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

Clinical Pharmacokinetics of Metoprolol: A Systematic Review

BACKGROUND

Metoprolol is recommended for therapeutic use in multiple cardiovascular conditions, thyroid crisis, and circumscribed choroidal hemangioma. A detailed systematic review on the metoprolol literature would be beneficial to assess all pharmacokinetic parameters in humans and their respective effects on patients with hepatic, renal, and cardiovascular diseases. This review combines all the pharmacokinetic data on metoprolol from various accessible studies, which may assist in clinical decision making.

METHODOLOGY

The Google Scholar and PubMed databases were searched to screen articles associated with the clinical pharmacokinetics of metoprolol. The comprehensive literature search retrieved 41 articles including data on plasma concentration-time profiles after intravenous and oral (immediate-release, controlled-release, slow-release, or extended-release) routes of administration, and at least one pharmacokinetic parameter was reported in all studies included.

RESULTS

Out of 41 retrieved articles, six were after intravenous and 12 were after oral administration in healthy individuals. The oral studies depict a dose-dependent increase in maximum plasma concentration (C_max), time to reach maximum plasma concentration (T_max), and area under the concentration-time curve (AUC). Two studies were conducted in R- and S-enantiomers, in which one study reported the gender differences, depicting greater C_max and AUC among women, whereas in another study S-metoprolol was found to have higher values of C_max, T_max, and AUC in comparison with R-metoprolol. Results in different diseases depicted that after IV administration of 20 mg, patients with renal impairment showed an increase in clearance (CL) (60 L/h vs 48 L/h) compared with healthy subjects, whereas a decrease in CL (36.6 ± 7.8 L/h vs 48 ± 6.6 L/h) was seen in patients with hepatic cirrhosis at a similar dose. In comparison with a single oral dose following administration of 15 mg IV in three divided doses, patients having an acute myocardial infarction (AMI) showed an increase in C_max (823 nmol/L vs 248 nmol/L) at a steady state. Twenty different studies have reported significant changes in CL, C_max, and AUC of metoprolol when it is co-administered with other drugs. One study has reported a drug-food interaction for metoprolol but no significant changes were seen in the C_max and AUC.

CONCLUSION

This review summarizes all the pharmacokinetic parameters of metoprolol after pooling up-to-date data from all the studies available. The summarized pharmacokinetic data presented in this review can assist in developing and evaluating pharmacokinetic models of metoprolol. Moreover, this data can provide practitioners with an insight into dosage adjustments among the diseased populations and can assist in preventing potential adverse drug reactions. This review can also help avoid side effects and drug-drug interactions.

Evaluating the Clinical Impact of Formulation Variability: A Metoprolol Extended-Release Case Study

The objective of this research was to evaluate the impact of changes in the formulation of metoprolol extended-release (ER) tablets on dissolution, pharmacokinetic, and exercise-induced heart rate (EIHR) using a combined physiologically based absorption pharmacokinetic, and population pharmacokinetic/pharmacodynamic modeling and simulation approach. Using a previously developed physiologically based absorption pharmacokinetic model in DDDPlus and GastroPlus, we simulated the changes in drug release and exposure as the result of quantitative changes in the release-controlling excipient, hydroxylpropylmethylcellulose, for 50 and 200 mg. The similarity of dissolution profiles was assessed using the f₂ test, and bioequivalence was tested on the simulated pharmacokinetic profiles. We used the simulated concentration-time profiles following formulation changes as pharmacokinetic input into a population pharmacokinetic/pharmacodynamic model newly developed in NONMEM to determine if changes in pharmacokinetics lead to clinically significant changes in pharmacodynamics. Pharmacodynamic assessment was based on the percentage reduction in the EIHR from baseline. Therapeutic effect was considered similar when the model-predicted EIHR was within 50% to 85% of the average maximum EIHR of healthy 30-year-old subjects. A 40% or more increase in the release rate constant resulted in dissimilarity in dissolution profiles and bioINequivalence in pharmacokinetics for both 50 and 200 mg. Formulation-related differences in drug release of metoprolol ER tablets can lead to differences in pharmacokinetics. However, the evaluated pharmacokinetic differences do not lead to clinically meaningful differences in EIHR, suggesting that EIHR may not be sensitive enough to detect changes in pharmacokinetics of metoprolol ER products.

