreign body response, positive cellular proliferation, and cellular expression of osteogenic markers in subcutaneous tissue. The results shown herein are encouraging and support the use of this sponge for future bone tissue engineering efforts.

Properties of Novel Anti-digoxin Antisera in Radioimmunoassay Using Homologous and Site Heterologous Tritium-Labeled Antigens Involving a [3H]-Leucine Moiety

The specificities of antisera against digoxin C-3' or C-3'' hemisuccinate-bovine serum albumin (BSA) conjugate were assessed by cross-reactivity studies with digoxin metabolites by radioimmunoassay (RIA) using the homologous and the site heterologous tritium-labeled antigens. One of the tracers used was digoxin 3'-hemisuccinyl-[3H]-leucine; the other was digoxin 3''-hemisuccinyl-[3H]-leucine, which had been prepared from digoxin 3''-hemisuccinate. When the tracer with [3H]-leucine at the C-3' position was used, antisera (I-1, I-3) elicited by digoxin 3'-hemisuccinate-BSA conjugate showed the following cross-reactivity: digoxigenin bisdigitoxoside (0.34%, 76%), digoxigenin monodigitoxoside (0.11%, 65%), digoxigenin (0.02%, 26%) and dihydrodigoxin (9.4%, 1.2%). However, when using the homologous antigen, antiserum (I-1) was highly specific against the digitoxose chain. When the site heterologous antigen, digoxin 3''-hemisuccinyl-[3H]-leucine was combined, this antiserum showed high cross-reactivity to digoxin degradation products. This digoxin RIA using antiserum (I-1) with the homologous antigen measures unmetabolized digoxin. On the other hand, the RIA system using antiserum (I-3) with the homologous antigen had cross-reactivity with the metabolites in accordance with their relative cardio-activities, so this system would be useful in therapeutic drug monitoring of digoxin.

Measurement of beta-methyldigoxin level in serum from patients by enzyme immunoassay using novel specific antiserum with a phenyl boric acid column

The authors compared serum beta-methyldigoxin (MDx) levels in digitalized patients by enzyme immunoassay (EIA) using anti-MDx 3'-hemisuccinate BSA antiserum (antiserum-I) with commercial antidigoxin antiserum (antiserum-II). The usefulness of a phenyl boric acid (PBA) column for pretreatment of the serum samples was also investigated. The assay using antiserum-I demonstrated good accuracy and precision in the concentration range of 0.5 to 5 ng/mL. When the specificities of antiserum-I and antiserum-II were assessed by cross-reactivity studies with various related compounds, antiserum-I was much more specific for MDx antiserum-II. Using a phenyl boric acid (PBA) column, MDx, and digoxigenin, which exhibits a negligible cross-reactivity, were separated from serum, including MDx and its metabolites. The recovery tests of MDx using antiserum-I with a PBA column in human serum were satisfactory and no interference of metabolites of MDx was observed. Mean MDx concentrations in serum samples (n = 30) from digitalized patients by EIA using antiserum-I with PBA column, antiserum-I, and antiserum-II were 1.06, 1.30, and 1.74 ng/mL, respectively. These results indicate that our EIA system using antiserum-I with a PBA column for pretreatment of serum samples is useful to more precisely measure the unchanged type of MDx in patients.

Measurement of serum digitoxin in patients by radioimmunoassay using specific antiserum

INTRODUCTION

Digitoxin is used to treat patients with heart failure.

METHODS

A radioimmunoassay procedure for the specific determination for digitoxin in serum was developed using the antiserum (antiserum (A)) raised against digitoxin 3'-hemisuccinate-BSA conjugate.

RESULTS

The intra- and interassay variability were <10% in the range of 5-100 ng/ml. The specificities of antiserum (A) and the commercial anti-digitoxin antiserum (antiserum (B)) were assessed by cross-reactivity studies with various related compounds. Antiserum (A) was highly specific for digitoxin. Mean digitoxin concentrations in serum samples (n=34) from digitalized patients by RIA using these antisera were 10.0 and 12.4 ng/ml, respectively.

CONCLUSION

This RIA using antiserum (A) measure unmetabolized digitoxin and may be applicable for pharmacokinetic studies.

