Interaction between digoxin and calcium antagonists and antiarrhythmic drugs.

The influence of several calcium antagonists and antiarrhythmic drugs on digoxin kinetics and actions were investigated in 36 healthy men during digoxin steady state (0.375 mg/day). The subjects were randomly assigned to three subgroups and each group received placebo (control) and two of the following regimens (doses three times a day) in a randomized sequence for 2 wk each: verapamil (80 mg) and nifedipine (10 mg), verapamil (120 mg) and gallopamil (50 mg), or propafenone (150 mg) and quinidine (250 mg). Plasma digoxin concentration (PDC) rose during the cotreatments in the sequence: gallopamil (+16%) less than propafenone (+37%) less than nifedipine (+45%) less than verapamil (almost independent of dose, +69%) less than quinidine (+118%). These increases in PDC correlated closely to decreases in renal digoxin clearances. Renal creatinine clearance was virtually unaffected. The rise of PDC resulted in increased glycoside effects, as measured by the shortening of systolic time intervals and flattening of T wave. There was a linear correlation between PDC and changes in mean corrected electromechanical systole and T wave flattening. We conclude that, in addition to quinidine, other antiarrhythmic drugs and various calcium antagonists interact kinetically with digoxin and that the increasing PDCs are cardioactive.

Quinidine-digoxin interaction: cardiac efficacy of elevated serum digoxin concentration.

Cardioactivity due to elevated serum digoxin concentration (SDC) after quinidine (Q) and digoxin (D) was evaluated in six healthy subjects by means of measurement of systolic time intervals (STIs). Each subject randomly received basic treatments with 0.2 mg D and placebo (PL1). Randomized coadministrations with Q (1 gm/day), sparteine (SP) (0.8 gm/day), and placebo (PL2) were given for 7-day periods. A steady-state dose of 0.4 mg D was added. Mean SDC increased from 0.48 ng/ml during 0.2 mg D + PL2 to 1.13 ng/ml on 0.2 mg D + Q (P less than 0.05); it was unchanged by SP. On 0.4 mg D there were further shortenings of STIs compared to those on 0.2 mg D + PL2. Q markedly prolonged STIs; the SP effects were similar but less pronounced. When given with Q or SP, the effect of D was obscured by opposing inotropic properties; consequently, despite increasing SDC, measureable STIs were unchanged. The true glycoside effect was determined by comparing the effects of the pure antiarrhythmic to those of the antiarrhythmic with D. These calculations showed that the glycoside effect of the elevated SDC during Q + D dosing was much the same as the effect of 0.4 mg D.

Pharmacokinetic interaction study with ramipril and digoxin in healthy volunteers.

Coadministration of captopril has been shown to increase serum digoxin concentration. The effects of ramipril, a new angiotensin converting enzyme inhibitor, on serum digoxin concentration after multiple dosing were studied in 12 healthy volunteers. All subjects were receiving steady-state digoxin medication (0.5 mg daily), and ramipril (5 mg daily) was coadministered for 14 days. Serum digoxin concentration was measured repeatedly before, during and up to 1 week after ramipril coadministration at 8 a.m. (trough values) and on selected trial days at 11 a.m., 3 hours after the morning medication. Simultaneously, blood levels of ramipril and its active metabolite diacid were determined. Volunteers were followed closely for side effects and for changes in blood pressure, heart rate and electrocardiogram. Safety pharmacology included serial determination of sodium, potassium, serum glutamic oxaloacetic transaminase, creatinine and a full blood count. Mean serum digoxin concentration was not significantly influenced by ramipril coadministration with trough levels of 0.90 +/- 0.24 before, 0.93 +/- 0.38 during and 0.82 +/- 0.33 ng/ml after ramipril medication. The increase in serum digoxin concentration 3 hours after the morning dose was also not significantly affected by ramipril. Serum levels of ramipril and its diacid showed a wide range of variation. Mean serum potassium increased by 0.3 mmol/liter during ramipril coadministration with development of symptomless hyperkalemia (6.0 mmol/liter) in 1 subject. The only other side effect possibly related to ramipril was a dry cough in 1 subject. Both drugs were well tolerated. Ramipril showed no significant influence on serum digoxin levels in healthy volunteers.

Influence of severity of heart failure on the efficacy of angiotensin-converting enzyme inhibition.