Pharmacokinetic Variability of Drugs Used for Prophylactic Treatment of Migraine

In this review, we evaluate the variability in the pharmacokinetics of 11 drugs with established prophylactic effects in migraine to facilitate 'personalized medicine' with these drugs. PubMed was searched for 'single-dose' and 'steady-state' pharmacokinetic studies of these 11 drugs. The maximum plasma concentration was reported in 248 single-dose and 115 steady-state pharmacokinetic studies, and the area under the plasma concentration-time curve was reported in 299 single-dose studies and 112 steady-state pharmacokinetic studies. For each study, the coefficient of variation was calculated for maximum plasma concentration and area under the plasma concentration-time curve, and we divided the drug variability into two categories; high variability, coefficient of variation >40%, or low or moderate variability, coefficient of variation <40%. Based on the area under the plasma concentration-time curve in steady-state studies, the following drugs have high pharmacokinetic variability: propranolol in 92% (33/36), metoprolol in 85% (33/39), and amitriptyline in 60% (3/5) of studies. The following drugs have low or moderate variability: atenolol in 100% (2/2), valproate in 100% (15/15), topiramate in 88% (7/8), and naproxen and candesartan in 100% (2/2) of studies. For drugs with low or moderate pharmacokinetic variability, treatment can start without initial titration of doses, whereas titration is used to possibly enhance tolerability of topiramate and amitriptyline. The very high pharmacokinetic variability of metoprolol and propranolol can result in very high plasma concentrations in a small minority of patients, and those drugs should therefore be titrated up from a low initial dose, depending mainly on the occurrence of adverse events.

Impact of norepinephrine and selective β1-adrenoceptor blockers on the growth of retinal tissue explants

We studied the effect of norepinephrine and selective β(1)-adrenoceptor blockers on the growth of retinal tissue explants from 10-12-day-old chicken embryos in organotypic culture. The test drugs produced a dose-dependent effect on cell proliferation. Norepinephrine (10(-12) M) and atenolol (10(-4) M) are shown to significantly stimulate explant growth. Combined treatment with norepinephrine (10(-12) M) and atenolol (10(-4) M) results in cumulation of their stimulatory effects. The results suggest that the retina-stimulating effect of norepinephrine is based on its interactions with other types of adrenoceptors.

Effect of atenolol vs metoprolol succinate on vascular function in patients with hypertension

BACKGROUND

We evaluated the effect of atenolol vs metoprolol succinate on vascular function in patients with essential hypertension.

HYPOTHESIS

Given intrinsic differences between these agents, we hypothesized that atenolol and metoprolol succinate would have disparate effects on vascular function.

METHODS

This study included 24 patients with hypertension (age 56 ± 2 years, 8 female, body mass index 28 ± 1) and featured a randomized, double-blind, crossover design. Each β-blocker (atenolol or metoprolol succinate) was taken by patients once daily for a 4-week period. Measures of vascular function included peripheral augmentation index (AIx) and pulse wave amplitude reactive hyperemia index from peripheral arterial tonometry, and brachial artery flow-mediated dilation from ultrasound.

RESULTS

There were similar reductions in mean arterial pressure following treatment with atenolol and metoprolol succinate. Compared with metoprolol succinate, there was a significant increase in peripheral AIx following atenolol therapy (P < 0.05). There were no changes in brachial artery flow-mediated dilation or pulse wave amplitude reactive hyperemia index following either drug treatment.

CONCLUSIONS

Although atenolol and metoprolol succinate have similar effects on blood-pressure reduction, they have different effects on vascular function. Compared with metoprolol succinate, atenolol increases peripheral AIx. Neither drug has an effect on vascular endothelial function. These findings may have clinical implications, depending on the indication for treatment in an individual patient.

Metoprolol succinate combination in the treatment of hypertension

Metoprolol is a selective beta(1)-adrenergic antagonist extensively used since 1975. Metoprolol has proven its efficacy in reducing cardiovascular events and mortality in patients with hypertension and coronary heart disease. A recently developed controlled release/ extended-release formulation of metoprolol succinate was designed to provide relatively constant metoprolol plasma concentrations and beta(1)-blockade while retaining the convenience of once daily administration. A 100-mg metoprolol controlled/extended-release tablet contains 95 mg of metoprolol succinate and is considered to have equivalent activity of 100 mg metoprolol tartrate. After ingestion, the tablet disintegrates into individual pellets and each pellet acts as a diffusion cell releasing the drug at a relatively constant rate over a period of approximately 20 hours. The aim of this review was to determine the pharmacokinetic and pharmacodynamic properties of metoprolol succinate and to apply those properties in combination with other drugs mainly diuretics in the treatment of hypertension.

