Pharmacokinetic and biopharmaceutic aspects of once daily treatment with metoprolol CR/ZOK: a review article

Carboxylic Acid Counterions in FDA-Approved Pharmaceutical Salts

Salification is one of the powerful and widely employed approaches to improve the biopharmaceutical properties of drugs. The FDA's eighty-year trajectory of new drug approvals depicts around one-third of the drugs clinically used as their pharmaceutical salts. Among various cationic and anionic counterions used in FDA-approved pharmaceutical salts, the carboxylic acids have significantly contributed. A total of 94 pharmaceutical salts discovered during 1943-2020 comprises carboxylic acids as counterions with a major contribution of acetate, maleate, tartrate, fumarate, and succinate. Hydrocodone tartrate is the first FDA-approved carboxylate salt approved in 1943. Overall, the analysis shows that fifteen carboxylic acid counterions are present in FDA-approved pharmaceutical salts with a major share of acetate (18 drugs). This review provides an account of FDA-approved carboxylate salts from 1939 to 2020. The decade-wise analysis indicates that 1991-2000 contributed a maximum number of carboxylate salts (24) and least (3) in 1939-1950. The technical advantage of carboxylate salts over free-base or other counterions is also discussed. Graphical Abstract.

The effects of three absorption-modifying critical excipients on the in vivo intestinal absorption of six model compounds in rats and dogs

Pharmaceutical excipients that may affect gastrointestinal (GI) drug absorption are called critical pharmaceutical excipients, or absorption-modifying excipients (AMEs) if they act by altering the integrity of the intestinal epithelial cell membrane. Some of these excipients increase intestinal permeability, and subsequently the absorption and bioavailability of the drug. This could have implications for both the assessment of bioequivalence and the efficacy of the absorption-enhancing drug delivery system. The absorption-enhancing effects of AMEs with different mechanisms (chitosan, sodium caprate, sodium dodecyl sulfate (SDS)) have previously been evaluated in the rat single-pass intestinal perfusion (SPIP) model. However, it remains unclear whether these SPIP data are predictive in a more in vivo like model. The same excipients were in this study evaluated in rat and dog intraintestinal bolus models. SDS and chitosan did exert an absorption-enhancing effect in both bolus models, but the effect was substantially lower than those observed in the rat SPIP model. This illustrates the complexity of the AME effects, and indicates that additional GI physiological factors need to be considered in their evaluation. We therefore recommend that AME evaluations obtained in transit-independent, preclinical permeability models (e.g. Ussing, SPIP) should be verified in animal models better able to predict in vivo relevant GI effects, at multiple excipient concentrations.

Pharmacodynamics ofβ-Blockers in Heart Failure: Lessons from the Carvedilol Or Metoprolol European Trial

Heart failure is a growing public health problem in the United States, and the approach to the treatment of heart failure has undergone a radical transformation in the past decade. The use of β-blocker therapy in heart failure patients is now widely recommended, based on evidence from large-scale clinical trials demonstrating that bisoprolol, carvedilol, and extended-release metoprolol succinate significantly reduce morbidity and mortality in patients with heart failure. Although these agents appear to provide similar benefits, the question remains whether pharmacologic differences among them could translate to differences in clinical outcomes. The Carvedilol Or Metoprolol European Trial (COMET) compared nonselective blockade of the β1-/β2-/α1-adrenergic receptors with carvedilol versus selective β1-blockade with immediate-release metoprolol tartrate in patients with chronic heart failure. The trial found that carvedilol significantly reduced all-cause mortality compared with immediate-release metoprolol tartrate, although there were no differences in hospitalizations. Herein we review the pharmacokinetics and pharmacodynamics of metoprolol and carvedilol. In doing so, several issues regarding the design of COMET are identified that could alter the interpretation of the results of this trial. These include the choice of dose and dosage regimen of immediate-release metoprolol tartrate, a dosage form that has never been shown to reduce mortality in patients with heart failure. Additional studies are needed to fully understand whether there are any advantages of selective versus nonselective adrenergic blockade and whether there are any clinically meaningful differences in effectiveness between β-blockers with proven benefit in the management of chronic heart failure. The results of COMET demonstrate that all β-blockers and dosage forms are not interchangeable when prescribed for heart failure. Clinicians should choose only those agents (and dosage forms) that have been proven to reduce mortality in this patient population.

