High-performance liquid chromatographic method for the quantitative analysis of the aryloxypropanolamines propranolol, metoprolol and atenolol in plasma and tissue

Chronopharmacology of β-Adrenoceptor-Blocking Drugs: Pharmacokinetic and Pharmacodynamic Studies in Rats

Specific and nonspecific effects and the pharmacokinetic behavior of β-adrenoceptor-blocking drugs of different Iipophilicity (atenolol, bupranolol, carazolol, metoprolol, ox-prenolol, practolol, propranolol, sotalol) were investigated in L-D-synchronized male rats as a function of treatment time. The studies revealed that pharmacodynamic effects on heart rate, cardiac noradrenaline turnover, and motor activity as well as pharmacokinetic parameters of racemic mixtures of β-receptor blockers display temporal variations with more pronounced pharmacological effects and shorter elimination half-lives in the dark span. Studies with the isomers of bupranolol and practolol indicate no stereospecificity in the central depressant effect; the kinetic behavior of, for example, propranolol, however, exhibits stereospecificity. The results demonstrate the importance of circadian rhythms in modifying the effects and kinetics of drugs. These findings may have therapeutic implication in human subjects.

Enhanced bioavailability of atenolol by transdermal administration of the ethylene-vinyl acetate matrix in rabbits

The pharmacokinetics and bioavailability of atenolol, a antihypertensive, were studied to determine the feasibility of enhanced transdermal delivery of atenolol from the ethylene-vinyl acetate (EVA) matrix system containing polyoxyethylene-2-oleyl ether as an enhancer in rabbits. The atenolol-EVA matrix (20 mg/kg) was applied to abdominal skin of rabbits. Blood samples were collected via the femoral artery for 32 h and the plasma concentrations of atenolol were determined by high-performance liquid chromatography. Pharmacokinetic parameters was calculated using Lagran computer program. The area under the curve (AUC) was significantly higher in the enhancer group (12,402+/-3061 ng/ml.h) than that in the control group (8507+/-2092 ng/ml.h), showing about 46% increased bioavailability (P<0.05). The average C(max) was increased in the enhancer group (1361+/-340 ng/ml) compared with the control group (1168+/-293 ng/ml), but not significantly. The T(max) was significantly decreased in the enhancer group (1.3+/-0.36 h) compared with the control group (2.0+/-0.51 h). The elimination time (t(1/2)) and mean residence time were significantly increased in the transdermal group compared with the IV group. The absolute bioavailability was 19.7% in the control group, 28.6% in the enhancer group and 77.4% in the oral administration group compared with IV the group. As the atenolol-EVA matrix containing polyoxyethylene-2-oleyl ether as an enhancer and tributyl citrate as a plasticizer was administered to rabbits via the transdermal routes, the relative AUC% increased about 1.46-fold compared to the control group, showing a relatively constant, sustained blood concentration with minimal fluctuation. The results of this study show that atenolol-EVA matrix could be developed as a transdermal delivery system providing sustained plasma concentration.

A minisensor for the rapid screening of atenolol in pharmaceutical preparations based on surface-stabilized bilayer lipid membranes with incorporated DNA

This work describes an electrochemical technique that is suitable for the rapid and sensitive screening of atenolol based on surface-stabilized bilayer lipid membranes (s-BLMs) composed from egg phosphatidylcholine (PC). The interactions of atenolol with s-BLMs produced electrochemical ion current increases that reproducible appeared within a few seconds after the exposure of the membranes to the drug. The current signal increase was related to the concentration of atenolol in bulk solution in the micromolar range. The present lipid film-based sensor provided fast response (i.e. on the order of a few seconds) to alterations of atenolol concentration (20 to 200 micro M) in electrolyte solution. ssDNA incorporated into s-BLMs can interact with atenolol, and decreased the detection limit of this drug by one order of magnitude. The oligomers used were single stranded deoxyribonucleic acids: thymidylic acid icosanucleotide terminated with a C-16 alkyl chain to assist incorporation into s-BLMs (5'-hexadecyl-deoxythymidylic acid icosanucleotide, dT(20)-C(16)). The electrochemical transduction of the interactions of atenolol with s-BLMs was applied in the determination of these compounds in pharmaceutical preparations by using the present minisensor.

