Abbott TDx, Dade Stratus, and Du Pont aca automated digoxin immunoassays compared with a reference radioimmunoassay method.

Automated digoxin immunoassays with the Abbott TDx, Dade Stratus, and Du Pont aca were evaluated against an RIA similar to the Centers for Disease Control Candidate Reference Method. All three automated methods correlated poorly with the reference method. Particularly disconcerting were the falsely increased values (up to 0.6 micrograms/L) obtained by the Stratus for blank specimens. We discuss the inaccuracies of the results in terms of sample matrix effects, calibrator problems, lot-to-lot reagent variation, and our laboratory requirements. We strongly support the acceptance of the CDC Candidate Reference Method for digoxin and the establishment of a standardized protocol for determining the accuracy of digoxin measurements.

Limits of detection and quantification, as applied to an assay for digoxin.

The low-range sensitivity of a drug assay in routine use is an important aspect of that assay's clinical usefulness. We define three concepts for determining low range sensitivity: LC, the detection threshold; LD, the lower limit of "virtually ensured" detection; and LQ, the limit of quantitative determination. To illustrate these concepts, we apply them to a radioimmunoassay for digoxin, and show that for standards ranging from 0.3 to 5.0 micrograms/L, the LQ is 0.35 micrograms/L (+/- 10%).

Plasma platinum levels: relationship to cisplatin dose and nephrotoxicity.

Renal dysfunction is the dose-limiting toxic effect for many patients receiving cisplatin (CP). Despite hydration and/or forced diuresis, some patients develop nephrotoxicity, and patients at risk cannot be easily identified. We studied 77 patients with several types of carcinoma who received 115 cycles of CP, by 24-hour infusion, at doses of 40-100 mg/m2. Blood samples for platinum (Pt) analysis were obtained during and after CP infusion; plasma Pt levels were dose- and time-dependent. A significant rise in serum creatinine was seen after the first cycle and cumulatively over subsequent CP cycles. The largest subgroup of patients, those who received 80 mg/m2, was analyzed for predictors of nephrotoxicity. Twenty-five percent of patients exhibited nephrotoxicity (greater than 30% rise in serum creatinine or greater than 30% fall in creatinine clearance). These nephrotoxic patients had significantly higher plasma Pt levels during CP infusion than did nonnephrotoxic patients. Age, sex, cycle number, and pretreatment creatinine did not predict nephrotoxicity. Patients predisposed to nephrotoxicity with CP chemotherapy may be identifiable, on the basis of elevated plasma Pt, early in the course of CP infusion.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite.

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin. After affinity chromatography on a digoxin-ribonuclease-Sephacryl immunoadsorbent to remove antibodies which cross-reacted with digoxin, dihydrodigoxin was 300 times more effective than digoxin in inhibiting the binding of tracer by antibody. Digoxin-absorbed antidihydrodigoxin antibodies were coupled to Sephacryl and were used to develop a solid-phase radioimmunoassay capable of detecting 250 to 500 pg of dihydrodigoxin in 1 ml of human serum or urine. This radioimmunoassay has been used to define the pharmacokinetics of the metabolite in four normal human volunteers who ingested 125 to 500 micrograms of dihydrodigoxin by mouth. Dihydrodigoxin was quickly absorbed, with maximal serum concentrations achieved within 45 to 105 min, followed by a rapid fall in serum immunoreactivity over 2 to 4 hr and then by a slower, more gradual decline. The terminal half-life (beta) in serum varied from 4.24 to 11.9 hr (mean +/- S.E. = 8.1 +/- 1.3 hr). Most of the administered dose was excreted in the urine, with cumulative urinary recovery varying inversely with the dose. Urinary half-lives averaged 13.8 +/- 2.1 hr, and renal clearance rates were similar to those of creatinine. Dihydrodigoxin is rapidly absorbed and excreted in man and appears to be eliminated from the body at a faster rate than digoxin.

A cardioactive factor in human plasma with positive inotropic and positive chronotropic activities.

A cardioactive factor with a molecular weight of about 100,000 and that exhibits positive inotropic and positive chronotropic activity on isolated guinea pig atria has been found in human plasma. The positive inotropic activity is less stable than the positive chronotropic activity. The two activities move together in cation- and anion-exchange chromatography, gelfiltration chromatography, and polyethylene glycol precipitation. They may be associated with a single large polypeptide or with different subunits of a complex protein.

Mechanism of cis-platinum nephrotoxicity: I. Effects of sulfhydryl groups in rat kidneys.

cis-Diamminedichloroplatinum (CP), an important chemotherapeutic agent, produces acute renal failure by an unknown mechanism. Other heavy metals, such as mercury, are thought to be nephrotoxic by reacting with sulfhydryl (SH) groups. To investigate the mechanism of CP nephrotoxicity, F344 rats were injected once with 6 mg of CP per kg. After 96 hr, the blood urea nitrogen rose to 140 mg/100 ml. The SH concentration in control kidneys was 20.4 +/- 0.1 muml/g wet weight. Total renal SH groups decreased to a maximum of 14% at 120 hr (P less than .01). The fall in SH groups was entirely due to a decrease of protein-bound SH groups. Cell fractionation studies showed that the greatest decline of SH groups occurred in the "mitochondrial" and "cytosol" fractions. These fractions also had the highest Pt concentrations. There was no stoichiometric relationship between Pt accumulation and the change in SH groups. Furthermore, in vitro studies demonstrated that CP does not directly interact with SH groups. To determine if the change in renal SH groups was nonspecific effect of acute injury, renal failure was induced with glycerol (5 g/kg i.m.). Total SH groups per kidney increased after glycerol. These results indicate that the decrease in renal SH groups produced by CP is not due to nonspecific tubular necrosis. The present findings suggest the possibility that the nephrotoxic effects of CP may be related to depletion of SH groups. However, a direct cause-effect relationship has not been established.