Pharmacokinetics of metoprolol during pregnancy and lactation

The objective of this study was to evaluate the steady-state pharmacokinetics of metoprolol during pregnancy and lactation. Serial plasma, urine, and breast milk concentrations of metoprolol and its metabolite, α-hydroxymetoprolol, were measured over 1 dosing interval in women treated with metoprolol (25-750 mg/day) during early pregnancy (n = 4), mid-pregnancy (n = 14), and late pregnancy (n = 15), as well as postpartum (n = 9) with (n = 4) and without (n = 5) lactation. Subjects were genotyped for CYP2D6 loss-of-function allelic variants. Using paired analysis, mean metoprolol apparent oral clearance was significantly higher in mid-pregnancy (361 ± 223 L/h, n = 5, P < .05) and late pregnancy (568 ± 273 L/h, n = 8, P < .05) compared with ≥3 months postpartum (200 ± 131 and 192 ± 98 L/h, respectively). When the comparison was limited to extensive metabolizers (EMs), metoprolol apparent oral clearance was significantly higher during both mid- and late pregnancy (P < .05). Relative infant exposure to metoprolol through breast milk was <1.0% of maternal weight-adjusted dose (n = 3). Because of the large, pregnancy-induced changes in metoprolol pharmacokinetics, if inadequate clinical responses are encountered, clinicians who prescribe metoprolol during pregnancy should be prepared to make aggressive changes in dosage (dose and frequency) or consider using an alternate beta-blocker.

Drug disposition and modelling before and after gastric bypass: immediate and controlled-release metoprolol formulations

AIMS

The aim of the present study was to evaluate the disposition of metoprolol after oral administration of an immediate and controlled-release formulation before and after Roux-en-Y gastric bypass (RYGB) surgery in the same individuals and to validate a physiologically based pharmacokinetic (PBPK) model for predicting oral bioavailability following RYGB.

METHODS

A single-dose pharmacokinetic study of metoprolol tartrate 200 mg immediate release and controlled release was performed in 14 volunteers before and 6-8 months after RYGB. The observed data were compared with predicted results from the PBPK modelling and simulation of metoprolol tartrate immediate and controlled-release formulation before and after RYGB.

RESULTS

After administration of metoprolol immediate and controlled release, no statistically significant difference in the observed area under the curve (AUC(0-24 h)) was shown, although a tendency towards an increased oral exposure could be observed as the AUC(0-24 h) was 32.4% [95% confidence interval (CI) 1.36, 63.5] and 55.9% (95% CI 5.73, 106) higher following RYGB for the immediate and controlled-release formulation, respectively. This could be explained by surgery-related weight loss and a reduced presystemic biotransformation in the proximal gastrointestinal tract. The PBPK values predicted by modelling and simulation were similar to the observed data, confirming its validity.

CONCLUSIONS

The disposition of metoprolol from an immediate-release and a controlled-release formulation was not significantly altered after RYGB; there was a tendency to an increase, which was also predicted by PBPK modelling and simulation.

Meta-analysis of secure randomised controlled trials of β-blockade to prevent perioperative death in non-cardiac surgery

Background

Current European and American guidelines recommend the perioperative initiation of a course of β-blockers in those at risk of cardiac events undergoing high- or intermediate-risk surgery or vascular surgery. The Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography (DECREASE) family of trials, the bedrock of evidence for this, are no longer secure. We therefore conducted a meta-analysis of randomised controlled trials of β-blockade on perioperative mortality, non-fatal myocardial infarction, stroke and hypotension in non-cardiac surgery using the secure data.

Methods

The randomised controlled trials of initiation of β-blockers before non-cardiac surgery were examined. Primary outcome was all-cause mortality at 30 days or at discharge. The DECREASE trials were separately analysed.

Results

Nine secure trials totalling 10 529 patients, 291 of whom died, met the criteria. Initiation of a course of β-blockers before surgery caused a 27% risk increase in 30-day all-cause mortality (p=0.04). The DECREASE family of studies substantially contradict the meta-analysis of the secure trials on the effect of mortality (p=0.05 for divergence). In the secure trials, β-blockade reduced non-fatal myocardial infarction (RR 0.73, p=0.001) but increased stroke (RR 1.73, p=0.05) and hypotension (RR 1.51, p<0.00001). These results were dominated by one large trial.