Treatment with metoprolol succinate, a selective beta adrenergic blocker, lowers blood pressure without altering insulin sensitivity in diabetic patients

Insulin resistance is a risk factor for cardiovascular disease. Therapies to lower blood pressure should not decrease insulin sensitivity, especially among high-risk patients such as diabetics. This study examined the effect of the beta1-selective adrenergic receptor-blocking agent extended-release metoprolol succinate (ER metoprolol) on insulin sensitivity in type 2 diabetic patients with suboptimal blood pressure control. Diabetic patients with average blood pressure levels >130/85 mm Hg despite antihypertensive therapy had insulin sensitivity quantified by insulin clamp. ER metoprolol was then added to their ongoing therapy. Following 12 weeks of ER metoprolol plus other therapy, the insulin clamp study was repeated. There were no significant changes in measures of insulin sensitivity, plasma lipids, or hemoglobin A1c with use of ER metoprolol. When beta-blocker therapy is considered, it appears that this agent can be used to treat hypertension without adverse effects on insulin sensitivity in patients with type 2 diabetes, at least over the period of time treated.

A population-based analysis of the class effect of beta-blockers after myocardial infarction

BACKGROUND

Long-term treatment with beta-blockers reduces mortality after acute myocardial infarction (AMI). Whether beta-blockers exert a class effect is unknown.

METHODS

We analyzed mortality after AMI in Canadian patients 65 years or older who were discharged from hospital with a diagnosis of AMI from April 1996 to March 2000. Administrative data from Quebec, Ontario, and British Columbia were merged. We compared patients prescribed with metoprolol, acebutolol, or atenolol within 90 days after discharge.

RESULTS

Among 31576 patients, 67% were prescribed with metoprolol, 24% with atenolol, and 9% with acebutolol. Clinical characteristics and proportion of days covered with a beta-blocker prescription were similar across groups. Although controlling for time-dependent covariates representing current use and dosage, as well as for age, sex, congestive heart failure, and several other comorbidities, patients who filled a prescription for acebutolol (hazard ratio 0.71, 95% CI 0.62-0.81) or atenolol (hazard ratio 0.79, 95% CI 0.73-0.87) had significantly lower mortality in comparison with metoprolol.

CONCLUSIONS

The higher mortality observed in patients receiving metoprolol compared with those receiving atenolol or acebutolol challenges the concept of a class effect of beta-blockers for secondary prevention of AMI.

Metoprolol succinate, a selective beta-adrenergic blocker, has no effect on insulin sensitivity

Insulin resistance is a risk factor for cardiovascular disease. Therapies to lower blood pressure should not decrease insulin sensitivity. Some b-adrenergic blocking agents can have an adverse effect on insulin sensitivity. This study examined the effect of extended-release metoprolol succinate on insulin sensitivity. Nondiabetics with hypertension (N=30) were started on (or changed to) hydrochlorothiazide (HCTZ) 12.5 mg daily for 14 days. Patients with blood pressure>140/90 mm Hg while taking HCTZ alone underwent an insulin clamp procedure to quantify insulin sensitivity. Metoprolol succinate treatment was begun at 50 mg daily and titrated to a dose that lowered blood pressure to <140/90 mm Hg. Following 12 weeks of metoprolol succinate plus HCTZ therapy, the insulin clamp procedure was repeated. On metoprolol succinate plus HCTZ treatment, there were no significant changes in insulin clamp measures of insulin sensitivity. Plasma cholesterol and low-density lipoprotein cholesterol decreased significantly on metoprolol succinate plus HCTZ. When b-blocker therapy is considered, metoprolol succinate can be used to treat hypertension without adverse metabolic effects.

beta-Blocker therapy in veterans with asthma or chronic obstructive pulmonary disease

STUDY OBJECTIVES

To determine whether an association exists between health care resource use and beta-blocker therapy in patients with asthma or chronic obstructive pulmonary disease (COPD), and to determine whether any significant differences exist between type of beta-blocker agent administered and resource use.

DESIGN

Retrospective cohort study.

DATA SOURCE

Three Veterans Administration (VA) databases with information from hospitals and clinics in Iowa and Nebraska. Patients. A total of 8390 veterans with a diagnosis of asthma or COPD receiving treatment with a beta-blocker or another cardiovascular agent.

