Rapid GC method for quantitation of nifedipine in serum using electron capture detection

Voltammetric Sensing of Nifedipine Using a Glassy Carbon Electrode Modified with Carbon Nanofibers and Gold Nanoparticles

Nifedipine, a widely utilized medication, plays a crucial role in managing blood pressure in humans. Due to its global prevalence and extensive usage, close monitoring is necessary to address this widespread concern effectively. Therefore, the development of an electrochemical sensor based on a glassy carbon electrode modified with carbon nanofibers and gold nanoparticles in a Nafion® film was performed, resulting in an active electrode surface for oxidation of the nifedipine molecule. This was applied, together with a voltammetric methodology, for the analysis of nifedipine in biological and environmental samples, presenting a linear concentration range from 0.020 to 2.5 × 10-6 µmol L-1 with a limit of detection 2.8 nmol L-1. In addition, it presented a good recovery analysis in the complexity of the samples, a low deviation in the presence of interfering potentials, and good repeatability between measurements.

Pharmacokinetics of calcium channel blocking agents

Verapamil and nifedipine are the most frequently used calcium channel blocking agents in Sweden at present time. The pharmacokinetics of verapamil has been described both in healthy volunteers as well as in patients with supraventricular arrhythmias, angina pectoris, liver cirrhosis, hypertrophic cardiomyopathy or hypertension. Intravenous pharmacokinetics of nifedipine has been investigated in healthy volunteers and oral pharmacokinetics in healthy volunteers as well as in patients with hypertension. The pharmacokinetics of verapamil and of one of its metabolites, norverapamil, is changed after multiple oral dosing as has been described in patients with supraventricular tachyarrhythmias, angina pectoris or in patients with essential hypertension. Plasma concentration-effect relationships have been established for verapamil in different clinical situations and in a few cases also for nifedipine. An update of the pharmacokinetics of these two important calcium channel blocking agents is presented.

Determination of felodipine in plasma by capillary gas chromatography with electron capture detection

Felodipine in plasma was extracted with toluene and determined by automated capillary gas chromatography with electron capture detection. Undesirable oxidation of the dihydropyridine derivative in the injector and in the column was avoided by the use of glass materials with the inner surfaces treated by high-temperature silylation. The day-to-day reproducibility of the method was represented by a relative standard deviation (RSD) of 5% for a felodipine concentration of 25 nmol/l. The minimum determinable concentration (giving better than 15% RSD) was 1-2 nmol/l (0.4-0.8 ng/ml).

Detection and determination of total amlodipine by high-performance thin-layer chromatography: a useful technique for pharmacokinetic studies

A novel analytical method for determination of the total plasma levels (free and protein bound) of the calcium channel blocking agent amlodipine has been developed using a high-performance thin-layer chromatographic (HPTLC) procedure. Detection and quantitation were performed without internal standards. In previously described methods for the estimation of amlodipine by gas chromatography and high-performance liquid chromatography, only the free levels in plasma and serum were quantified at 7% of the total amlodipine level, with the remaining 93% bound to plasma protein and tissue. The present method employs proteolysis of the plasma proteins by incubating plasma for 2 h in pepsin solution. After proteolysis amlodipine is extracted and a known amount of the extract is spotted on precoated silica-gel 60 F254 plates using a Camag Linomat IV autosampler. Amlodipine was quantified using a dual-wavelength TLC scanner. The method provides a direct estimate of the total amlodipine present in plasma.

Analysis of felodipine by packed column supercritical fluid chromatography with electron capture and ultraviolet absorbance detection