A two-compartment model for digoxin disposition in dogs.

The disappearance of digoxin from heart and skeletal muscle was studied in dogs using a sequential biopsy technique. The animals were injected with digoxin for five days and subsequently with 3H-digoxin for an additional three days. 12, 24, and 48 h after discontinuation of digoxin, tissue samples of left ventricle, left atrial appendage, and skeletal muscle were taken. In addition, digoxin serum levels were measured. With the help of a computer program, a mathematical model was developed for the description of the disposition and elimination of digoxin from tissue. Disappearance from plasma and tissue was consistent with a two-compartment open model.

Renal handling of cis-diamminedichloroplatinum(II).

The renal handling of cis-diamminedichloroplatinum(II) (cisplatin) was investigated by measuring the renal clearance of creatinine and free platinum (Pt). Free Pt clearance exceeded the glomerular filtration rate, indicating secretion of cisplatin or a metabolite. These results suggest that accumulation of Pt within renal tubular cells may be related to its nephrotoxicity.

Digoxin metabolism in patients.

In 100 patients receiving digoxin to control heart disease, metabolic reduction of the lactone ring of digoxin was investigated. An average of 12.4% +/- 11% (range 2.2% to 52%) of the lipid-extractable cardenolides in a 24-hour urine sample contained the reduced lactone ring. Fifty-three excreted more than 10% while seven excreted more than 35% of these metabolic products. Reduction was not influenced by age, sex, dose, or blood level of digoxin. One patient who excreted 52% reduced products in the urine had 40% reduced digoxin-metabolites in the blood; the main metabolite was dihydrodigoxin. We found no influence of other drug therapy or concurrent disease on reduction of digoxin in this group.

[Dihydrogenated metabolites of digoxin: clinical importance and identification (author's transl)]. / Dihydrierte Metaboliten des Digoxins: klinische Bedeutung und Nachweisverfahren.

Several methods for the determination of dihydrometabolites of digoxin are described. Dihydrometabolites of digoxin are essentially inactive. They are the most important group of metabolites of digoxin. Seven (7) percent of a group of in-patients excreted more than 35% of these metabolites. The average was 13%, with respect to total extractable digoxin and metabolites in urine. In blood up to 40%, and in urine up to 52% dihydrogenated metabolites were found. The main metabolite was dihydrodigoxin, but the hydrolytic metabolites of digoxin exist also in reduced form. Neither the dose of digoxin, impaired renal function, nor an increased body content of digoxin seems to affect the rate of formation of these dihydrometabolites.

Enzymatic assay for methotrexate in serum and cerebrospinal fluid.

We describe an assay for methotrexate in biological fluids. The assay is based on inhibition by methotrexate of dihydrofolate reductase from Lactobacillus casei. The lower limit of sensitivity in serum is 2 X 10(-8) mol (about 10 mug) of methotrexate per liter. Within-run precision is +/- 5% (coefficient of variation) and day-to-day variation is 18%. Advantages of the assay are ease of manipulation, high sensitivity, and specificity.

Physiological distribution of digoxin in human heart.

Using the recipient's human heart removed at cardiac transplantation, the distribution of digoxin at both the cellular and subcellular level has been studied. In the presence of diffuse histological myocardial abnormalities tissue digoxin is decreased, but the subcellular distribution, presumably reflecting binding to a possible receptor site, is uniform. When the histological abnormality is focal then digoxin distribution is uniform.These results suggest that in the presence of myocardial ischaemia plasma digoxin concentrations may not reflect total myocardial levels accurately.

A andomized contraceptive trial comparing a daily progestogen with a combined oral contraceptive steroid.

PIP: This study was designed as a double-blind trial of .25 mg ethynodiol diacetate versus the combined, established preparation, Ovulen 21 (1 mg ethynodiol diacetate and .1 mg mestranol). Blanks were added to the sets of Ovulen 21 capsules so that there was no obvious difference in appearance of the medications. 43 young women enrolled in each group. There were more dropouts in the experimental group so that the average number of months of study was 9.2 for the control group and only 6.7 for the experimental group. The experimental group reported more intercyclic bleeding and more irregularity of cycles than the Ovulen 21 control group (p.001 in each case). Cramping was reported 3 times more frequently by the experimental group, (p.05). There was 1 unusually prolonged case of amenorrhea (7 months) in a patient taking ethynodiol diacetate. This patient responded to discontinuation of the tablet and had a menstrual cycle within 36 days. There were no unintended pregnancies.^ieng