A radioimmunoassay for type I iodothyronine 5'-monodeiodinase in human tissues

We have developed a sensitive, specific and reproducible radioimmunoassay (RIA) for measurement of human type I monodeiodinase (5'-DI) protein. Anti-5'-DI antibody was produced by immunization of rabbits with a conjugate of bovine serum albumin and a 16 amino acid synthetic peptide, corresponding to a portion of the carboxy-terminal region of the human 5'-DI (PI-99). In a final dilution of 1:500, our anti-5'-DI antibody bound about 30%-35% of a tracer amount of 125I-PI-99. The detection threshold of the RIA approximated 0.4 pmol PI-99 or an equivalent amount of 0.4 pmol 5'-DI. The coefficient of variation averaged 5% within an assay and 14% between assays. Dose-response curves of tissue proteins were essentially parallel to that of PI-99. In a total number of 35 normal human tissue samples, the mean (+/- standard deviation [SD], picomole per milligram of protein [pmol]) 5'-DI content was 25 +/- 6.7 in kidney, it was significantly lower (p < 0.05) in liver at 3.9 +/- 1.1, 2.8 +/- 0.8 in intestine, 2.3 +/- 0.98 in adrenal, 4.2 +/- 2.5 in skeletal muscle, 3.8 +/- 1.4 in heart and 2.6 +/- 2.4 in thyroid; it was 1.4 +/- 0.3 in Graves' thyroid. Our data suggest that (1) 5'-DI is distributed widely among human tissues; (2) kidney is the tissue most enriched with 5'-DI; (3) 5'-DI content in the thyroid is not increased in Graves' disease.

Digitoxin and its metabolites in patients with liver cirrhosis

Pharmacokinetic profile and urinary excretion of digitoxin and 4 metabolites were investigated in 9 patients with biopsy confirmed liver cirrhosis (median antipyrine clearance 20.0 +/- 5.4 ml/min; X +/- SEM) and were compared with that of 8 healthy volunteers (antipyrine clearance 36.9 +/- 4.9 ml/min) following intravenous and p.o. administration of 1 mg digitoxin. The kinetic parameters derived from the digotoxin plasma concentration time curve and from urinary recovery including total clearance of unchanged digitoxin did not differ significantly between both groups investigated. Renal clearance of digitoxin was 0.017 +/- 0.005 ml/min/kg in the patient group and 0.011 +/- 0.002 ml/min/kg in the volunteers (NS); it was 0.00340 +/- 0.00047 ml/min/kg and 0.00223 +/- 0.00039 ml/min/kg, respectively for digitoxigenin-bis-digitoxoside (NS), 0.00006 +/- 0.00001 ml/min/kg and 0.00016 +/- 0.00005 ml/min/kg for digitoxigenin-mono-digitoxoside (P < 0.05), 0.00041 +/- 0.00013 ml/min/kg and 0.00088 +/- 0.00032 ml/min/kg for digitoxigenin (P < 0.05), 0.00135 +/- 0.00049 ml/min/kg and 0.00113 +/- 0.00042 ml/min/kg for digoxin (NS). In conclusion, hydrolysis of digitoxin is altered in liver cirrhosis, whereby a significant reduction in the renal clearance and urinary recovery of digitoxigenin-mono-digitoxoside and digitoxigenin was seen in the present study.

Detection of hepatitis B virus DNA in human serum samples: use of digoxigenin-labeled oligonucleotides as modified primers for the polymerase chain reaction

Nonradioactive techniques have been used for the direct detection of hepatitis B virus DNA in human serum samples. A comparison of two different systems using digoxigenin-labeled DNA probes is presented. Furthermore, oligonucleotides containing one molecule of the hapten digoxigenin at the 5'-end were prepared and used as primers for the polymerase chain reaction. Amplified DNA can be directly analyzed with anti-digoxigenin Fab fragments labeled with alkaline phosphatase and chemiluminescent substrates.