A reproducible and selective supercritical fluid chromatography (SFC) method was developed for the analysis of felodipine, a drug indicated for the treatment of hypertension. Methanol-modified carbon dioxide was employed as the SFC mobile phase with both electron capture detection (ECD) and multi-wavelength detection (MWD) being used simultaneously for analyte determination. Chromatography limit of detection (LOD) and limit of quantitation (LOQ), linear dynamic range (LDR) and injection precision were obtained in order to assess chromatographic and detector performance for both the SFC/MWD and SFC/ECD/MWD systems. The method was shown to be stability indicating since felodipine could be separated from its potential oxidative degradation product, H152/37, in under 6 min (felodipine k' = 2.44). Sample throughput was increased by 60% with the SFC assay vs LC. The optimized SFC method was shown to be equivalent to an existing LC/UV procedure for the analysis of a sustained-release tablet while realizing a 92% saving in disposable solvent waste. In order to achieve further solvent savings overall, supercritical fluid extraction (SFE) with 8% methanol-modified carbon dioxide as the extraction fluid was used to extract felodipine from a sustained-release tablet (as opposed to traditional solvent extraction). Comparable drug recoveries were obtained with SFE sample preparation technique when either SFC or LC extract analysis was utilized.

Evaluation of chromatographic methods for the determination of nifedipine in human serum

Gas-liquid chromatography and high-performance liquid chromatography were compared for the identification and determination of nifedipine in biological samples and the elaboration of the optimum liquid-liquid extraction procedure. The determination limits were 2 and 10 ng/ml, respectively, and the detection limits were 1 and 5 ng/ml, respectively. The calibration graphs were linear in the ranges 2-300 and 10-500 ng/ml, respectively. Recoveries based on three different concentrations were 88.7-95.8% and 93.7-104.2%, respectively. Both methods are sensitive, specific and reproducible enough for pharmacokinetic studies and therapeutic drug monitoring.

Determination of a new calcium antagonist and its main metabolite in plasma by thermospray liquid chromatography-mass spectrometry

A highly sensitive thermospray liquid chromatographic-mass spectrometric method has been developed for the simultaneous determination of FRC-8653 (I), a new calcium antagonist, and its main metabolite (M-4) in plasma. A deuterated analogue of I was added to the plasma as the internal standard. After the purification and concentration of the plasma sample on bonded-phase disposable columns, the extract was injected into the thermospray liquid chromatograph and analysed by selected-ion monitoring mass spectrometry. The calibration curves obtained were linear over the concentration range 0.5-100 ng/ml. The limits of quantification are 0.5 ng/ml for I and 1 ng/ml for M-4 in plasma, which are sufficient to evaluate plasma concentrations after oral administration to rats.

Use of a carrier for quantitation of a new dihydropyridine calcium antagonist (OPC-13340) in human plasma by highly sensitive gas chromatography with negative-ion chemical ionization mass spectrometry

A sensitive gas chromatographic-mass spectrometric method for the quantitation of (+/-)-methyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (OPC-13340, I), a new dihydropyridine calcium antagonist with a potent and long-acting antihypertensive and antianginal effect, was developed in order to elucidate its pharmacokinetics. Dihydropyridine calcium antagonist have been usually quantifed by this technique in the negative-ion chemical ionization mode. However, direct application of this method to quantify trace amounts of I in biological fluids completely failed, owing to its adsorption on the column and oxidation of its dihydropyridine ring. Human plasma containing I and (+/-)-[2H3]methyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (II), the internal standard, was extracted with n-hexane-diethyl ether under weakly basic conditions (pH 8). In order to prevent adsorption of the compounds on the column, (+/-)-[2H5]ethyl 3-phenyl-2(E)-propenyl 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate (III), an analogue of I, was added to the extracts as a carrier. In addition, this carrier was also effective in preventing the oxidation of I. The quantitation limit of I in human plasma by this method was found to be less than 30 pg/ml. Thus, the method is sufficiently sensitive to study the pharmacokinetics of I in humans.

Clinical pharmacokinetics of calcium antagonists. An update

The calcium antagonists are valuable and widely used agents in the management of essential hypertension and angina. There is an increasing number of new agents to add to the 3 prototype substances nifedipine, diltiazem and verapamil. These new agents are dihydropyridines structurally related to nifedipine. However, they tend to have longer elimination half-lives (t 1/2 beta) and may be suitable for twice-daily administration. Amlodipine is an exception with a t 1/2 beta in excess of 30h. Apart from elimination rates, however, the pharmacokinetic characteristics of the newer agents have a notable tendency to resemble those of the established agents. They are highly cleared drugs, are relatively highly protein bound. As they are subject to significant first-pass metabolism, old age and hepatic impairment will increase their plasma concentrations due to a reduced first-pass effect. Renal impairment does little to their pharmacokinetics since the fraction eliminated unchanged by the kidney is small. For most agents, plasma concentration-response relationships have been described. Interesting areas for further research include chronopharmacokinetics, stereoselective pharmacokinetics and lipid solubility. Drugs affecting hepatic blood flow and drug metabolising capacity have predictable interaction potential. Some of the newer calcium antagonists will, like verapamil, increase plasma digoxin concentrations. Verapamil and diltiazem decrease phenazone (antipyrine) metabolism and therefore tend to decrease the metabolism of other drugs.