Conclusions

Guideline bodies should retract their recommendations based on fictitious data without further delay. This should not be blocked by dispute over allocation of blame. The well-conducted trials indicate a statistically significant 27% increase in mortality from the initiation of perioperative β-blockade that guidelines currently recommend. Any remaining enthusiasts might best channel their energy into a further randomised trial which should be designed carefully and conducted honestly.

Tablet splitting: Product quality assessment of metoprolol succinate extended release tablets

Metoprolol succinate extended release tablets comprise a multiple unit system containing metoprolol succinate in a multitude of controlled release pellets. Each pellet acts as a separate drug delivery unit and is designed to deliver metoprolol continuously over the dosage interval. Despite the flexibility that controlled release pellets may offer, segregation is one of the challenges that commonly occur during tableting for such drug delivery system. Since all commercial metoprolol succinate extended release tablets are scored, they are deemed suitable for splitting. The present study was aimed at utilizing an innovative technology to determine the dose uniformity for split tablets. Four marketed drug products consisting of innovator and generics were evaluated for effect of splitting on weight, assay and content uniformity. Novel analytical tool such as near infrared (NIR) chemical imaging was used to visualize the distribution of metoprolol succinate and functional excipients on the surfaces of the marketed tablets. The non-homogeneous distribution of directly compressed metoprolol succinate beads on the surface of the tablets as well as the split intersection explained the large variation in the split tablets' weight and content uniformity results. The obtained results indicated the usefulness of NIR chemical imaging to determine the need for content uniformity studies for certain split tablets.

Rationale, design, and organization of the PeriOperative ISchemic Evaluation (POISE) trial: a randomized controlled trial of metoprolol versus placebo in patients undergoing noncardiac surgery

BACKGROUND

Noncardiac surgery is associated with significant cardiovascular mortality, morbidity, and cost. Small trials of beta-blockers suggest that they may prevent cardiovascular events in patients undergoing noncardiac surgery, but trial results are inconclusive. We have initiated the POISE trial to definitively establish the effects of beta-blocker therapy in patients undergoing noncardiac surgery.

METHODS

The POISE trial is a blinded, randomized, and controlled trial of controlled-release metoprolol versus placebo in 10000 patients at risk for a perioperative cardiovascular event who are undergoing noncardiac surgery. Patients will receive the study drug 2 to 4 hours before surgery and subsequently for 30 days. The primary outcome is a composite of cardiovascular death, nonfatal myocardial infarction, and nonfatal cardiac arrest at 30 days. Patients will also be followed for events at 1 year.

RESULTS

To date, the POISE trial has recruited >6300 patients in 182 centers in 21 countries. Currently, the patients' mean age is 69 years; 63% are males, 43% have a history of coronary artery disease, 43% have a history of peripheral arterial disease, and 30% have diabetes. Most participants have undergone vascular (42%), intraabdominal (23%), or orthopedic (19%) surgery.

CONCLUSIONS

The POISE trial is a large international trial that will provide a reliable assessment of the effects of beta-blocker therapy in patients undergoing noncardiac surgery.

Extended-release metoprolol succinate in chronic heart failure

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and tolerability of extended-release (ER) metoprolol succinate and its role in the management of chronic heart failure.

DATA SOURCES

A MEDLINE search of English-language literature (1990-October 2002) was conducted using congestive heart failure and metoprolol CR/XL or metoprolol CR/ZOK as search terms to identify pertinent studies.

STUDY SELECTION/DATA EXTRACTION

All of the articles identified from the data sources were evaluated, with priority given to randomized, double-blind, placebo-controlled studies.

DATA SYNTHESIS

ER metoprolol succinate is a controlled-release tablet designed to produce even and consistent beta(1)-blockade throughout the 24-hour dosing interval, with less fluctuation in metoprolol plasma concentrations compared with immediate-release metoprolol. Three randomized, double-blind, placebo-controlled trials have evaluated the efficacy of ER metoprolol succinate in the treatment of patients with chronic heart failure. The MERIT-HF (Metoprolol CR/XL Randomized Intervention Trial in Congestive Heart Failure) study, the largest of these trials and the largest randomized mortality trial with beta-blockers in heart failure to date, demonstrated that ER metoprolol succinate reduced the relative risk of all-cause mortality by 34% versus placebo. Furthermore, the relative risk of the combined endpoint of mortality plus all-cause hospitalizations was reduced by 19% and sudden death was reduced by 41%. The benefits of therapy were evident in various patient subgroups, including elderly patients and those with diabetes mellitus. ER metoprolol succinate was generally well tolerated, with a similar proportion of patients discontinuing therapy due to adverse events relative to placebo (9.8% and 11.7%, respectively).