Angiotensin-converting enzyme (ACE) inhibition slowed the progression of congestive heart failure (CHF) in 170 patients who were randomly assigned to either captopril or placebo in the Munich Mild Heart Failure Trial. The two major end points were progression from New York Heart Association (NYHA) functional classes I, II, or III to class IV, despite optimal, adjusted standard therapy, and death due to CHF. The relative risk for progressive CHF with captopril therapy was 0.34 (95% confidence interval = 0.17-0.68; p = 0.01). A total of 52 prerandomization variables were tested to determine their contribution to disease progression. Logistic regression analysis revealed 5 independent risk factors for progressive CHF: NYHA class, left ventricular end-systolic diameter, need for diuretic, age, and cardiothoracic ratio. The presence of greater than 2 of these risk factors increased the odds ratio for progression to 8.13 (p less than 0.001) compared with the presence of 0-2 risk factors. However, the effectiveness of captopril in preventing progression was higher within the subgroup of patients who had less severe CHF: the odds ratio was 0.12 (95% confidence interval = 0.03-0.45; p less than 0.01) for patients in NYHA class I or II on captopril and was 0.83 for those in class III. We conclude that the severity of CHF, as represented by the above-defined risk factors, is directly related to the likelihood for the development of progressive heart failure. However, the less severe the heart failure, the more effective the treatment with captopril will be in preventing disease progression. Thus, ACE inhibition has considerable potential for improving the prognosis of patients with mild heart failure.

Angiotensin-converting enzyme inhibitors in preventing remodeling and development of heart failure after acute myocardial infarction: results of the German multicenter study of the effects of captopril on cardiopulmonary exercise parameters (ECCE).

Early action of angiotensin-converting enzyme (ACE) inhibitors after myocardial infarction (MI) has been shown in large scale clinical trials to reduce mortality over the first weeks. However, the mechanisms involved are yet unclear and several trials showed a tendency toward a small, albeit unexpected, rise in cardiogenic shock or mortality. Since cardiopulmonary exercise testing (CPX) has become a "gold standard" in assessing the severity of heart failure, we studied--after finishing a pilot trial--the effect of captopril versus placebo in 208 patients who were individually titrated (titrated dose, mean 46/69 mg/day after 7 days/4 weeks, respectively) in order to preserve their blood pressure in the acute phase of myocardial infarction; we followed the development of congestive heart failure (CHF) over 4 weeks by measuring oxygen consumption. After 4 weeks, overall oxygen consumption at the anaerobic threshold (VO2-AT; 13.7 vs 13.1), maximal oxygen consumption (VO2max 19.3 vs 18.9 mL/kg per min) and exercise duration (896 vs 839 sec) showed a nonsignificant difference in favor of the captopril group. The predefined, categorized, combined endpoint of severe heart failure or death (heart failure necessitating ACE inhibition, VO2max < 10 mL/kg per min, or death) was significantly reduced in the captopril group (n = 7/104) versus placebo (n = 18/104; p = 0.03). Differences were mainly caused by fewer CHF events (delta n = 10). We conclude that ACE inhibition with individualized dose titration markedly reduces the 4-week incidence of severe heart failure or death; > 10 patients per 100 treated gained major benefits from this therapy.

Influence of quinidine on the intestinal secretion of digoxin and digitoxin in guinea pigs.

The secretion of digoxin and digitoxin into in situ perfused jejunal and colonic segments of normal or quinidine treated guinea pigs was studied. Quinidine was administered intravenously by constant rate infusion resulting in a quinidine plasma concentration of about 6 micrograms/ml. After 2 h digoxin or digitoxin was injected i.v. (10 micrograms/kg). The quinidine treatment enhanced the plasma concentration of [3H]digoxin to about 140% as compared to controls, whereas the [3H]digitoxin concentration was not influenced by the quinidine infusion. Both, digoxin and digitoxin were secreted against a concentration gradient into the intestinal lumen. During the experimental period of 180 min controls secreted 0.24% of the administered digoxin dose per cm of jejunal and 0.13% per cm of colonic segment. Quinidine treatment resulted in a decrease of the jejunal digoxin secretion to about 80% of the control values. In both, jejunum and colon the concentration ratio between lumen and plasma (L/P) was diminished by quinidine to 50% as compared with the controls. The amount of [3H]digitoxin secreted into the intestinal segments was decreased by quinidine from 0.19% of the dose/cm to 0.13% in the jejunal and from 0.17% to 0.12% in the colonic segments, respectively. The decrease of the L/P ratio for [3H]digitoxin was more pronounced in the colon (58%) than in the jejunum (77% of the control values). As compared with controls the content of [3H]digoxin in the jejunal as well as colonic tissue was decreased by quinidine to 60% or 73%, respectively. On the other hand quinidine increased the tissue content of [3H]digitoxin in jejunum (+56%) and colon (+88%). In conclusion quinidine inhibits the intestinal secretion of both, digoxin and digitoxin, possibly by different mechanisms.