Determination of felodipine and its metabolites in plasma using capillary gas chromatography with electron-capture detection and their identification by gas chromatography-mass spectrometry

A novel method for the determination of felodipine and its metabolites in plasma by capillary gas chromatography (GC) with electron capture detection was developed. Felodipine and its oxidized metabolite were assayed by capillary GC after solid-phase extraction with the aid of a cool on-column injection technique. Acid metabolites, methyl monoacid and ethyl monoacid and diacid, were extracted with diethyl ether and propylated with 1-n-propyl-3-p-tolyltriazene before being submitted to capillary GC. These methods were very sensitive and useful for the pharmacokinetic study of felodipine. Felodipine and its metabolites were identified by GC-mass spectrometry. The mass spectral patterns of the peaks of extracts from human plasma samples after oral administration of felodipine were in good agreement with those of reference compounds.

Lack of effect by nifedipine on hepatic mixed function oxidase in man

Nifedipine (NF), a calcium channel blocker, is often prescribed in association with other drugs. Therefore, it was interesting to know whether or not, nifedipine, which is metabolized by the cytochrome P-450NF, was able to induce or to inhibit in vivo the activity of the hepatic mixed function oxidase system. The study was conducted in ten young healthy male volunteers receiving 20 mg NF slow release bid for 15 days. Due to the small number of subjects, comparison of the NF pharmacokinetics at dose 1 and 26 failed to show a bimodality in the frequency distribution of its area under the plasma concentration-time curve (AUC 274.5 to 317.1 ng ml-1 h, NS). Hepatic microsomal autoinduction (t1/2 2.87 to 3.06 h, NS) was not found. No statistically significant effect was seen on the aminopyrine breath test and on the debrisoquine metabolic molar ratio performed before and at the end of the treatment. Unlike what has been suggested by in vitro studies, NF treatment did not modify significantly the urinary excretion of 6 beta-hydroxycortisol (318 to 265 micrograms/d, NS). After the last dose, the total oral clearance of NF was highly correlated with the metabolic clearance to 4-hydroxyantipyrine (r = 0.88; P = 0.005) but the other parameters of antipyrine biotransformation remained unchanged. We conclude that repeated nifedipine oral intake does not modify enzymatic activities of hepatic P-450 cytochromes involved in the biotransformation of antipyrine, aminopyrine, debrisoquine and cortisol.

Analysis of nifedipine and its pyridine metabolite dehydronifedipine in blood and plasma: review and improved high-performance liquid chromatographic methodology

A reversed-phase HPLC method is described for the simultaneous determination of nifedipine and its primary pyridine metabolite dehydronifedipine in blood and plasma, that involves UV detection and neutral (blood) or alkaline (plasma) extraction. The limit of reliable determination is found to be 3 ng ml-1 with an inter-assay RSD of below 11%. In the presence of haemoglobin, nifedipine is unstable at pH greater than 10, necessitating neutral extraction for the measurement of nifedipine in haemolysed blood. Published methods for analysis of nifedipine are reviewed, emphasizing the lack of specificity and sensitivity which render many of them unsuitable for the investigation of nifedipine disposition in man.

Chromatography of calcium channel blockers

Numerous publications during the past ten years have described the determination of various calcium channel blockers in biological fluids, using gas and liquid chromatographic techniques. Diltiazem, verapamil, flunarizine and a growing number of dihydropyridines belong to this group of drugs, which in most instances are active at low plasma concentrations. From a bioanalytical point of view these compounds have many features in common, such as high lipophilicity and favourable detection properties.