CONCLUSIONS

ER metoprolol succinate therapy provides substantial mortality and morbidity benefits in patients with New York Heart Association class II and III heart failure who are stabilized on angiotensin-converting enzyme inhibitors and diuretics. ER metoprolol succinate is administered once daily, is well tolerated, and provides consistent beta(1)-blockade over the 24-hour dosing interval.

Pharmacokinetic considerations of formulation: extended-release metoprolol succinate in the treatment of heart failure

Extended-release (ER) metoprolol succinate is a controlled-release formulation designed to deliver metoprolol succinate at a near constant rate for approximately 20 h, independent of food intake and gastrointestinal pH. Once-daily dosing of ER metoprolol succinate 12.5-200 mg produces even plasma concentrations over a 24-h period, without the marked peaks and troughs characteristically observed with the immediate-release (IR) formulation. This leads to consistent beta1-blockade over 24 h, while maintaining cardioselectivity at doses up to 200 mg daily. Pharmacokinetic studies have also been performed in heart failure patients and have demonstrated that ER metoprolol succinate is associated with a more pronounced and even beta1-blockade over a 24-h period than the IR formulation. The efficacy and good tolerability of ER metoprolol succinate in heart failure patients has now been demonstrated in a large-scale clinical trial.

Metoprolol CR/XL in the Treatment of Chronic Heart Failure

Metoprolol CR/XL (metoprolol succinate extended-release tablets) is a beta1-selective agent that improved survival and reduced hospitalization among patients with New York Heart Association class II-IV heart failure in a randomized trial. Metoprolol CR/XL differs from conventional metoprolol tartrate with respect to pharmacokinetic and pharmacodynamic properties that may be clinically important in patients with heart failure. A thorough patient evaluation should be performed to determine optimal dosage and titration of this drug, as with any beta-blocker, and to assess the potential for drug-drug or drug-disease interactions. By applying knowledge of drug-specific characteristics and designing therapy for each individual patient, improvement in patient outcomes can be realized with metoprolol CR/XL.

Lipophilic versus hydrophilic beta(1) blockers and the cardiac sympatho-vagal balance during stress and daily activity in patients after acute myocardial infarction

OBJECTIVE

To compare the effects of a lipophilic and a hydrophilic beta(1) blocker on cardiac sympatho-vagal balance during daytime activity and stress in patients four to six weeks after myocardial infarction.

DESIGN

Randomised, double blind, crossover study comparing the effect of atenolol (50 mg once daily) with metoprolol CR (100 mg once daily) with treatment periods of four weeks.

SETTING

Large teaching hospital.

PATIENTS

50 patients (45 male, 5 female, age range 40 to 75 years), four to six weeks after an acute myocardial infarction.

METHODS

At the end of each treatment period the 24 hour heart rate variability, heart rate variability power spectra during head up tilt and mental stress, baroreflex sensitivity, and exercise performance were evaluated.

RESULTS

During daytime activity and during orthostatic and mental stress, both heart rate and the ratio between the low and high frequency spectral components of the heart rate variability were significantly lower with atenolol. Conversely, there was no difference between treatments in baroreflex sensitivity and resting plasma catecholamines. Exercise duration and peak oxygen consumption did not differ between treatments, but the heart rate during submaximal and peak exercise was significantly lower with atenolol.

CONCLUSIONS

At the doses used in this study, atenolol achieved greater beta(1) adrenergic blockade than metoprolol CR and this was associated with significant inhibition of vagal withdrawal during stress. This suggests that peripheral blockade of beta(1) adrenergic receptors may be more important than central blockade in preventing stress induced vagal withdrawal in patients after myocardial infarction.

