β-Blocking Agents: Determination of Biological Levels Using High Performance Liquid Chromatography

Enantioselective determination of oxprenolol in human plasma using dialysis coupled on-line to reversed-phase chiral liquid chromatography

A fully automated method for the determination of the enantiomers of oxprenolol in human plasma was developed, involving dialysis through a cellulose acetate membrane, clean-up and enrichment of the dialysate on a short precolumn and subsequent chiral liquid chromatographic (LC) analysis. All sample handling operations were executed automatically by a sample processor equipped with a robotic arm (ASTED system). The trace enrichment column (TEC) was packed with octadecylsilica. After conditioning of the TEC with the LC mobile phase and pH 3.0 acetate buffer. After the enrichment step, the analyte was transferred by the LC mobile phase to the analytical column by means of a switching valve. The influence of different parameters of the dialysis process on the recovery of oxprenolol was first investigated using achiral LC conditions. The volume as well as the aspirating and dispensing flow rates of the acceptor solution were the main parameters studied. Oxprenolol was separated on a C18 stationary phase used for the enantioseparation of oxprenolol was a Chiralcel OD-R column which contained cellulose tris (3,5-dimethylphenylcarbamate) coated on silica as chiral selector. The corresponding mobile phase consisted of a mixture of pH 6.0 phosphate buffer containing NaClO4 at 0.45 M concentration and acetonitrile (70:30 v/v). UV detection was performed at 273 nm. The method developed was validated. Recoveries for each enantiomer of oxprenolol were about 80%. The method was found to be linear in the 50-2500 ng ml-1 concentration range (r2 = 0.999 for both enantiomers) and good results with respect to intra- and inter-day reproducibility as well as accuracy were obtained.

Dose proportional absorption of 25-150 mg atenolol

We investigated the dose proportionality after the intake of oral atenolol 25, 50, 100 and 150 mg. Standard tablets were taken by 8 healthy volunteers in randomised order of doses. The area under the curve divided by dose did not differ between the doses, indicating that the absorption of this hydrophilic compound, with known incomplete bioavailability, was constant over the range tested.

Rapid high-performance liquid chromatographic method for the determination of propranolol levels in canine and feline plasma

A sensitive high-performance liquid chromatographic method that does not require organic extraction has been developed for the determination of propranolol levels in canine and feline plasma. Equal volumes of plasma and a mixture of methanol-acetonitrile-0.1 M sodium hydroxide (3:3:4, v/v/v) were added to a microseparation unit with a 10,000 molecular mass cut-off filter. The ultrafiltrate was analyzed by reversed-phase liquid chromatography with fluorimetric detection. The consistency of the recoveries obtained eliminated the need for an internal standard (coefficients of variation less than 4%). Linear regressions for the standard curves (2.5-100 ng/ml) gave correlation coefficients above 0.9955. The detection limit was 1 ng/ml. The assay retains high sensitivity while eliminating laborious sample preparation.

The interactions between nisoldipine and two beta-adrenoceptor antagonists--atenolol and propranolol

1. The interactions between the dihydropyridine calcium antagonist nisoldipine and two beta-adrenoceptor blocker drugs (atenolol and propranolol) were investigated in two groups of healthy normotensive subjects. 2. The steady state plasma concentrations of both beta-adrenoceptor blockers were significantly altered by the addition of nisoldipine: for propranolol there were significant increases in Cmax, by about 50%, and in AUC by about 30% and for atenolol there was a significant increase in Cmax, by about 20%. 3. The addition of nisoldipine was also associated with significant changes in apparent liver blood flow (measured by indocyanine green clearance) from 1.4 to 2.4 l min-1 in the atenolol group and from 1.3 to 2.3 l min-1 in the propranolol group. 4. Both nisoldipine-beta-adrenoceptor blocker combinations were associated with small enhanced blood pressure reductions e.g. from 104/60 with atenolol alone to 98/50 mm Hg with the combination but there was no alteration to the extent of beta-adrenoceptor blockade (as assessed by bicycle ergometry). 5. This pharmacodynamic profile in healthy normotensives is consistent with the known therapeutic efficacy of such combination treatments in patients with hypertension and angina. 6. It is suggested that there is a pharmacokinetic component to the efficacy of this type of combination, perhaps reflecting vasodilator-induced changes in drug absorption and/or hepatic extraction.