Analysis of amlodipine in serum by a sensitive high-performance liquid chromatographic method with amperometric detection

An analytical method for a new calcium channel blocking agent, amlodipine, has been developed using high-performance liquid chromatography with electrochemical detection. No compound modification is required for detection and the calibration curve in spiked sera is linear and reproducible over the range 0.2-2.0 ng ml-1. The method has been applied successfully to pharmacokinetics studies in rats and also can be used for other dihydropyridine compounds such as nifedipine and nicardipine.

Radio high-performance liquid chromatographic determination of 14C-labelled LF 2-0254, A 1,4-dihydropyridine calcium antagonist, in rat and dog plasma using off-line liquid scintillation counting

LF 2-0254 is a 1,4-dihydropyridine calcium antagonist with a slow onset of action. The pharmacokinetics of [14C]LF 2-0254 were studied in rats and dogs. A sensitive high-performance liquid chromatographic method using liquid scintillation counting was developed for the quantitation of labelled LF 2-0254 in plasma. The peak height of the internal standard in the chromatogram was measured by UV detection and the mobile phase containing the chromatographic peak of [14C]LF 2-0254 was collected and counted for radioactivity. The concentration of labelled drug in the plasma was then determined using a calibration graph constructed from the determination of [14C]LF 2-0254 of known specific activities. The limit of determination was dependent on the specific activity of the drug administered. This method permits the measurement of the radioactive drug in biological fluids.

Selected ion monitoring analysis of NB-818, a new calcium entry blocker in a series of dihydropyridines, in human plasma

NB-818 is expected in clinical use to produce an antihypertensive effect and simultaneously to promote an increase in cerebral blood flow, owing to its vasodilator activity. To determine NB-818 levels in human plasma for pharmacokinetic studies, a capillary column gas chromatography/mass spectrometry/selected ion monitoring (GC/MS/SIM) method was employed. Because NB-818 was degraded under GC conditions, stable derivatives had to be prepared for GC/MS measurements. Reaction of NB-818 with silylation agents produced derivatives quantitatively. In the silylation, however, the carbomoyl group of NB-818 was replaced by silyl moieties. NB-818 is possibly metabolized at the carbamate moiety alone, giving a compound with a hydroxymethyl group in place of the carbamoyloxymethyl group. Since this compound and NB-818 gave the same derivative, efforts were devoted to separating them. A detection limit below 0.1 ng ml-1 was attained. The calibration curve was linear in the concentration range 0.1-10 ng ml-1 (r = 0.9998), and the coefficient of variation was 5.5% and 3.1% at concentrations of 1 and 10 ng ml-1, respectively.

Relation between serum nifedipine concentration and hemodynamic effects in nonobstructive hypertrophic cardiomyopathy

The relation between nifedipine concentration and hemodynamic effects after sublingual administration of 10 or 20 mg was examined in 13 patients with nonobstructive hypertrophic cardiomyopathy (HC). Serum nifedipine concentrations were determined by gas chromatography and were not related to dose. Peripheral vascular resistance decreased as a function of nifedipine concentration (r = -0.63, p less than 0.001); this was associated with a concentration-related increase in heart rate (r = 0.56, p less than 0.001) and in cardiac index (r = 0.50, p less than 0.001). However, evidence for a pure vasodilator effect of nifedipine was inconsistent, in that the change in stroke volume index with nifedipine was not significant. Although stroke volume index increased at nifedipine concentrations between 60 and 120 ng/ml (38 +/- 6 to 42 +/- 4 ml/m2, p less than 0.01), it decreased at concentrations greater than 120 ng/ml (40 +/- 3 to 38 +/- 4 ml/m2, p less than 0.01). Moreover, pulmonary artery wedge pressure increased at nifedipine concentrations greater than 120 ng/ml (11 +/- 2 to 16 +/- 4 mm Hg, p less than 0.001), suggesting either depressed left ventricular (LV) systolic function or reduced LV filling. To investigate these possible mechanisms, LV systolic and diastolic function was studied during catheterization with a nonimaging scintillation probe in 6 of the 13 patients. In these subjects, heart rate was held constant by atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of nifedipine and its three principal metabolites in plasma and urine by automated electron-capture capillary gas chromatography