Effects of 100 mg of controlled-release metoprolol and 100 mg of atenolol on blood pressure, central nervous system-related symptoms, and general well being

Central nervous system (CNS)-related symptoms and quality of life during treatment with controlled-release (CR) metoprolol and a standard formulation of atenolol were compared in a double-blind crossover study in 60 patients with mild to moderate hypertension. After a 4-week placebo run-in period, each beta 1-adrenoceptor blocker was administered at a dosage of 100 mg once daily for 6 weeks. Quality of life was assessed regularly during the active treatment phases by use of two standardized self-administered questionnaires, the minor symptom evaluation (MSE) profile, and the psychologic general well-being (PGWB) index. Both questionnaires have previously been shown to be effective in detecting CNS symptoms and changes in well being produced by beta-blockers. Blood pressure and heart rate were monitored to assess the antihypertensive efficacy of the two drugs. Metoprolol CR and atenolol produced equivalent, clinically effective reductions in systolic and diastolic blood pressures measured 24 hours after administration. The drugs were found to exert similar effects on general well being, as assessed by the PGWB index, and there were no significant differences between the two treatments with regard to the three dimensions of the MSE profile, contentment, vitality, and sleep. Thus, at equivalent antihypertensive dosages, metoprolol CR and atenolol are clinically comparable with regard to the degree of CNS-related symptoms produced and effects on general well being. Because these agents differ markedly in lipophilicity, other factors, such as beta 1-selectivity/nonselectivity, may be more important determinants of whether these subjective symptoms occur during therapy with beta-blockers.

The pharmacokinetics and pharmacodynamics of metoprolol after conventional and controlled-release administration in combination with hydrochlorothiazide in healthy volunteers

We have studied a controlled-release formulation containing metoprolol 100 mg and hydrochlorothiazide 12.5 mg. We compared the pharmacokinetics of both substances and the pharmacodynamics of metoprolol with those of a conventional combination tablet. The controlled-release formulation gave less variable plasma metoprolol concentrations, Cmax 138 nmol.l-1 and Cmin 74 nmol.l-1, whereas for the conventional formulation the mean Cmax of metoprolol was 629 nmol.l-1 and the Cmin 20 nmol.l-1. Despite lower relative systemic availability (68%) for metoprolol from the controlled-release formulation and a smaller AUC, metoprolol from the controlled-release formulation produced a greater total effect, calculated as the area under the curve of the effect on exercise heart rate vs. time (303 vs. 259%.h; P < 0.05). Hydrochlorothiazide was rapidly absorbed from both formulations and the plasma concentration profiles were almost superimposable. Controlled-release metoprolol with hydrochlorothiazide combines effective beta 1-adrenoceptor blockade for 24 h without affecting the pharmacokinetics of hydrochlorothiazide.

Absence of beneficial effect of intravenous metoprolol given during angioplasty in patients with single-vessel coronary artery disease

In a double-blind, randomized, placebo-controlled trial, the possible anti-ischemic effect of metoprolol during percutaneous transluminal coronary angioplasty was tested. Electrocardiograms, hemodynamics, and metabolism were studied in 27 patients with a stenosis in the left anterior descending coronary artery. Measurements took place before angioplasty, after each of four 1-minute occlusions and 15 minutes after the last balloon deflation. Patients were randomly given placebo or metoprolol (15 mg as a bolus intravenously, followed by an infusion of 0.04 mg/kg/hr). At the end of the procedure, the rate-pressure product had decreased by 15% (NS) and 23% (p = 0.001) in the placebo and metoprolol groups, respectively, mainly due to similar decreases in heart rate. Metoprolol tended to lower chest pain and reduce precordial ST-segment elevation due to angioplasty, but the effects were not statistically significant. Lactate, hypoxanthine, and urate release immediately after deflation was similar in both groups. Metoprolol reduced arterial plasma hypoxanthine throughout the procedure by about 30% (p < or = 0.02 vs. placebo). Thus, intravenous infusion of metoprolol did not significantly attenuate chest pain and ST-segment elevation, and failed to decrease cardiac lactate and oxypurine release. It did, however, reduce arterial hypoxanthine concentrations during angioplasty, possibly indicating that the beta-blocker inhibits extracardiac ATP catabolism.