Two reproducible and sensitive liquid chromatographic methods to quantify atenolol and propranolol in human plasma and determination of their associated analytical error functions

Two liquid chromatography (LC) methods with fluorimetric detection have been developed to measure atenolol and propranolol in human plasma. The same 5 microm Nucleosil RP-18 column, extraction procedure and mobile phase (containing acetonitrile, water, triethylamine and phosphoric acid, pH 3) were used. The linearity ranges were 25-800 ng/ml for atenolol and 3.13-100 ng/ml for propranolol. The coefficients of variation for validation assays were lower than 15% at the concentration assayed. The functions of the analytical error were linear: SD (ng/ml)=7.698+0.037C for atenolol and SD (ng/ml)=0.126+0.036C for propranolol.

Involvement of central beta-adrenoceptors in the tachycardia induced by water immersion stress in rats

The purpose of the present study was to investigate whether central beta-adrenoceptors are involved in stress-induced cardiovascular responses in rats. Using a biotelemetry system, blood pressure and heart rate were measured at rest and during stress induced by immersion in 1 cm-deep water. Intracerebroventricular (i.c.v.) injections of a nonselective beta-adrenoceptor antagonist, DL-propranolol (5 or 50 microg), significantly and dose dependently attenuated the tachycardia induced by water immersion stress (drug-induced reduction of tachycardia at 5 min after the start of stress: 61.4 +/- 13.2% for 5 microg, 72.5 +/- 8.2% for 50 microg). The same doses of DL-propranolol had no effect on the resting heart rate. Injection (i.c.v.) of a lower dose (5 microg) of D-propranolol--which has a lower potency as a beta-adrenoceptor antagonist than DL-propranolol, but a similar local anesthetic, membrane-stabilizing activity--did not attenuate the stress-induced tachycardia, although a higher dose (50 microg) did. Intravenous administration of DL-propranolol (5 or 50 microg) significantly attenuated the stress-induced tachycardia (drug-induced reduction of tachycardia at 5 min after the start of stress: 20.0 +/- 7.5% for 5 microg, 42.4 +/- 3.4% for 50 microg). However, the attenuation was much smaller than in the i.c.v. DL-propranolol-injected group. The i.c.v. injection of the 50 microg dose of DL-propranolol significantly augmented both the resting blood pressure and the pressor response to water immersion stress, whereas the lower dose (5 microg) had no effect. The i.c.v. injection of 50 microg D-propranolol also augmented, although not significantly, the resting blood pressure and the pressor response to stress. These results suggest that central beta-adrenoceptors are involved in the tachycardia induced by water immersion stress in rats.

Micellar liquid chromatography: a worthy technique for the determination of beta-antagonists in urine samples

Several beta-antagonists (acebutolol, atenolol, celiprolol, labetalol, metoprolol, nadolol, propranolol) were determined in urine samples with fluorometric detection after direct injection, in less than 15 min, with a micellar mobile phase of 0.1 M sodium dodecyl sulfate (SDS), 15% propanol, and 1% triethylamine at pH 3. The limits of detection (38 criterion) were usually between 3 and 30 ng/mL. The addition of propanol and triethylamine and the reduction of the pH of the mobile phase improved the efficiency of the chromatographic peaks that was rather low in pure micellar eluents. The selection of the composition of the mobile phase was easily performed through the use of an interpretive procedure which considered the retention times and peak shapes of the beta-antagonists in six chromatograms, obtained at varying concentrations of SDS (0.05-0.15 M) and propanol (5-15% v/v). The chromatograms of urine samples from healthy volunteers, which were administered atenolol, metoprolol, and propranolol, showed only one peak for the former drug and several peaks for the other two. These peaks corresponded to the parent drug and metabolites, which indicated the partial and the extensive degradation of metoprolol and propranolol, respectively.

A rapid and sensitive electron-capture gas chromatographic procedure for analysis of metoprolol in rat brain and heart

A procedure for analysis of metoprolol-utilizing extraction followed by derivatization with pentafluoropropionic anhydride and analysis on a gas chromatograph equipped with a fused silica capillary column, an electron-capture detector and a printer/integrator is described. Propranolol was carried through the procedure as internal standard. The pentafluoropropionyl derivative of metoprolol yields a sharp peak on the gas chromatograph, and the structure of the derivative was confirmed using combined gas chromatography-mass spectrometry. The analytical method is linear, sensitive and reproducible and has been applied to analysis of metoprolol in brain and heart from rats treated with metoprolol intraperitoneally. Pretreatment of the rats with the antidepressant desipramine prior to metoprolol administration resulted in a marked increase in levels of metoprolol in both brain and heart, indicating a pharmacokinetic drug-drug interaction between desipramine and metoprolol.