Evaluation of potential pharmacodynamic and pharmacokinetic interactions between verapamil and propranolol in normal subjects

1. Potential pharmacodynamic and pharmacokinetic interactions between verapamil and propranolol were evaluated in two double-blind, randomised, balanced, crossover studies employing the same six healthy males. 2. The first study examined the effect of repeated propranolol administration on the pharmacodynamics and pharmacokinetics of verapamil after single oral and intravenous doses. The second explored the pharmacodynamics and pharmacokinetics of verapamil and propranolol alone and in combination after single and repeated oral doses. 3. The magnitude of the prolongation of PR interval induced by oral and intravenous verapamil was not affected by pre-treatment with propranolol. When verapamil and propranolol were co-administered as single doses, effects on PR interval were additive but, following repeated doses, a trend towards greater than additive prolongation was seen. The arithmetic sum of the effects of the two drugs was 23% (95% C.I. 8-38%) but the measured increase after the combination was 40% (95% C.I. 26-54%). 4. The extent of reduction in heart rate and blood pressure at rest and after exercise following repeated doses of propranolol was not influenced by single oral or intravenous doses of verapamil. The heart rate and blood pressure responses to single and repeated oral doses of verapamil and propranolol in combination were significantly greater than those after either drug alone and approximated to the arithmetic sum of the individual responses. 5. Although repeated administration of propranolol reduced hepatic blood flow as assessed by indocyanine green clearance, there was no evidence of an interaction between the drugs at this level. 6. The pharmacokinetics of verapamil and norverapamil were not significantly affected by prior propranolol. After single doses of verapamil and propranolol in combination, the maximum plasma concentration of propranolol was increased and the oral clearance of verapamil reduced. No pharmacokinetic interaction was observed after repeated doses. 7. These findings provide little evidence of a pharmacodynamic or pharmacokinetic interaction between verapamil and propranolol in normal subjects. Most of the haemodynamic responses to these drugs in combination can be explained by additive drug effects but an interaction affecting AV conduction after repeated doses cannot be excluded. The minor pharmacokinetic interaction between the drugs is unlikely to be relevant to the pharmacodynamic changes.

A sensitive radioligand binding assay for timolol in plasma

A sensitive and reproducible radioreceptor assay (RRA) is described for the determination of low picogram levels of timolol in plasma. The plasma or serum samples (1 mL) are prepared by selectively extracting timolol with lipophilic solvents or, alternatively, only plasma (serum) proteins are precipitated prior to binding assay. The recovery of timolol is at least 90% during the sample preparation. In the radioligand binding assay, timolol and the nonselective beta-antagonist [3H](-)-CGP-12177 compete for the binding sites present in the rat reticulocyte membranes. The detection limit for timolol (30 pg/mL) exceeds 50 times the sensitivity of the GC-MS techniques for timolol. The RRA results and GC results obtained from the same clinical samples correlate excellently (r = 0.99). There was no evidence for interference caused by timolol metabolites in the RRA. Timolol concentrations in plasma following its oral and even ocular administration were possible to monitor using the RRA. The method can be modified to also measure several other beta-antagonist drugs in picogram per milliliter quantities.

Finite dose percutaneous drug absorption: theory and its application to in vitro timolol permeation

The finite dose in vitro percutaneous absorption kinetics of timolol, a beta-blocker, was studied. The flux of timolol across excised human abdominal cadaver skin was measured over a period of 72 h following application of a 40-microns thickness patch containing 5, 10, or 20% (w/v) timolol free base. Amounts of timolol in the patch and skin were also determined at 6, 12, 24, 48, and 72 h after the application of the 20% (w/v) patch. The mean diffusion and partition parameters were estimated to be 0.018 h-1 and 125.9 microns, respectively, using a newly developed theory. Diffusion and partition parameters were estimated using the values for amounts of a drug eventually partitioning into the perfusing water, as well as two newly proposed conceptual parameter values, AUCAv and AUCAs which are the AUCs of drug amounts in vehicle and skin, respectively. The dose-dependent skin-timolol interaction is also discussed.