Detection of human viral RNA via a combined fluorescence and SERS molecular beacon assay.

A dual-mode molecular beacon on a multiplexed substrate has been developed and applied to the measurement of unlabeled human viral RNA. The detection system is based on a combined surface-enhanced Raman scattering (SERS) and fluorescent molecular beacon assay that is assembled on Nanobarcodes™ particles. In this assay, a molecular beacon probe terminated with a fluorescent Raman label dye is conjugated to the metallic Nanobarcodes™ particles. The molecular beacon probe is a single-stranded oligonucleotide that has been designed with a hairpin structure that holds the dye at 3'-end close to the particle surface when the probe is attached through a 5'-thiol group. In this configuration, the SERS spectrum of the label was obtained and its fluorescence quenched because the dye is in very close proximity to a noble metal surface with nanoscale features (Nanobarcodes™ particles). The SERS signal decreased and the fluorescence signal increased when target viral RNA was captured by this molecular beacon probe. In addition, a hepatitis C virus reverse transcriptase-polymerase chain reaction (HCV RT-PCR) product was detected using this dual-mode beacon. The development of a multiplexed, label-free assay system with the reassurance offered by detection of two distinctly separate signals offers significant benefits for rapid molecular diagnostics.

Quinidine-digoxin interaction: Pharmacokinetics, underlying mechanism and clinical implications.

Administration of quinidine with digoxin increased serum digoxin concentrations in 79 patients and five volunteers. In 38 patients on a constant glycoside maintenance dose, the addition of quinidine to digoxin therapy resulted in a mean 2.5-fold increase (from 0.98 +/- 0.37 to 2.47 +/- 0.71 ng per milliliter, mean +/- 1 S.D.) (P less than 0.001). The addition of quinidine decreased renal glycoside clearance (from 91.6 +/- 27.8 to 40.6 +/- 15.8 ml per minute) (P less than 0.001). Unlike other investigations, our studies provided no evidence that quinidine displaced digoxin at specific cardiac binding sites. The elevated digoxin levels found during quinidine administration suggest a 30 to 50 per cent reduction of the digoxin dose. Adverse reactions to combined quinidine-digoxin therapy may be partly due to digitalis intoxication.

Effect of coadministration of verapamil and quinidine on serum digoxin concentration.

Both quinidine and verapamil are known to increase the serum digoxin concentration (SDC), and other calcium channel blockers may have a similar effect. Since an increasing number of patients is likely to be treated concurrently with digoxin, quinidine and a calcium channel blocker, a study was done to show whether coadministered quinidine and verapamil would cooperate to elevate the SDC. Nine healthy volunteers on basic digoxin treatment (Leanoxin 0.125 mg t.i.d.) were treated with placebo, verapamil 80 mg t.i.d. and the combination (verapamil 80 mg plus quinidine base 160 mg t.i.d.), for 2 weeks in a randomized sequence. Drug concentration and various cardiovascular parameters were measured each week and/or at the end of each treatment period. Steady state concentrations were always obtained within 1 week and drug levels at the end of the first and second weeks of treatment were almost identical. The plasma verapamil concentration (PVC) was 25.8 +/- 9.9 ng/ml during coadministration of verapamil and digoxin, and 15.7 +/- 6.9 ng/ml during combined verapamil-quinidine coadministration, when the serum quinidine concentration (SQC) was 1.26 +/- 0.50 micrograms/ml. Compared to placebo SDC rose by 53% from 0.62 +/- 0.16 to 0.95 +/- 0.29 ng/ml (p less than 0.001) during verapamil treatment and further to 1.58 +/- 0.38 ng/ml (155% rise; p less than 0.001) during combined verapamil-quinidine coadministration. Thus each drug maintained its own effect on SDC in the presence of the other, and their actions became combined in increasing the SDC.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of upwardly revised DeltaH(f) of primary, secondary, and tertiary radicals on mechanistic constructs in thermal reorganizations.

Impetus for upward revision in the heats of formation of the ethyl (primary), isopropyl (secondary), and t-butyl (tertiary) free radicals has gained sufficient momentum in the last 6 yr to prompt an illustrative assessment of the far-ranging implications for interpretation of thermal reorganizations. Previous obstacles to consideration of diradicals as transition states in rearrangements of cyclopropanes and cyclobutanes are removed. The energetic relation of cyclohexa-1,4-diyl as an intermediate diradical in the Cope rearrangement to the transition state of a concerted mechanism is clarified.