Novel drug-delivery systems for hypertension

Although novel controlled-release drug-delivery systems have been used in other areas of medicine, their application in the treatment of hypertension has been relatively recent. Biotechnical use of chemical-dispensing systems has been applied to propranolol, clonidine (the transdermal therapeutic system), nifedipine (the gastrointestinal therapeutic system), verapamil (the sodium alginate and spheroidal oral-delivery absorption system), felodipine (the hydrophilic gel principle), metoprolol succinate (the multiple-unit pellet system), and diltiazem (one system comprising sustained-release beads and the other utilizing the patented Geomatrix extended-release system). Oral drug-delivery systems allow antihypertensive agents that previously had to be administered two to four times daily to be administered once each day. Potential disadvantages of the oral controlled-release products include delayed attainment of pharmacodynamic effect, unpredictable or reduced bioavailability, enhanced first-pass hepatic metabolism, dose dumping, sustained toxicity, dosing inflexibility, and increased cost. Potential advantages include reduced dosing frequency, enhanced compliance and convenience, reduced toxicity, stable drug levels, uniform drug effect, and decreased total dose. Although skin reactions are common, the transdermal drug delivery of clonidine provides another innovative approach to supplying transcutaneous, controlled, continuous delivery of drug for 7 days. It is possible that future research will prove that the agents that provide complete 24-hour control may reduce the cardiovascular events associated with the early-morning blood pressure surge. This evolution in antihypertensive therapy to achieve once-daily dosing may prove to be of great value to both physicians and patients in the 1990s.

Controlled release metoprolol formulations. A review of their pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension and ischaemic heart disease

Conventional formulations of metoprolol have become well established in cardiovascular medicine and are particularly useful in the management of hypertension and ischaemic heart disease. Recently developed controlled release metoprolol delivery systems (metoprolol CR/ZOK and metoprolol OROS) were designed to overcome the drug delivery problems of matrix-based sustained release forms by releasing the drug at a relatively constant rate over a 24-hour period, and thus producing sustained and consistent metoprolol plasma concentrations and beta 1-blockade while retaining the convenience of once daily administration. Clinically and statistically significant reductions in blood pressure have been observed with metoprolol CR/ZOK and metoprolol OROS 24 hours after administration in mildly or moderately hypertensive patients. Studies in patients with mild to moderate hypertension have demonstrated that a similar or higher percentage of patients achieved a goal response with metoprolol CR/ZOK compared with matrix-based sustained release formulations of metoprolol, or conventional atenolol or bisoprolol, while metoprolol OROS achieved an equal or greater response rate compared with conventional or matrix-based sustained release metoprolol preparations. In patients with stable effort angina pectoris, once daily administration of metoprolol CR/ZOK provided at least equal antianginal efficacy as conventional metoprolol in divided doses, while metoprolol OROS reduced the mean number of anginal attacks by the same margin as atenolol. Controlled release metoprolol formulations have been well tolerated in clinical trials. Metoprolol CR/ZOK was associated with a similar or lesser degree of adverse effects related to the central nervous system compared with atenolol or long acting propranolol. Metoprolol CR/ZOK also demonstrated less pronounced beta 2-mediated bronchoconstrictor effects than atenolol in asthmatics, and less general fatigue and leg fatigue in healthy subjects. Metoprolol OROS produced less pronounced bronchoconstrictor effects than atenolol, matrix-based sustained release metoprolol or long acting propranolol in patients with asthma or obstructive airways disease, and healthy volunteers. These results are presumably due to the beta 1-selectivity of metoprolol in addition to the relatively low plasma concentrations maintained by metoprolol CR/ZOK and metoprolol OROS, and the avoidance of high peak plasma concentrations with these agents. Despite the relative safety of the controlled release forms of metoprolol, the use of all beta-adrenoceptor antagonists should be avoided in patients with a history of bronchospasm. Thus, controlled release metoprolol formulations offer the potential to maximise the confirmed benefits of this agent in the management of hypertension and angina, by maintaining clinically effective plasma concentrations within a narrow therapeutic range over a 24-hour dose interval.