Determination of some beta-blockers as dabsyl derivatives by HPLC

A HPLC method has been developed that permits the sensitive determination of beta adrenergic blocking drugs, including acebutolol, metoprolol, oxprenolol, pindolol, and propranolol. These compounds were converted to their chromophoric dabsyl derivatives and were separated by a reversed phase chromatographic column (mu-Bondapak C18) with methanol-water (75:25) as isocratic mobile phase. The derivatives were detected by a variable wavelength detector operating at 430 nm. The method was applied to commercial pharmaceutical preparations and the results were statistically compared with those obtained by official methods using t- and F-tests.

Comparative evaluation of cardioselectivity of metoprolol OROS and atenolol: a double-blind, placebo-controlled crossover study

Cardioselectivity of a single oral dose of metoprolol oral osmotic (OROS) (14/190 mg) and atenolol (100 mg) was compared in 12 patients with reversible obstructive airway disease by assessing the dose-response curve to increasing doses of inhaled salbutamol. The beta-blocking activity of the two drugs, which was determined by measuring heart rate, blood pressure, and derived indexes at peak plasma drug levels, was similar. Both metoprolol and atenolol significantly reduced forced vital capacity and peak expiratory flow, with no difference between drugs. Atenolol but not metoprolol also significantly reduced forced expiratory volume in 1 second and specific airway conductance. Both metoprolol and atenolol shifted the dose-response curve of specific airway conductance to the right. The results indicate that the new OROS delivery system for metoprolol, which produces a relatively constant plasma drug level, provides a cardioselectivity comparable to or greater than that of atenolol at maximum plasma levels.

Kinetic determination of sotalol by oxidation with sodium vanadate

A kinetic method is described for the determination of sotalol. The method uses 0.033 M sodium vanadate to oxidize sotalol in 4 M sulphuric acid. The solution is heated at 90 degrees C and the absorbance is measured at 750 nm at a fixed time of 30 min. The concentration (c) of sotalol is calculated from the absorbance (A) by the equation: A = 0.04 + 0.0015625 c.

High-performance liquid chromatographic determination of beta-adrenoceptor blocking agents in body fluids

Several reports have been published reviewing high-performance liquid chromatographic (HPLC) methods for the determination of beta-adrenoceptor blocking agents (beta-blockers) in biological materials (Flouvat et al., 1981; Mehta, 1983; Marko and Soltés, 1984; Ahnoff et al., 1985; Tkaczyková and Safarík, 1987). Of these, the paper by Mehta (1983) briefly summarizes the interrelationship between physiocochemical properties of beta-blockers with prechromatographic treatment of biological samples, as well as with the HPLC methods used for the determination of 12 beta-adrenoceptor blocking drugs. The work by Ahnoff et al. (1985) concerning the monitoring of cardiovascular drugs also deals with HPLC assays of 18 beta-blockers in plasma. The Appendix to this report presents the great majority of HPLC methods for determining 30 beta-blockers in various body fluids. HPLC methods providing resolution and determination of individual beta-blocker enantiomers have not been included since this topic is being covered by Walle and Walle (1989). The Appendix is just a guide to the methods reviewed for the HPLC determination of parent beta-blockers as well as some of their metabolites co-assayed in various body fluids. It does not include details such as the internal standard, recovery, setting of the detector, limit of determination, etc., given in the individual methods listed. The isolation technique of the drug(s) from the given body fluid represents the main step in the sample work-up procedure. Along with this information, only the type of the HPLC column packing and the detection principle used by each method's developers are given.