Densitometric determination of metoprolol tartrate in pharmaceutical dosage forms

This paper describes a simple densitometric method for the determination of metroprolol tartrate in tablets and ampoules. After separation on silica gel GF254 plates, using acetone-methanol-triethylamine as the mobile phase for the tablets and acetone-triethylamine for ampoules, the chromatographic zones corresponding to the spots of metoprolol were scanned. Quantitation was performed using a computer-controlled Camag TLC scanner and applying five-point calibration with polynomial regression. The calibration function was established in the ranges 1-28 micrograms for tablets and 1-9 micrograms for ampoules. The results obtained are precise and reproducible, with recovery values of 99.1-99.4%.

A micro liquid chromatographic assay for the determination of plasma-unbound atenolol

An improved high performance liquid chromatographic assay for plasma-unbound atenolol is described. The assay has a wide range (10-5000 ng ml-1) of linearity and a detection limit of 5 ng ml-1 (or 0.1 ng per injection) with acceptable intra- and inter-assay reproducibilities using small volumes of plasma (100 microliters). Following administration of a single dose of atenolol to the rat, nine blood samples were collected over a period of 8 h. These samples were analyzed for atenolol concentrations by a sensitive and specific microbore high performance liquid chromatograph with a photodiode-array detector. This multi-channel detector was used to acquire spectral information on atenolol and demonstrated a superior performance in comparison to all other techniques in that both qualitative and quantitative information were acquired with the system. Because of it sensitivity and applicability to plasma analysis, the assay can be used for pharmacokinetic studies and is valuable in therapeutic drug monitoring.

On the suitability of urethane bonds between the carrier and the drug moiety in poly(ethyleneglycol)-based oligomeric prodrugs

Some poly(ethyleneglycol) derivatives of propranolol were prepared, in which the drug molecule was linked to the oligomeric carrier via urethane bonds in order to study the suitability of this bond as a linkage between the carrier and the drug moiety in oligomeric prodrugs. For comparison purposes also ethanol- and butanol-based prodrugs of propranolol were prepared, with the same linkage between drug and promoiety. The urethane compounds were obtained by condensation via N,N'-carbonyldiimidazole. None of these compounds gave rise to appreciable blood concentrations of propranolol after oral administration, thus suggesting in this particular case, a relative in vivo resistance of urethane bonds towards cleavage.

Knowledge-based system for the automated solid-phase extraction of basic drugs from plasma coupled with their liquid chromatographic determination. Application to the biodetermination of beta-receptor blocking agents

Techniques for the preparation of biological samples are often based nowadays on solid-phase extraction (SPE). The different SPE steps can be performed automatically on disposable extraction cartridges (DECs) by means of a sample processor. A knowledge-based system was developed to facilitate the development of fully automated methods for the solid-phase extraction of relatively hydrophobic basic drugs from plasma, coupled with their determination by high-performance liquid chromatography (HPLC). The DEC filled with 50 mg of cyanopropyl-bonded silica phase is first conditioned with methanol and buffer solution (pH 7.4). After sample application, the DEC sorbent is washed with the same buffer. The analytes are then desorbed with an appropriate eluent and the eluate is finally diluted with the same buffer as used in the HPLC mobile phase before injection. Under these conditions, only three variables are still to be optimized: the composition and volume of the elution solvent and the volume of buffer to be added to the eluate. On the basis of this general strategy, a decision tree providing information about suggested starting conditions and guidelines for the optimization of the three variables was developed and implemented by use of a hypermedia software. This didactic expert system was evaluated using several beta-receptor blocking agents as model compounds and the operating conditions obtained for the automated SPE of these compounds are presented. A method for the determination of propranolol in plasma using the SPE conditions deduced from the knowledge-based system was validated. The absolute recovery of propranolol is ca. 93% and the limit of detection is 1.3 ng ml-1. The mean within-day and between-day reproducibilities are 2.3 and 3.6%, respectively.