Reversible activation of soluble guanylate cyclase by oxidizing agents

Soluble guanylate cyclase of human platelets was stimulated by thiol oxidizing compounds like diamide and the reactive disulfide 4, 4'-dithiodipyridine. Activation followed a bell-shaped curve, revealing somewhat different optimum concentrations for each compound, although in both cases, higher concentrations were inhibitory. Diamide at a concentration of 100 microM transiently activated the enzyme. In the presence of moderate concentrations of diamide and 4,4'-dithiodipyridine, causing a two- to fourfold activation by themselves, the stimulatory activity of NO-releasing compounds like sodium nitroprusside was potentiated. In contrast, higher concentrations of thiol oxidizing compounds inhibited the NO-stimulated activation of soluble guanylate cyclase. Activation of guanylate cyclase was accompanied by a reduction in reduced glutathione and a concomitant formation of protein-bound glutathione (protein-SSG). Both compounds showed an activating potency as long as reduced glutathione remained, leading to inhibition of the enzyme just when all reduced glutathione was oxidized. Activation was reversible while reduced glutathione recovered and protein-SSG disappeared. We propose that diamide or reactive disulfides and other thiol oxidizing compounds inducing thiol-disulfide exchange activate soluble guanylate cyclase. In this respect partial oxidation is associated with enzyme activation, whereas massive oxidation results in loss of enzymatic activity. Physiologically, partial disulfide formation may amplify the signal toward NO as the endogenous activator of soluble guanylate cyclase.

Non-radioactive labeling and detection of nucleic acids. IV. Synthesis and properties of digoxigenin-modified 2'-deoxyuridine-5'-triphosphates and a photoactivatable analog of digoxigenin (photodigoxigenin)

The chemical syntheses of novel digoxigenin-derivatized compounds are described which are modified substrates for enzymatically or photochemically non-radioactive digoxigenin labeling of nucleic acids. Various activated digoxigenin-haptens are coupled to 5-aminoallyl-substituted 2'-deoxyuridine-5'-triphosphate. This results in digoxigenin-modified nucleoside triphosphates of variable spacer lengths (Dig-[4]-dUTP/Dig-[11]-dUTP/Dig-[16]-dUTP) which can be used as substrates for enzymatic labeling of DNA with digoxigenin-haptens by Klenow enzyme-catalysed random-primed synthesis. In addition the synthesis of N-[4-azidobenzoyl]-N'-[(3-O-digoxigeninyl)methylcarbonyl)]-1 ,8-diamino- 3,6-dioxaoctane (photodigoxigenin), a photoactivatable analog of digoxigenin, is described which can be applied for photolabeling of DNA and RNA with digoxigenin-haptens leaving the nucleic acid molecules intact.

Effects of active immunization against L-triiodothyronine on serum thyrotropin levels and liver mitochondrial alpha-glycerophosphate dehydrogenase activity in rats: evidence for reduced hormone disposal to cells

Thyroid hormone binding autoantibodies have been observed in serum from patients affected by either thyroid disorders or autoimmune nonthyroid diseases. In most instances, no major involvement of thyroid status of these patients has been reported. However, some authors have attributed the occurrence of hypothyroidism to high capacity thyroid hormone binding autoantibodies. In order to verify such a hypothesis, the effect of these autoantibodies on serum TSH and liver mitochondrial alpha-glycerophosphate dehydrogenase has been investigated in rats, wherein circulating T3-binding antibodies (max cap 10(-12) 10(-8) to mol/l) were induced by active immunization. Starting from the 3rd week after antigen injection, the binding of 125I-T3 to serum immunoglobulins was progressively increased, with a peak at the 5th week. In immunized animals considered as a whole group, serum TSH levels were significantly higher and liver mitochondrial alpha-glycerophosphate dehydrogenase activity was significantly lower than in normal rats (m +/- SE: 145 +/- 15 vs 34 +/- 2 ng/dl and 0.0450 +/- 008 vs 0.0980 +/- 005 delta A. mg/prot/.min, respectively; p less than 0.001). The pattern of both TSH increase and alpha-glycerophosphate dehydrogenase decrease were similar to the evolution of 125-I-T3 binding to serum immunoglobulins, the maximal TSH values and lowest enzyme levels being observed at the 5th week after the beginning of the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific binding characteristics of high affinity monoclonal antidigitoxin antibodies