Effect of diltiazem on the pharmacokinetics of propranolol, metoprolol and atenolol

The pharmacokinetic interaction between diltiazem and three beta-adrenoceptor blockers propranolol, metoprolol and atenolol was investigated in healthy volunteers given diltiazem 30 mg or placebo t.d.s. for 3 days, followed by a single dose of propranolol 20 mg, metoprolol 40 mg or atenolol 50 mg. The AUCs of propranolol and metoprolol were significantly increased after diltiazem and it significantly prolonged the elimination half-life of metoprolol. In contrast, it did not significantly affect the pharmacokinetics of atenolol. Propranolol significantly decreased the resting pulse rate after diltiazem pretreatment as compared to placebo. The results indicate that diltiazem impaired the clearance of propranolol and metoprolol, which are principally metabolized by an oxidative pathway, and that the kinetic interaction between diltiazem and propranolol may partly be related to the significant reduction in the pulse rate produced by the latter.

Foetoplacental drug clearance in the rabbit: studies with trimazosin, acebutolol and tolmesoxide

1. An animal model suitable for studying placental extraction of large numbers of drugs without the need for major surgical facilities, has been developed in the anaesthetized New Zealand white rabbit with sampling of both arterial and venous blood of the foetoplacental unit. 2. Three drugs with different routes of metabolism were studied: trimazosin, tolmesoxide and acebutolol. There was no extraction across the foetoplacental unit. 3. The clearance of acebutolol differed significantly in rabbits from different suppliers. 4. These results do not suggest a role for the placenta in drug metabolism. They do, however, suggest a previously undescribed genetic determinant of acebutolol metabolism.

Liquid chromatographic determination of sotalol in plasma and urine employing solid-phase extraction and fluorescence detection

A liquid chromatographic method using a solid-phase extraction procedure for the quantification of sotalol in plasma and urine is described. Sotalol is eluted from an extraction column with ethyl acetate-acetonitrile (1:2) and, after separation by reversed-phase high-performance liquid chromatography on a mu Bondapak C18 column, is quantified by fluorescence detection at excitation and emission wavelengths of 240 and 310 nm, respectively. The method has been demonstrated to be linear over the concentration ranges 10-6000 ng/ml in plasma and 0.5-100 micrograms/ml in urine. Mean inter-assay accuracy of the method for plasma ranged from 93 to 100% and for urine from 102 to 114%; precision ranged from 0.5 to 1.6% for plasma over a concentration range of 200-4000 ng/ml and for urine from 0.7 to 2.0% at concentrations of 2-50 micrograms/ml. Mass spectrometry confirmed the presence of sotalol in isolated chromatographic fractions of plasma and urine extracts from subjects given sotalol orally.

Adimolol, a long acting beta-adrenoceptor blocker in man

A comparative study in eight healthy normotensive males of the effects on blood pressure, heart rate and beta-adrenoceptor function following single oral doses of adimolol (600 mg), propranolol (240 mg) and placebo. Both active treatments produced small but significant reductions in blood pressure and heart rate, supine and erect. These effects persisted for up to 7 days after adimolol. The heart rate increases following both dynamic exercise and intravenous isoprenaline were attenuated by both propranolol and adimolol. With adimolol evidence of functional beta-adrenoceptor antagonism was sustained for up to 7 days. Lymphocyte beta-adrenoceptor binding studies showed that both adimolol and propranolol significantly reduced affinity for beta-adrenoceptors. In addition, adimolol significantly reduced receptor number and even by 3 days after dosing Bmax had only returned to half the control value. In a small sub-group of subjects there was no evidence to suggest that adimolol had additional alpha-adrenoceptor antagonist properties. Adimolol was detected in plasma for up to 3 days after dosing. The mean terminal elimination half-life was 14 h, compared to 3 h for propranolol. This study confirms that adimolol has prolonged beta-adrenoceptor antagonist activity with effects persisting for up to 7 days after a single dose. The reduction in beta-adrenoceptor number following adimolol suggests that this prolonged effect may not be solely due to competitive antagonism but may additionally depend upon non-competitive antagonism at beta-adrenoceptors.