[Effect of tiaprofenic acid on serum digoxin concentration]. / Der Einfluss von Tiaprofensäure auf die Digoxin-Konzentration im Serum.

The effect of concomitant tiaprofenic acid (Surgam) administration (200 mg t.i.d.) on serum digoxin concentration (SDC) was evaluated in 12 healthy volunteers on digoxin maintenance treatment. During a 10-day coadministration period with tiaprofenic acid no significant increase in SDC was observed (0.97 +/- 0.24 vs. 1.12 +/- 0.21 ng/ml, p less than 0.05). Mean tiaprofenic acid concentration amounted to 2.85 +/- 1.94 micrograms/ml 14 h after last drug intake. The incidence of adverse reactions was minimal with gastrointestinal upset in one person. Tiaprofenic acid had no influence on red or white blood cell count. Thus, in contrast to various other nonsteroidal antiinflammatory drugs coadministration of tiaprofenic acid (600 mg daily) has no relevant influence on serum digoxin levels.

[The influence of quinidine on serum digoxin concentrations (author's transl)]. / Anstieg der Digoxinkonzentration im Serum unter Chinidinmedikation.

We were able to demonstrate a significant rise of serum digoxin concentrations (SDC) under simultaneous quinidine-glycoside therapy. The reason for this elevation is not yet known. In vitro studies under addition of quinidine showed no influence on the SDC-values measured by a tritium-labelled radioimmunoassay. The mean SDC of 18 patients under simultaneous quinidine therapy was 2.39 +/- 0.84 ng/ml (3.06 +/- 1.08 nmol/l) compared to a mean SDC of 1.23 +/- 0.74 ng/ml (1.57 +/- 0.95 nmol/l) of 11 patients without quinidine therapy (p less than 0.001). Both groups of patients received the same maintenance dose and showed no obvious impairment of renal function and no significant difference in mean body weight. Our results suggest that part of the great number of adverse reactions seen under a combined glycoside-quinidine therapy might be due to the elevated SDC-values. For these patients a low-normal glycoside maintenance dose and an early reduction of the quinidine dose is recommended.

[A simplified radioimmunoassay for digoxin determination using a 125-j-labelled, solid-phase kit (author's transl)]. / Vereinfachte Serum-Digoxin-Bestimmung mit einem Jod-125-Solid-Phase-Test.

Our experience with a commercially available kit (Radioimmunoassay DIGOXIN, Boehringer, Mannheim) using (125J)-labelled digoxin and antibody-coated tubes is reported. This simplified method requires only two pepetting steps per sample and results can be obtained in 70 min. The intra- and interassay coefficient of variation ranged between 7% and 8%. The specific digoxin antibody gave no clinical relevant cross-reactions with spironolactone or prednisone (less than 0.0007%). Of the digoxin metabolites the aglucone digoxigenin showed 31% cross-reaction while the more important cardioactive metabolites digoxigenin-bis- and mono-digitoxide had the same binding affinity to the antibody as digoxin, beta-methyldigoxin and beta-acetyldigoxin. Cross-reaction with digitoxin was 6.8%. More than double-fold dilution of serum protein concentration showed little influence on the digoxin values measured. The results obtained by this new kit compare closely with those obtained by our tritium-labelled kit (r = 0.94, p less than 0.001). Therefore, the upper therapeutic limit of 1.9 ng/ml can be adopted for this method.

The quinidine-digoxin interaction in patients with impaired renal function.

Quinidine has been reported to reduce clearance and the distribution volume of digoxin. Data are presented indicating that serum digoxin concentration (SDC) is increased throughout the coadministration of quinidine. This strongly suggests that the quinidine-induced reduction of digoxin clearance is the main mechanism underlying this drug interaction. It has been suggested that beside renal clearance quinidine also reduces non-renal clearance of digoxin. Direct evidence is provided by a study in patients with impaired renal function. Irrespective of the degree of renal impairment, quinidine increases SDC to about the same amount as found in patients with normal renal function. Since quinidine does not interfere with plasma protein binding of digoxin, this implies a decrease in non-renal clearance. In all patient groups the incidence of this drug interaction is rather high; however, pronounced interindividual differences occur as regards the extent of the increase in SDC. Regardless of the state of renal function careful monitoring of digitalized patients is mandatory once quinidine therapy is initiated. Since it may take a week or more until a new steady state is established in patients with impaired renal function, this period of close monitoring should be extended correspondingly.