A sensitive, efficient, linear and reproducible capillary gas chromatographic method with electron-capture detection was developed for the quantitation of nifedipine and its primary metabolite M-I in plasma together with the urinary and principal metabolites M-II and M-III. On-column, rather than split-splitless, injection was employed to obviate oxidative degradation of nifedipine to M-I. The photosensitivity of nifedipine was re-examined under laboratory conditions and nifedipine was found to have a half-life in excess of two days when amber glassware and darkroom manipulations under red light were used. The method can determine nifedipine and its metabolites in plasma and urine after a single oral dose of 5 mg and can be applied to measure M-I production by human liver microsomes.

Pharmacokinetics and pharmacodynamics of nifedipine in patients at steady state

The pharmacokinetics and associated pharmacodynamics of nifedipine were studied at steady state in 12 patients with angina pectoris who were receiving nifedipine 10-40 mg tid. After dosing, serum nifedipine concentrations rose rapidly and decayed in a log-linear fashion. The mean (+/- SEM) maximum serum concentration (Cmax) after dose normalization, and the time to Cmax (tmax) were 115 +/- 7 ng/mL and 0.72 +/- 0.13 hr, respectively. The mean area under the plasma concentration-time curve per 10-mg dose was 304 +/- 34 hr-ng/mL. The average elimination rate constant was 0.205 +/- 0.016 hr, and the harmonic mean elimination half-life was 3.4 hr (range, 2.5-4.9 hr). Heart rate increased (5-6 beats/min, P less than .05) from baseline for up to one hour after dose, while mean diastolic blood pressure decreased (6-15 mm Hg, P less than .05) for up to four hours. Cardiac output was increased (1.1-2.8 L/min, P less than .05), and calculated total systemic resistance (3.8-6.3 mm Hg/L/min, P less than .05) was decreased for the entire dosing interval after nifedipine dosing. Hysteresis plots for heart rate and mean diastolic blood pressure showed a time lag between changes in serum nifedipine concentrations and heart rate, but not between serum nifedipine concentrations and blood pressure. Changes in cardiac output did not correlate with serum nifedipine concentrations. The steady-state kinetic and dynamic parameter values in patients with angina pectoris in this study were similar to those found in healthy volunteers or hypertensive patients after acute nifedipine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of nifedipine after multiple doses

The single and multiple dose pharmacokinetics of oral nifedipine capsules, 10 mg, have been examined in five patients with peripheral vasospasm. After a single dose, nifedipine was rapidly absorbed in three and slowly absorbed in two patients. Mean bioavailability parameters included a tmax of 2.9 h, a Cmax of 33.3 ng ml-1 and a AUC0-8 h of 113.3 ng h ml-1. After multiple dosing with either 10 or 20 mg every 8 h for 10 days the mean tmax at steady state was 2.1 h while the mean dose-corrected (to 10 mg) Cmax and AUC0-8 h were 51.9 ng ml-1 and 146.9 ng h ml-1, respectively. The mean elimination rate constant was 0.173 h-1 after both single and multiple doses. The mean extent of accumulation of nifedipine, defined as the ratio of AUC0-8 h (steady state)/AUC0-8 h (single dose), was 1.3; we concluded that nifedipine accumulates in the body when it is administered every 8 h. This should be taken into account when predicting steady state serum concentrations and haemodynamic effects of nifedipine from single dose kinetic data.

Combined capillary column gas chromatography/electron capture negative ion chemical ionization mass spectrometry of dihydropyridine calcium antagonists

Several dihydropyridine calcium antagonists showed intense [M]-. ion peaks as the base peaks and a few fragment peaks in the electron capture negative ion chemical ionization mass spectra. The peak intensities of the [M]-. ion of these antagonists were about 100 times as high as those of the most abundant positive ion. The use of a capillary column connected directly to the ion source prevents the oxidation of these agents in the column and the transfer line. Furthermore, the presence of plasma extract decreases the oxidation of these agents in the injection port. The limits of sensitivity with this technique are 500 fg-5 pg on the column. Combined capillary column gas chromatography/electron capture negative ion chemical ionization mass spectrometry should be suitable for sensitive and specific assays of dihydropyridine calcium antagonists in biological fluids.