Central effects of repeated administration of atenolol and captopril in healthy volunteers

The central effects of atenolol (50 mg tds) and captopril (50 mg tds) ingested for a period of seven days were studied in ten healthy volunteers. A placebo and two active control drugs, methyldopa (250 mg tds) and oxazepam (10 mg), were included in the design. Oxazepam was ingested on the seventh day only, with a placebo being taken on the preceding six days. On the seventh day, central effects of the drugs were tested at 10.00-11.00 h (session 1), immediately before the subjects' last dose of each drug and at 2.5-3.5 h after the final dose of each drug (1330-1430 h, session 2). Performance was assessed using digit symbol substitution, continuous attention, letter cancellation, choice reaction time, finger tapping, immediate and short-term memory, critical flicker fusion and two flash fusion. Subjects assessed their mood and well-being on a series of 12 visual analogue scales. Recordings of the EEG and body sway were carried out. Neither atenolol nor captopril altered performance at any of the skills tested. There were no effects on subjectively assessed alertness or mood with captopril, while atenolol significantly increased wakefulness in session 2 and when the two sessions were meaned. Similarly, captopril did not modify body sway, while with atenolol there was a significant decrease in activity in the frequency range 1.0-2.75 Hz from session 1 to session 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of propranolol, labetalol and clenbuterol in rat brain by high-performance liquid chromatography

A rapid and simple HPLC method for the measurement of adrenergic drugs (propranolol, labetalol and clenbuterol) in rat brain is described. This method was applied to establish if these drugs can pass the blood-brain barrier in prenatal or early post-natal life. The chromatography was performed using a C18 column and a phosphate buffer (pH 3)-acetonitrile (65:35, v/v) mixture. After homogenization of the brain tissue in perchloric acid, the supernatant was buffered at pH 9 and extracted with diethyl ether, followed by back-extraction in sulphuric acid. Recoveries of between 80 and 100% were achieved. The method was found to be accurate (100%) and precise (coefficient of variation around 10%). All three drugs were readily detected in the brain of neonatal rats after peripheral administration. In addition, we demonstrated the presence of propranolol in the fetal brain after maternal administration.

Effects of antihypertensive agents on arterial baroreceptor reflexes in conscious rats

The effects of antihypertensive treatment with four currently used agents (trichlormethiazide, atenolol, nicardipine, and enalapril) on the arterial baroreceptor reflex control of renal sympathetic nerve activity and heart rate were investigated in 45 conscious spontaneously hypertensive rats and 37 age-matched Wistar-Kyoto rats. Antihypertensive agents were administered for 2 weeks beginning at 8 weeks of age to treat and prevent the development of hypertension. Blood pressure was reduced to a similar level (-13 +/- 3 mm Hg, p < 0.05) by each antihypertensive agent. Blood pressure, heart rate, and renal sympathetic nerve activity were recorded in the conscious state during phenylephrine and nitroglycerin ramp infusion. The gain in the baroreceptor reflex was determined from the maximum slope of logistic function curves. Untreated spontaneously hypertensive rats exhibited decreased sensitivity of reflex control of renal sympathetic nerve activity and heart rate (-1.78 +/- 0.07% of control/mm Hg and -2.16 +/- 0.05 beats per minute/mm Hg, respectively) compared with untreated Wistar-Kyoto rats (-3.62 +/- 0.18% of control/mm Hg, p < 0.01, and -3.46 +/- 0.11 beats per minute/mm Hg, p < 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Stereospecific high-performance liquid chromatographic assay of metoprolol

A valid, sensitive high-performance liquid chromatographic technique is reported for the separation of the two enantiomers of metoprolol in human plasma. The procedure involves pre-column derivatization with the homochiral reagent S-(+)-1-(1-naphthyl)ethyl isocyanate. Once formed, the diastereomers are separated using normal-phase high-performance liquid chromatography. Fluorescence detection (220 nm excitation; no emission filter) was utilized, resulting in baseline resolution (Rs greater than 1.5). The peaks corresponding to metoprolol enantiomers were free from interference throughout the examined range of 5-500 ng/ml; accuracy and precision were within approximately 10%. Analysis of a plasma sample collected from a healthy volunteer demonstrated that the assay is applicable to clinical studies.

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.