The specificity of various monoclonal antidigitoxin antibodies was characterized using 6 cardiac glycoside analogs. Spleen cells from BALB/c mice, immunized with BSA- or KLH-digitoxin conjugates, were fused with NS1 myeloma cells, and antibody-producing hybrids were identified by radioimmunoassay. Twenty-one monoclonal antidigitoxin-specific antibodies were obtained, 10 of which were cloned and characterized for affinity and specificity. All the antibodies had a high affinity constant, ranging from 8.10(8) to 2.5.10(10) 1/M. On the basis of their binding specificities, the antibodies could be classified into 3 groups: the first contained 7 antibodies exhibiting high cross reactivity (42-100%) with digitoxigenin, whereas the second and third groups did not recognize this analog (cross-reactivity of 1%). In the former group, the absence of the sugar moiety only slightly affected the binding reaction, although for the two other groups, this structure did appear to be involved in antibody recognition. Changes in the functional groups of the hapten molecule led to considerable changes in the antibody-antigen reaction. For all the antibodies except one, saturation of the lactone ring considerably affected binding. These results demonstrated that monoclonal antibodies of different specificities with respect to both the steroid backbone and the sugar moiety of digitoxin can be induced using a digitoxin-protein conjugate.

Development of a radioimmunoassay for triiodothyronine sulfate

This paper is the first description of a radioimmunoassay (RIA) for triiodothyronine sulfate (T3S). Rabbits were immunized against T3S coupled to bovine serum albumin using carbodiimide. All animals produced antibodies to T3S but also even higher titers of T3 antibodies. Ka values for binding of T3 and T3S to these antisera varied between 2 x 10(10) and 8 x 10(10) M-1. One of the antisera (#8193) was selected for use in the T3S RIA because of a high titer of T3S antibodies (final dilution 1:50,000), a high sensitivity to T3S (less than 2.5 fmol/tube), and a low crossreactivity by T3 (0.4%). This RIA provides a tool for the study of the importance of sulfation as a metabolic pathway for T3.

Simultaneous analysis of digitoxin and its clinically relevant metabolites using high-performance liquid chromatography and radioimmunoassay

A specific assay for determining the urinary excretion of unchanged digitoxin and its metabolites is described. The procedure includes solvent extraction of urine at pH 8.5, reversed-phase high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) of equivalent fractions. Confidence limits showed good linearity and precision of recovery and high sensitivity, accuracy and specificity. Cross-reactivities were high for digitoxigenin (DGTN) and digitoxigenin bisdigitoxoside (Bis-DGTN), they were low for digitoxigenin monodigitoxoside (Mono-DGTN) or digoxin when [125I]digitoxin RIA was used. The interference of endogenous compounds in urine in the RIA was overcome by using HPLC. Compared with results reported in the literature, the urinary recovery of unchanged digitoxin was lower, being only 8.11 +/- 1.51% of the dose administered. Amounts of 6.52 +/- 1.31% were excreted hydrolysed as Bis-DGTN, Mono-DGTN, DGTN or C12-hydroxylated as digoxin.

Pharmacokinetic interactions between digoxin and other drugs

Drug interactions with digoxin are important because of this agent's narrow therapeutic index. Among the drugs that can decrease digoxin bioavailability are cholestyramine, antacid gels, kaolin-pectate, certain antimicrobial drugs and cancer chemotherapeutic agents. In selected patients, antibiotics may enhance digoxin bioavailability by eliminating intestinal flora that metabolize digoxin. Antiarrhythmic drugs, such as quinidine and amiodarone, can markedly increase steady state serum digoxin levels. Certain calcium channel blocking drugs, particularly verapamil, have a similar effect. Potassium-sparing diuretic drugs, such as spironolactone, can alter digoxin pharmacokinetics. Indomethacin may decrease renal excretion of digoxin in preterm infants. Finally, rifampin, an antibiotic used in the treatment of tuberculosis, may lower steady state serum digoxin levels in patients with severe renal disease. Physicians must maintain constant vigilance whenever medications are added to or withdrawn from a therapeutic regimen that includes digoxin.

A comparative study between animals and monoclonal anti-digitoxin antibodies

Anti-digitoxin antibodies have been produced by immunizing rabbits and by monoclonal techniques using the same digitoxin-protein conjugate. Titres, inhibition curves, affinities, dissociation and association rate-constants have been investigated for the two antibodies. It appears that the animal immune serum gives better criteria (except specificity) than the monoclonal ones. However, both can be used for quantitative assays, with less sensitivity for the monoclonal antibody. The main advantage of monoclonal production is to conduct large amounts of specific immunoglobulins which are very useful for human administration after a digitalis overdose.