Protein binding of nifedipine

The protein binding of nifedipine in concentrations up to 1200 ng ml-1 has been measured in serum, pure human albumin solution and pure human alpha 1-acid glycoprotein (AAG) solutions by ultrafiltration. The drug was extensively bound in serum from four healthy volunteers with a mean (+/- s.d.) fraction bound of 0.992 +/- 0.008. In albumin solution (40 g litre-1) the mean (+/- s.d.) fraction bound 0.970 +/- 0.012, was not significantly different (P greater than 0.05) from that in serum, suggesting that albumin is the major, but not necessarily the only, binding protein for nifedipine in serum. The binding of nifedipine in solutions of AAG was proportional to the AAG concentration and ranged from 0.514 +/- 0.059 to 0.755 +/- 0.035 in solutions containing 50 and 150 mg % AAG, respectively. Binding of nifedipine in all protein solutions was linear.

Quantitative analysis of the dihydropyridines, 3-(2-furoyl)-5-methoxycarbonyl-2,6-dimethyl-4-(2-nitrophenyl)- 1,4-dihydropyridine and nifedipine, by high-performance liquid chromatography with electrochemical detection

An analytical method based on solvent extraction and reversed-phase high-performance liquid chromatographic separation with electrochemical detection has been developed for the dihydropyridines, 3-(2-furoyl)-5-methoxycarbonyl-2,6-dimethyl-4-(2-nitrophenyl) -1,4-dihydropyridine (MDL 72.567) and nifedipine. The analysis includes an internal standard of similar light sensitivity to correct for possible photodegradation during the procedure. The specificity of electrochemical detection precludes interference from oxidized metabolites. Total analysis time was 35 min per sample, and the detection limit for quantification was 1-2 ng/ml. Linear regression analysis gave calibration curves with coefficients or correlation of 0.9992 for MDL 72.567 (1-100 ng) and 0.997 for nifedipine (1-50 ng). Assays for within-run and day-to-day reproducibility gave coefficients of variation of 3.9% and 6.0%, respectively, at concentrations of 50 ng/ml. The method has been applied to the analysis of plasma levels of nifedipine and MDL 72.567 in dogs.

Determination of nilvadipine in human plasma by capillary column gas chromatography-negative-ion chemical-ionization mass spectrometry

A highly sensitive and specific method for the determination of nilvadipine, a new dihydropyridine calcium antagonist, in human plasma is described. A deuterated analogue of nilvadipine is added to the plasma as an internal standard. The agent and its internal standard are extracted at pH 9 from the plasma into a benzene--n-hexane (1:1) mixture. The extract is analysed by fused-silica capillary column gas chromatography--negative-ion chemical-ionization mass spectrometry with methane as the reagent gas. The mass spectrometer is set to monitor the negative molecular ions of the agent and internal standard. Quantitation is possible down to 0.01 ng/ml using 1 ml of plasma. The coefficients of variation of the method are 6.4 and 2.1% at the 0.01 and 0.1 ng/ml levels, respectively. Plasma levels obtained with this method are given for four healthy volunteers who had received a 6-mg oral dose of nilvadipine.

Determination of nifedipine in human plasma by high-performance liquid chromatography with electrochemical detection

A rapid, accurate and sensitive high-performance liquid chromatographic assay was developed for the determination of nifedipine in human plasma. A toluene extract of an alkalinized plasma sample was chromatographed on a reversed-phase column with electrochemical detection at +0.95 V. The recovery of nifedipine from plasma was about 100%. The detection limit for nifedipine in plasma was 2 ng/ml using 0.5 ml of sample. The assay gave a linear response over the concentration range 5-400 ng/ml in plasma. The coefficients of variation from 9.6 to 191.0 ng/ml varied between 5.2 to 1.0% and the accuracy did not exceed 3.0%. Photodegradation products and metabolites of nifedipine did not interfere in the analysis. This method allowed the behaviour of nifedipine in humans to be studied.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.