High-performance liquid chromatographic method for the determination of pindolol in human plasma

A sensitive, simple and highly reliable high-performance liquid chromatographic method using fluorescence detection is reported for the determination of pindolol in plasma. This method involves a single extraction of pindolol from alkalinized plasma into methyl tert.-butyl ether followed by a back-extraction into dilute hydrochloric acid. Injection of the dilute acid phase directly onto an octyl (LC-8) bonded-phase column provides the final separation, and detection of pindolol is achieved by monitoring the intrinsic fluorescence of pindolol at 315 nm following excitation at 255 nm. The method is sensitive enough to measure with confidence pindolol plasma concentrations of 2 ng/ml using a 2-ml sample. No internal standard is required. This method has been applied to the analysis of 1500 human plasma samples by two different laboratories.

Versatile isocratic high-performance liquid chromatographic assay for propranolol and its basic, neutral and acidic metabolites in biological fluids

A comprehensive high-performance liquid chromatographic method was developed for quantitating propranolol and its known metabolites in serum, bile and urine. Analysis was performed before and after incubation of the samples with beta-glucuronidase-arylsulfatase to quantitate both free and conjugate forms of the oxidative metabolites. Fractionation of the basic, neutral and acidic metabolites was achieved by differential pH solvent extraction. The basic and neutral metabolites were extracted from the biological samples at pH 10.5 with 2% n-butanol in dichloromethane. Additional clean-up of the basic fraction by back-extraction into dilute acid was needed for those samples that were subjected to enzymatic hydrolysis. The original aqueous sample was titrated with acid to pH 1, followed by extraction of the remaining acidic metabolites into either n-butanol-dichloromethane (with unhydrolyzed serum) or carbon tetrachloride (with all other samples). Chromatographic separation of the metabolites in the different extracts was achieved on a reversed-phase C18 column, using a single isocratic mobile phase consisting of 0.044 M pH 2.7 phosphate buffer, tetrahydrofuran, methanol and acetonitrile, with the addition of n-butylamine as a competing base to control retention volume and peak shape. Detection and quantitation of propranolol and its metabolites in the low nanogram to sub-nanogram range was afforded by fluorescence at a low UV excitation wavelength. The coefficients of variation for replicate assay of spiked samples were uniformly less than 6% for all the analytes.

Identification and differentiation of beta-blockers and their metabolites in urine by computerized gas chromatography-mass spectrometry

A method for the identification and differentiation of beta-blockers and their metabolites in urine after acid hydrolysis is described. The acetylated extract is analysed by computerized gas chromatography-mass spectrometry. An on-line computer allows rapid detection using ion chromatography with the ions of m/z 72, 86, 98, 140, 151, 159, 200 and 335. The identity of positive signals in the reconstructed ion chromatogram is confirmed by a comparison of the stored entire mass spectra with the reference spectra. The ion chromatogram, the reference mass spectra and the gas chromatographic retention indices (OV-101) are documented. References for the quantitation of the single beta-blockers are cited.

Comparison of the effects of penbutolol and propranolol on glomerular filtration rate in hypertensive patients with impaired renal function

Penbutolol and propranolol were administered orally in a dosage of 40 mg once daily and 80 mg twice daily, respectively to 12 patients with hypertension and impaired renal function. Both drugs caused a significant decrease in mean arterial pressure and heart rate. Serum creatinine concentration increased significantly by 10% during therapy with propranolol without concomitant decrease in creatinine clearance. No such effect was seen with penbutolol. GFR measured with [125I]-iothalamate showed no significant changes with both drugs.

Twenty-four hour effects of oxprenolol Oros and atenolol on heart rate, blood pressure, exercise tolerance and perceived exertion

The effects of oxprenolol, a non-selective beta-blocker with moderate intrinsic sympathomimetic activity (ISA), given by the Oros delivery system, on resting and exercise heart rate and blood pressure have been compared over a 24-h period with those of atenolol, a beta 1-selective blocker without ISA. The effects on maximal and submaximal exercise tolerance and perceived exertion were studied in relation to the level of beta-blockade. 9 healthy subjects were treated with placebo, atenolol, 100 mg/day and oxprenolol Oros, 16/260 mg/day in random order, each for 5 days. Progressive maximal exercise tests and submaximal endurance tests at 80% of maximum aerobic exercise capacity were performed 2, 5 and 24 h after intake of the drugs. The reduction of blood pressure 2 and 5 h after drug intake was less pronounced after oxprenolol Oros than after atenolol, but by 24 h after the last dose the effects were similar. The peak level of beta-blockade (i.e. reduction in maximal exercise heart rate) was similar after oxprenolol Oros and atenolol. The minimal level of beta-blockade 24 h after the last dose was greater after oxprenolol Oros than after atenolol. Maximal exercise capacity and submaximal exercise tolerance were impaired after both beta-blockers. The subjective feeling of exertion did not differ between placebo, atenolol and oxprenolol Oros when related to the relative work load, except after the first minute of exercise, when the rating of perceived exertion was higher after atenolol.