Comparative electrophysiologic effects of digoxin in the nonsedated chronically instrumented puppy

The electrophysiologic effects of acute but not chronic administration of cardiac glycosides have been studied. Nineteen chronically instrumented beagle puppies underwent 2-week courses of parenteral digoxin in three dosage regimens: six received digoxin, 0.04 mg/kg/day; seven received 0.03 mg/kg/day; and 11 received 0.02 mg/kg/day. Mean serum concentrations were 3.2 ng/ml, 1.3 ng/ml, and 1.0 ng/ml, respectively. Significant electrophysiologic effects on sinus node function were produced only by the highest dose. Atrioventricular node conduction was significantly delayed among animals receiving both high and middle dosages. All three regimens significantly effected atrioventricular specialized conduction system functional refractory periods. Atropine decreased digoxin-induced effects on all measured parameters but totally eliminated the digoxin effect on the corrected sinus node recovery time.

Involvement of endogenous digitalis-like substance in genesis of deoxycorticosterone-salt hypertension

In an attempt to evaluate the role of endogenous digitalis-like substance in the genesis of deoxycorticosterone (DOCA) -salt hypertension, the effects of intravenous anti-digoxin antibody on the blood pressure response were observed in male Wistar rats that underwent heminephrectomy followed by treatment with DOCA and saline. Administration of anti-digoxin antibody caused a marked decrease in the blood pressure which continued for about an hour. Such a change in the blood pressure was not observed in pertinent control animals. Thus, it seems that endogenous digitalis-like substance plays an important role in the genesis of DOCA-salt hypertension.

Fluoroimmunoassay of digoxin in serum

A heterogeneous (solid-phase separation) fluoroimmunoassay for digoxin in serum was developed employing antibodies coupled to magnetisable cellulose/iron oxide particles and a fluorescein-labelled digoxin derivative as tracer. Intrinsic fluorophores and other potentially interfering components of serum samples were reliably and completely removed at the separation and wash steps of the assay procedure which were facilitated by magnetic sedimentation. In order to attain adequate sensitivity (detection limit 0.2 micrograms/l (0.26 nmol/l) serum digoxin), a sample volume of 500 microliters was necessary. Assay results for patients' specimens correlated well with those obtained using established charcoal--separation (r = 0.96) and magnetisable solid-phase (r = 0.95) radioimmunoassays. The feasibility of a "stat" adaptation of the fluoroimmunoassay that involved only two standards (0.5 and 4 micrograms/l digoxin) was demonstrated. The stat method would be suitable for the assay of urgent or single specimens.

Radioimmunoassay of carteolol in human plasma

A radioimmunoassay for the direct measurement of carteolol, a new beta-adrenoreceptor blocker, in human plasma was developed. Carteolol was acylated to form O-glutarylcarteolol, which was conjugated to bovine serum albumin to provide the immunogen. Antibody to carteolol was raised in New Zealand albino rabbits. The tracer was the radioiodinated derivative of O-glutarylcarteolol-tyrosine methyl ester conjugate. The method is highly sensitive, with a lower quantifiable concentration of approximately 0.4 ng of carteolol/ml using 0.1 ml of plasma, and has good specificity, with the major metabolite (8-hydroxycarteolol) showing only 0.2% cross-reactivity. It is reproducible, with relative standard deviations from triplicate standard curves being mostly within +/- 8%. The method is currently being used to monitor carteolol levels in clinical samples.

Determination of triiodothyronine in serum by enzyme- and radioimmunoassay: a comparative study

An evaluation of a heterogeneous enzyme immunoassay for determination of triiodothyronine in serum (Enzymun-Test T3, Boehringer Mannheim) is presented. The enzyme immunoassay was compared with the laboratory routine radioimmunoassay. The precision of both assays was satisfactory at triiodothyronine concentrations between 1.0 and 8.0 nmol/l (coefficients of variation from day to day less than or equal to 10%). Average recoveries of triiodothyronine in pool sera ranged with the Enzymun-Test T3 from 96--104% and with the radioimmunoassay from 88--111%. A comparison of the results obtained by Enzymun-Test T3 and the radioimmunoassay in a series of 103 patients showed a good correlation between both methods. L-thyroxine did not cause a relevant cross-reaction in the enzyme immunoassay. About 20 unknown samples can be analyzed in triplicate by Enzymun-Test T3 within 260 minutes.