Stereospecific high-performance liquid chromatographic assay of sotalol in plasma

A convenient high-performance liquid chromatographic (HPLC) assay was developed for determination of sotalol (STL) enantiomers in plasma. Following addition of the internal standard (IS; racemic atenolol), enantiomers of STL and IS were extracted using ethyl acetate. After evaporation of the organic layer, samples were derivatized with a solution of S-(+)-1-(1-naphthyl)ethyl isocyanate (NEIC). The resulting diastereomers were chromatographed with normal-phase HPLC with chloroform:hexane:methanol [65:33:2 (v/v)] as the mobile phase at a flow rate of 2 ml/min. The fluorescence detection wavelength was set at 220 nm for excitation with no emission filter. The suitability of the assay for pharmacokinetic studies was determined by measuring STL enantiomers in the plasma of a healthy subject after administration of a single 160-mg oral, racemic dose of STL.

Investigation of the pindolol-Fe(III) complex and its use in the spectrophotometric determination of pindolol in bulk drug and tablets

It was found that pindolol reacts with Fe(III) chloride producing a green water soluble complex (1:1, v/v) with maximum absorbance at 635 nm. By applying the methods of Sommer and Job [Sommer et al., Folia, tomus XI, Chemia 7, 25, 1970] the conditional stability constant of the complex at pH = 1.70 +/- 0.02 was found to be log K' = 4.95 and the molar absorptivity of the complex to be 206 l mol-1 cm-1. Beer's law was obeyed up to a concentration of 220 mumol l-1 of pindolol. The recoveries were 98-101% (n = 7) and the detection limit was 5 micrograms ml-1. The described method was sufficiently simple, selective and sensitive to be suitable for the rapid and accurate determination of pindolol in tablets.

Central effects of the angiotensin-converting enzyme inhibitor, captopril. I. Performance and subjective assessments of mood

1. Central effects of single doses of captopril (12.5, 25 and 50 mg) were studied in fourteen healthy male subjects. Two placebos and an active control drug, oxazepam (15 mg), were included, together with a single dose of atenolol (100 mg). The drugs were administered double-blind at 11.00 h, and performance and subjective feelings were assessed before and from 1.5-2.5 h and 3.5-4.5 h after ingestion. 2. Performance was assessed using digit symbol substitution, continuous attention, letter cancellation, choice reaction time, finger tapping, immediate and short-term memory, together with critical flicker fusion and two flash fusion. Subjects assessed their mood and well-being on a series of 12 visual analogue scales. 3. Captopril did not impair performance on any of the tests, but improved short-term memory (P less than 0.05) and increased the number of letters cancelled (P less than 0.05). Oxazepam reduced the number of substitutions completed in the digit symbol test (P less than 0.01), accuracy on continuous attention (P less than 0.05), number of letters cancelled (P less than 0.05), and rate of finger tapping (P less than 0.05), and increased choice reaction time (P less than 0.001). Atenolol reduced the rate of finger tapping (P less than 0.05), but increased the number of letters cancelled (P less than 0.05). 4. No effects on mood or on subjective feelings were evident with captopril. Oxazepam reduced subjective alertness (P less than 0.05), and atenolol increased feelings of sleepiness (P less than 0.05). 5. Although these observations suggest that central effects may exist with captopril, no adverse consequences have been established on performance or on subjective assessment of mood. Captopril may, therefore, be an appropriate drug for hypertensive patients engaged in skilled activity.

Investigation of penbutolol-iron (III) complex and its spectrophotometric determination in tablets

It has been established that penbutolol reacts with iron(III) chloride in the presence of ammonium thiocyanate to form a pink complex (2:1) that is soluble in chloroform with a maximum absorbance at 478 nm. By application of the methods of Sommer and Job involving non-equimolar solutions, the conditional stability constant (log k') of the complex at the optimum pH of 1.5 +/- 0.02 and an ionic strength of (mu) 0.14 M, was found to be 5.769. The molar absorptivity at 478 nm was 136 1 mol-1 cm-1 at pH 1.5 +/- 0.02. The validity of Beer's law has been tested in the concentration range 3-18 x 10(-4) M; the relative standard deviation (n = 8) was 1.52-3.21%. The proposed method was found to be suitable for the accurate, simple and rapid analysis of penbutolol in the bulk drug and in tablets.

Oral bioavailability of atenolol

The bioavailability of two formulations of atenolol was compared in an open, randomized crossover study. Each film-coated tablet contained 100 mg of active drug. The plasma concentrations of atenolol were determined using a newly developed and specific high-performance liquid chromatography procedure. The areas under the concentration-time curves (AUC) were calculated, as were pair differences and ratios for individual AUC values and for maximum plasma levels. The latter were determined (Cmax.(m] and calculated (Cmax.(c] at the corresponding time values (tmax.) for test and reference formulations, and were then tested for statistical significance. The 95% confidence limits for both test and reference preparations, taken according to Westlake or Wilcoxon, were found to be 80.0-114.7% for AUC, 80.2-119.9% for Cmax. and 74.5-132.8% for tmax. In terms of pharmacokinetic target criteria, therefore, it can be seen that there were no substantial differences between the two film-coated tablets. The two atenolol preparations, therefore, may be classified as bioequivalent.