Determination of pindolol in human plasma and urine by high-performance liquid chromatography with ultraviolet detection

This paper presents a rapid, simple and economical method for assaying pindolol concentrations in plasma and urine by high-performance liquid chromatography using ultraviolet detection. It is sensitive enough for use in single-dose pharmacokinetic studies and may also be used to determine pindolol concentrations in the plasma from patients taking the drug, provided that the patient is not taking any of the drugs which interfere with the method. Drugs which were found to interfere with the pindolol peak are quinidine, n-acetylprocainamide and lidocaine. Disopyramide, oxprenolol and levobunolol interfered with the internal standard peak.

Determination of oxprenolol in human plasma by high-performance liquid chromatography, in comparison with gas chromatography and gas chromatography-mass spectrometry

A high-performance liquid chromatographic method for the quantitative assay of oxprenolol in human plasma is described. After addition of alprenolol as internal standard, the compounds are extracted from plasma at alkaline pH into an organic phase and back-extracted into an acidic aqueous phase. Separation of the plasma components and metabolites was achieved on a reversed-phase column. Concentrations down to 66 nmol/l (20 ng/ml) can be determined with UV detection at 222 nm. This technique compares favourably with gas chromatographic and gas chromatographic-mass spectrometric methods.

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.

Acebutolol: ten years of experience

During 10 years of clinical use involving almost 3 million patient-years, acebutolol has become established as a remarkably safe and well-tolerated beta-blocking agent, effective in treating essential hypertension and cardiac arrhythmias. The existence of a long-lived active metabolite (diacetolol) confers a 24-hour duration of action, which permits effective use of a once-daily regimen, particularly for hypertension. Acebutolol has low lipid solubility and low protein binding; the former property reduces the risk of central side effects, and the latter means that displacement interactions with other drugs are unlikely. Because acebutolol and its metabolite normally have both renal and hepatic excretion pathways, an alternative pathway is available should either be compromised through disease. Acebutolol is cardioselective, and clinical use has borne out the low incidence of bronchospasm in patients with impaired lung function. The possession of intrinsic sympathomimetic activity (ISA) leads to only modest reductions in cardiac output, which in turn reduces the chance of excessive bradycardia and the likelihood of precipitating heart failure. A combination of selectivity and ISA may be responsible for the low incidence of tiredness and cold extremities observed with acebutolol compared with other beta blockers. The unique pharmacologic and pharmacokinetic profile of acebutolol confers several therapeutic advantages and may be responsible for the generally low level of side effects experienced in clinical use.

Quantitative determination of tertatolol in biological fluids by gas chromatography-mass spectrometry

Quantitative determination of tertatolol concentrations in plasma and urine was performed by gas chromatography-mass spectrometry in the chemical-ionization mode with ammonia after successive extractions of the beta-blocking drug in alkaline, acid and final alkaline medium. [2H9]Tertatolol, isotopically stable under the operating conditions employed, was used as an internal standard, thus allowing quantities of 1 ng/ml to be specifically determined. Overall analytical error was less than 10%. Prior to isothermal chromatography at 240 degrees C on a column packed with 3% SE-30, both compounds were silylated with bis(trimethylsilyl)trifluoroacetamide. Detection was performed by monitoring the quasimolecular ions of tertatolol, m/z 368 and m/z 377, for the [2H9]tertatolol in the chemical-ionization mode with ammonia. The calibration curves obtained had linear characteristics for the concentration range 1-1125 ng/ml.