[Prognosis of mild chronic heart failure: effects of the ACE inhibitor captopril]. / Prognose bei leichter chronischer Herzinsuffizienz: Einflüsse des ACE-Hemmers Captopril.

UNLABELLED: The Munich Mild Heart Failure Trial (MHFT) investigated the influences of ACE-inhibition on progression of congestive heart failure (CHF). Major end points were progression of CHF from New York Heart Association (NYHA) functional classes I to III to NYHA functional class IV despite optimal adjusted standard therapy and death due to congestive heart failure, i.e. death due to pump failure or sudden death. 170 patients were randomly assigned to treatment with either captopril (n = 83) 25 mg b.i.d. or placebo in addition to standard therapy for a median observation period of 2.7 years. The major result of this trial was the decrease in the relative risk for progressive heart failure by captopril therapy to 34% (95% confidence interval 17 to 68%; p = 0.01). Though total mortality was not reduced, death due to pump failure was found considerably less often on captopril than on placebo (18.2 vs 50% of total deaths in each group). In addition this report describes influences of captopril therapy on left ventricular size and function, heart size on X-ray, influences on symptomatology, electrolytes, ventricular arrhythmias, on concomitant therapy as well as effects in various subgroups. The major finding of the trial--the influence on progression of CHF--was independent of the underlying cardiac disease and was consistent in subgroups with different etiology of heart failure. Captopril blunted the increase in norepinephrine levels usually seen with increasing severity of congestive heart failure. There was a significant increase in serum sodium and potassium levels in the captopril treated group. Left ventricular size and function were well preserved in the patients still on randomized therapy after two years. No effects of therapy on ventricular ectopic activity were found in a subgroup of 93 patients that had had Holter monitoring. IN CONCLUSION: Captopril has marked effects on progression of disease and reduces the likelihood of progressive heart failure in patients with mild symptoms. Several indices of unfavourable prognosis are either improved (sodium, norepinephrine, angiotensin II) or stabilized (left ventricular function). Thus ACE-inhibitors are to be considered for all patients requiring medical therapy for congestive heart failure.

[A questionnaire for early recognition of digitalis intoxication (author's transl)]. / Früherfassung der Digitalisintoxikation mit einem Fragebogen.

The diagnostically relevant data of 1164 patients under digitalis were stored in a computer and compared statistically for toxic and nontoxic patients. Resulting from this a questionnaire was developed in which each item was weighted according to its own diagnostic value. In a prospective study 77 suspected cases of digitalis intoxication were classified according to their scoring in the questionnaire. In 92% of the patients this classification was confirmed by the final diagnosis (after withdrawal of the glycoside). Mean score and mean serum digoxin concentration (SDC) of the toxic patients were significantly higher. There was a high consensus between the final diagnosis, the classification by the questionnaire and the SDC. The questionnaire proved to be a useful aid in the bedside diagnosis of digitalis intoxication.

[Ergospirometry in the evaluation of cardiovascular drugs]. / Spiroergometrie in der Beurteilung kardiovaskulärer Pharmaka.

In the evaluation of drugs intended to alleviate symptomatology and to improve exercise capacity in congestive heart failure, various pathophysiologic mechanisms including impairment of cardiac output, oxygenation of blood, muscle blood flow, and muscle metabolism have to be considered. In various forms of acute and chronic heart failure these mechanisms contribute more or less to impaired oxygen uptake. In acute forms of heart failure pulmonary congestion and its effects on airway resistance and lung capacity might be the predominating mechanisms of symptoms, while in chronic heart failure impedement of muscle blood flow and metabolic changes, comparable with deconditioning, are additional pathomechanisms. The increase in cardiac output and in muscle blood flow provided by some positive inotropic agents and by vasodilators after acute administration is often paralleled by a decrease in arteriovenous oxygen difference and does not lead to an improvement of oxygen uptake. However, chronic therapy with some vasodilators can lead to improvement in oxygen uptake, either due to training effects or due to flow dependent or direct effects on muscle metabolism. In pulmonary congestion a decrease of elevated filling pressures can acutely lead to some improvement of exercise capacity. Furthermore, chronic decrease in filling pressures by administration of diuretics, nitrates, ACE-inhibitors or dopaminergic drugs leads to long-term improvement in oxygen uptake. By comparing hemodynamic effects of acute and chronic drug therapy in CHF with their effects on exercise capacity, the chronic decrease of filling pressures seems to be the major hemodynamic variable leading to improvement of exercise capacity.(ABSTRACT TRUNCATED AT 250 WORDS)