A standard approach to compiling clinical pharmacokinetic data

A standard format for a Clinical Pharmacokinetic Summary is proposed. It consists of a heading, tables, notes, and references for each drug reviewed. The table presents a unified and logical set of clinically useful population pharmacokinetic parameters. They concern four major areas: absorption, distribution, elimination, and the relationship of concentration to effect. Within each major group, parameters dealing with extents and rates of processes are given. Each such parameter is really two: a population mea value (for example, average volume of distribution) and the standard deviation of individual values about this mean. The first value allows individual predictions of dosage or drug level to be made; the second allows computation of the likely proximity of subsequently observed quantities to those predictions. The table presents single consensus values for each population parameter, rather than a list of values. A procedure for computing these consensus values, and for revising them in the light of new data, or reinterpreted old data, is given. Examples of Summaries are given. The method appears applicable to a variety of drugs. We suggest our approach as a standard one for preparing Clinical Pharmacokinetic Summaries, and urge our colleagues to consider it for that purpose.

Interindividual differences in the pharmacokinetics of digitoxin and digoxin during long-term treatment

Patients suffering from congestive heart failure received maintenance doses of digitoxin (N = 10) or digoxin (N = 8). The plasma glycoside concentration was determined, and after a single dose of 3H-digitoxin or 3H-digoxin, the decline and excretion of radioactivity were measured over a period of 7 (digitoxin) and 3 days (digoxin). Plasma radioactivity declined with a T1/2 beta between 77 and 234 h (mean 138 h) in the case of digitoxin and with a T1/2 beta between 9.2 and 38.6 h (mean 23.5 h) for digoxin. A close correlation between T1/2 beta and excreted radioactivity and T1/2 beta and total plasma level was found for digitoxin. In 4 patients TLC of urine showed that interindividual variations in digitoxin elimination could possibly be attributed to variation in metabolism, resulting in the production of different metabolites. Predicted digitoxin plasma levels agreed well with measured values. The maintenance dose could be calculated from the total body clearance (VCl) and a presumed plasma glycoside level. The recommended technique facilitates dosage calculations in patients treated with digitoxin.

Quantification of digoxin by enzyme immunoassay: synthesis of a maleimide derivative of digoxigenin succinate for enzyme coupling

We synthesized the m-maleimidobenzoyl derivative of digoxigenin-3-0-succinate (through a p-phenylenediamine bridge) as a hapten derivative directed towards coupling to sulfhydryl grouos of beta-galactosidase. Prepared enzyme conjugate had about 97% of the enzyme labeled with the hapten derivative while retaining full enzyme activity. The enzyme immunoassay for digoxin we prepared showed a maximum sensitivity of 30 pg per assay (c.v. = 3%) with minimal cross-reaction with digotoxin (3.8%). Our method for hapten conjugation to beta-galactosidase is highly efficient and is simple and easily replicated.

Automated radioimmunoassay of nicotine

We have developed an automated nonequilibrium procedure for the radioimmunoassay of nicotine. The use of a unique iodinated nicotine derivative in this procedure gave a sensitivity of 10 micrograms/l for nicotine with a between-run precision of 7.4% and within-run precision of 6.0%. Nicotine levels of 60 to 67 micrograms/ml were found in subjects 15 min after smoking one standard cigarette. The technique herein reported is a very rapid, and sensitive radioimmunoassay for nicotine and facilitates the determination of nicotine in smoking subjects during the actual process of smoking.

Evaluation of enzyme immunoassays for determination of thyroxine (EMIT, ENZYMUN) and of thyroxine binding index

An evaluation of enzyme immunoassays for determination of thyroxine in serum (EMIT ABA thyroxine assay, Syva Corp., ENZYMUN assay thyroxine, Boehringer Mannheim) and of thyroxine binding index (ENZYMUN assay TBI1), Boehringer Mannheim) is presented. The precision of the enzyme immunoassays was adequate (coefficients of variation ranged from day to day with EMIT from 3--11% and with ENZYMUN from 4--11%). Both assays are specific and easy to perform. About 20 unknown samples can be analyzed in duplicate by EMIT within 60 minutes and by ENZYMUN within 250 minutes. A comparison of the results obtained by enzyme immunoassays and radioimmunoassay in a series of about 100 patients showed a good correlation between both methods. The precision of the ENZYMUN TBI assay was adequate (coefficient of variation from day to day 4.9%) and the thyroxine/TBI-ratio correlated well with the thyroxine/TBG-ratio.