Controlled release metoprolol. Clinical pharmacokinetic and therapeutic implications

Metoprolol is a relatively beta 1-selective beta-blocker used extensively to treat hypertension and angina and as a prophylaxis after myocardial infarction. Conventional formulations are usually administered twice daily and the drug has a tendency to lose its selectivity of action at higher plasma concentrations. Two controlled release formulations, metoprolol CR and metoprolol 'Oros', have made it possible to achieve sustained beta 1-blockade over an entire 24h period and to minimise the loss of selectivity associated with higher plasma concentrations. The CR formulation has been extensively investigated and is the major subject of this review. The 'Oros' formulation is pharmaceutically different from the CR, yet both produce similar plasma concentration profiles and comparable beta 1-blocking effects. The availability of these preparations occurs at a time when increasingly persuasive data are becoming available on the cardioprotective or coronary preventive action of metoprolol.

Pharmacokinetic and pharmacodynamic properties of controlled release (CR/ZOK) metoprolol in healthy Oriental subjects: a comparison with conventional formulations of metoprolol and atenolol

The steady state pharmacokinetics and pharmacodynamics of metoprolol controlled release tablets 100 mg CR/ZOK, was compared with those of metoprolol conventional tablets 100 mg (CT) and atenolol 50 mg (ATL) in ten healthy Oriental men. The study was of double-blind, cross-over placebo controlled design. The three study drugs and placebo were given in a random order once daily for 4 consecutive days with 1-week wash-out between each period. Treadmill exercise tests were performed and blood samples were obtained at fixed intervals after the fourth dose of each treatment. There was less fluctuation in the plasma level-time profile after CR/ZOK than CT and ATL. Plasma concentrations were significantly higher on CR/ZOK than CT at 24 hours after dosing. The relative bioavailability of CR/ZOK to CT was 69.0%. CR/ZOK achieved relatively more uniform beta-blocking effect over the dose interval. Compared to CT and ATL, the peak effect after CR/ZOK was less pronounced and the beta-blockade after 24 hours more effective.

Pharmacokinetic and pharmacodynamic comparison of metoprolol CR/ZOK once daily with conventional tablets once daily and in divided doses

Four studies of identical design, each on 18 young healthy subjects, were undertaken to study the pharmacokinetics and beta 1-receptor blockade at steady state after a once daily dose (od) of 100, 200, 300 and 400 mg of metoprolol CR/ZOK (a new controlled release preparation) in comparison with 100 mg dosages (od, bid, tid and qid, respectively) of conventional metoprolol tablets (CT). All studies were of randomized three-way crossover design with 7-day double-blind treatment periods separated by 7-day single-blind washout periods. A number of predose plasma concentrations and assessments of beta 1-blockade were made during the study and a full pharmacokinetic and pharmacodynamic study was performed on day 7. The maximal plasma concentration, Cmax, was significantly lower after metoprolol CR/ZOK compared to CT after all doses--the most pronounced difference being observed after the 100 mg dose when both preparations were given once daily (145 nmol/L vs 606 nmol/L) and the least difference after the 400 mg dose when metoprolol CT was given every 6 hours (837 nmol/L vs 1111 nmol/L). The maximal plasma concentration occurred later after metoprolol CR/ZOK than CT in all studies (median 2.5-4.1 hours vs 1.0-1.2 hours). The trough plasma concentration, Cmin, was significantly higher after 100 mg metoprolol CR/ZOK compared to CT dosed once daily; CminS were comparable between the two preparations in the 200 mg and 300 mg studies and lower after metoprolol CR/ZOK in the 400 mg study (278 nmol/L vs 469 nmol/L). In all four studies the AUCs were significantly lower after metoprolol CR/ZOK compared to CT with the mean relative bioavailability being approximately similar (73-84%). All metoprolol treatments produced a statistically significant beta 1-blockade (measured as percent reduction of exercise induced tachycardia) throughout the whole day compared to placebo except in the 100 mg study where the effect of once daily CT did not differ from placebo during the last 6 hours. Consequently, a significantly higher beta 1-blockade was observed after metoprolol CR/ZOK compared to CT in this latter period. The maximum beta 1-blockade (Emax) after CR/ZOK 100 mg was significantly lower than after CT 100 mg once daily (12.6% vs 23.3%) but when CT was given in divided doses from 200 to 400 mg daily, Emax did not differ between the two formulations. Once daily administration of 100 mg of both products resulted in a significantly higher beta 1-blockade 24 hours after dosing with CR/ZOK compared to CT, but when CT was taken in divided doses this difference between the treatments was less pronounced.(ABSTRACT TRUNCATED AT 400 WORDS)