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.

A strategy for the determination of beta blockers in plasma using solid-phase extraction in combination with high-performance liquid chromatography

This paper describes a general approach for the therapeutic drug monitoring of 13 different beta blockers in plasma. The chromatographic system contains a cyanopropyl-bonded phase as a stationary phase in combination with a mobile phase composed of acetonitrile and phosphate buffer (pH = 3, mu = 0.05). Two modes of detection are used, namely, UV detection and fluorescence detection. The sample pretreatment is performed with a nitrile-sorbent in combination with methanol-phosphate buffer (pH = 3, mu = 0.05) or with methanol containing 0.1% propylamine as eluent. Acceptable recoveries are obtained for practolol, acebutolol, pindolol, oxprenolol, mepindolol, atenolol, propranolol, prenalterol, alprenolol, metoprolol, sotalol and nadolol. For labetalol, however, the elution recovery has to be improved. Finally, this approach is illustrated by the assay of nadolol in the plasma of patients suffering from hypertension, who had received an oral formulation of the drug.

Determination of atenolol in plasma by dual-column liquid chromatography and fluorimetric detection

A simple and rapid liquid chromatographic method for the determination of atenolol in plasma is described. Plasma proteins were precipitated with zinc sulphate and sodium hydroxide prior to injection onto a precolumn, which was connected to the analytical column by a switching valve. When atenolol was eluted onto the analytical column, the precolumn was cleaned by backflushing to eliminate strongly retained endogenous compounds. The atenolol fluorescence was measured after excitation at 197 nm. The limit of quantitation in plasma was 15 ng/ml. The within-day precision of atenolol was 1.6% at a level of 210 ng/ml, 5.0% at 25 ng/ml and the between-day precision was 3.3% at 50 ng/ml.

Central effects of beta-adrenoceptor antagonists. I--Performance and subjective assessments of mood

1. Central effects of the beta-adrenoceptor antagonists, propranolol (40, 80 and 160 mg) and atenolol (50 and 100 mg) were studied in 12 healthy male subjects. Two placebo ingestions and an active control (oxazepam 15 mg) were included. Single doses were administered double-blind at 11.00 h, and assessments of performance and subjective feelings were made before, 2 h and 4 h after ingestion. 2. Performance was measured using letter cancellation, digit symbol substitution, continuous attention, choice reaction time, finger tapping, short term and immediate memory, critical flicker fusion and two flash fusion. Subjective feelings were assessed using twelve visual-analogue scales. 3. Oxazepam impaired performance at letter cancellation (P less than 0.001), digit symbol substitution (P less than 0.05), continuous attention (P less than 0.001), immediate recall (P less than 0.05) and finger tapping (P less than 0.05), but neither of the beta-adrenoceptor antagonists affected these measures. Propranolol (40 and 160 mg) also impaired short term memory (P less than 0.05), though it was not possible to establish this effect with atenolol. 4. Subjective alertness was reduced by oxazepam (P less than 0.01) and atenolol (P less than 0.05), while propranolol (40 mg) reduced anxiety (P less than 0.01) and propranolol (80 mg) impaired ability to concentrate (P less than 0.05). 5. The results suggest that both lipophilic and hydrophilic antagonists modify the central nervous system, though impairment may be difficult to establish with conventional tests. The observations on memory and alertness suggest that the central effect of beta-adrenoceptor antagonists may be subtle.

Circadian changes in the pharmacokinetics and cardiovascular effects of oral propranolol in healthy subjects

Four subjects were synchronized with activity from 07 to 23 h and were given a single oral dose of 80 mg racemic propranolol at fixed times (08, 14, 20 and 02 h) at weekly intervals. ANOVA revealed significant circadian changes in the peak propranolol concentration (Cmax), with a maximum at 08 h and a minimum at 02 h after drug intake; tmax was not dependent on the circadian phase. The elimination half-life varied significantly with the time of day, being shortest at 08 h (3.3 h) and longest at 20 h (4.9 h). The stereospecificity of the propranolol pharmacokinetics was not dependent on the time of drug intake. No circadian variation was found in the maximum decrease in heart rate, but the time to peak effect was dependent on the time of drug intake; tmax was 2.3 h at 08 h and 7.0 h at 02 h. Thus, the time to peak drug concentration did not coincide with the time to peak effect on heart rate at different times of day. Circadian changes were also found in the systolic blood pressure and in the double product. The results show a significant daily variation in the pharmacokinetics and cardiovascular effects of propranolol. However, chronokinetics cannot explain the circadian changes in the effects of the drug. It is concluded that circadian variation in sympathetic tone and vascular reactivity is mainly responsible for the circadian changes in the effects of propranolol.

Capillary gas chromatographic-mass spectrometric study of the effect of solvents on metoprolol and other aryloxypropanolamines

When metoprolol in methanol was analysed by capillary gas chromatography (GC), an additional peak was observed; mass spectrometry (MS) showed this additional peak to have a molecular weight 12 dalton higher than that of the parent compound. A similar phenomenon was observed with other beta-adrenergic blocking aryloxypropanolamines in methanol or dichloromethane. Capillary GC-MS using deuterated solvents as isotopic markers showed that a methylene group from the solvents was incorporated into the parent molecule. The structure of the observed products and the mechanism of their formation are proposed.

Determination of carazolol in tissues of pigs by high-performance liquid chromatography

A new and sensitive method is described for the determination of the beta-receptor blocker Carazolol, 4-(2-hydroxy-3-isopropylaminopropoxy)-carbazole, in different animal tissues. The procedure comprises extraction of Carazolol from tissue, clean-up by Kieselgel adsorption and high-performance liquid chromatographic separation with fluorimetric detection. The determination limit is 0.48 microgram/kg sample. The method has been verified by measuring Carazolol in liver, kidney and filet of a fattening pig treated with Carazolol before slaughtering.

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.

Chronopharmacokinetics of beta-receptor blocking drugs of different lipophilicity (propranolol, metoprolol, sotalol, atenolol) in plasma and tissues after single and multiple dosing in the rat

Comparative pharmacokinetic studies with the beta-receptor blocking drugs propranolol, metoprolol, sotalol and atenolol, differing greatly in lipophilicity, and their main route of elimination were performed in light-dark-synchronized rats after equimolar single (6 mumoles/kg) or multiple (6 X 6 mumoles/kg) drug application. Drug concentrations were determined in plasma and various target organs of the drugs, e.g. heart, muscle, lung and brain, after drug application in the light period (L) and dark period (D), respectively. After single drug administration pharmacokinetic parameters of all drugs depended on the L and D conditions. Elimination half-lives in plasma and organs were shorter during D than during L. No L-D-differences were found in initial drug concentrations of the hydrophilic drugs sotalol and atenolol. In contrast, C0-values of the lipophilic propranolol in highly perfused organs (muscle, lung, brain) and of metoprolol in muscle tissue were significantly higher in D than in L. No obvious temporal dependency was found in other pharmacokinetic parameters (AUC, plasma clearance, Vd beta) with the exception in Vd beta of propranolol. Due to the different physico-chemical properties of the compounds inter-drug-differences in pharmacokinetic parameters including drug accumulation into lung and brain tissue were observed. Multiple drug dosing abolished the circadian-phase-dependency in the elimination half-lives of the drugs due to an increase in D. Only for the highly lipophilic propranolol half-lives in highly perfused organs were still shorter in D than in L.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of metoprolol and its alpha-hydroxylated metabolite in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method has been developed for the simultaneous determination of metoprolol and its alpha-hydroxylated metabolite in plasma, Metoprolol, alpha-hydroxymetoprolol and alprenolol (internal standard) are extracted from plasma at alkaline pH with diethyl ether-dichloromethane (4:1, v/v) and back-extracted with 0.01 N sulfuric acid. A 100-microliter volume of the acidic extract is injected into the chromatographic system. The compounds are eluted in about 12 min with acetonitrile-acetate buffer (75:25, v/v) on a LiChrosorb RP-8 (5 micron) column. The quantitative determinations are made fluorometrically. Concentrations down to 35 nmol/1 (10 ng/ml) of metoprolol base and 30 nmol/1 (8 ng/ml) of alpha-hydroxymetoprolol base in plasma can be determined with good precision and accuracy.