MEASUREMENTS AND MAIN RESULTS

Clinic visits and hospital admissions for asthma or COPD that occurred in 2000-2001 were identified using electronic administrative data files. Analyses were adjusted for comorbidity and patient demographics. Mean patient age was 67 years, and 97% of the patients were men. In unadjusted analyses, patients taking beta-blockers had more hospital admissions, similar inpatient length of stay (LOS), and fewer outpatient clinic visits for asthma or COPD. In adjusted analyses, however, no difference was noted in the odds of hospital admission or in LOS, and patients had fewer clinic visits related to asthma or COPD. The hazard ratio for hospital admission for asthma or COPD during the observation year was similar for patients taking and not taking beta-blockers, and no difference was noted with selective versus nonselective beta-blockers. However, the hospital admission rate was lower with atenolol than metoprolol.

CONCLUSION

Patients taking beta-blockers did not have more hospital admissions or clinic visits for their asthma or COPD than patients not taking these agents. When clinically indicated, beta-blockers-especially atenolol-should be considered for patients with asthma or COPD.

How should COMET influence heart failure practice?

Much clinical experience has led us to assume that the administration of a b-blocker, regardless of dose or frequency, would produce similar mortality benefits in patients with heart failure. The results from the recently published Carvedilol or Metoprolol European Trial (COMET), which found greater benefit of carvedilol than immediate-release metoprolol on mortality, clearly demonstrated this is not true. In heart failure, the COMET results strongly support the use of beta-blockers that have proven effective in large-scale clinical trials. The primary disagreement regarding COMET concerns the explanation of the efficacy difference between the two b-blockers tested. Pharmacodynamic considerations and hemodynamic data from the COMET trial itself suggest there were unequal degrees of b1-blockade between patients receiving carvedilol and immediate-release metoprolol. Failure to achieve a similar degree of b1-receptor blockade in the two groups prevents conclusions regarding the potential incremental benefits of selective versus nonselective adrenergic blockade. Further studies are needed to determine whether there are additional clinical benefits from the inhibition of adrenergic receptors beyond the proven benefits of b1-blockade.

Do β-blockers prolong survival in heart failure only by inhibiting the β1-receptor? A perspective on the results of the COMET trial

Experimental and clinical studies indicate that carvedilol exerts multiple antiadrenergic effects in addition to beta(1)-receptor blockade, but the prognostic importance of these actions has long been debated. This controversy has now been substantially advanced by the results of the recently completed Carvedilol Or Metoprolol European Trial (COMET), which showed that carvedilol (25 mg twice daily) reduced mortality by 17% when compared with metoprolol (50 mg twice daily), P=.0017--a result that was consistent with the differences seen across earlier controlled trials with beta-blockers in survivors of an acute myocardial infarction and in patients with chronic heart failure. Questions have been raised about the interpretation of these findings in view of the fact that the trial did not use the dose or formulation of metoprolol that was shown to prolong life in a placebo-controlled trial (ie, Metoprolol CR/XL [Controlled Release] Randomized Intervention Trial in Heart Failure). Pharmacokinetic and pharmacodynamic analyses, however, indicate that the dosing regimen of metoprolol selected for use in the COMET trial produces a magnitude and time course of beta(1)-blockade during a 24-hour period that is similar to the dose of carvedilol targeted for use in the trial. These analyses suggest that the observed difference in the mortality effects of metoprolol and carvedilol is not related to a difference in the magnitude or time course of their beta(1)-blocking effects but instead reflect antiadrenergic effects of carvedilol in addition to beta(1)-blockade.

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.

Human variability in polymorphic CYP2D6 metabolism: is the kinetic default uncertainty factor adequate?

Human variability in the kinetics of CYP2D6 substrates has been quantified using a database of compounds metabolised extensively (>60%) by this polymorphic enzyme. Published pharmacokinetic studies (after oral and intravenous dosing) in non-phenotyped healthy adults, and phenotyped extensive (EMs), intermediate or slow-extensive (SEMs) and poor metabolisers (PMs) have been analysed using data for parameters that relate primarily to chronic exposure (metabolic and total clearances, area under the plasma concentration time-curve) and primarily to acute exposure (peak concentration). Similar analyses were performed with the available data for subgroups of the population (age, ethnicity and disease). Interindividual differences in kinetics for markers of oral exposure were large for non-phenotyped individuals and for EMs (coefficients of variation were 67-71% for clearances and 54-63% for C(max)), whereas the intravenous data indicated a lower variability (34-38%). Comparisons between EMs, SEMs and PMs revealed an increase in oral internal dose for SEMs and PMs (ratio compared to EMs=3 and 9-12, respectively) associated with lower variability than that for non-phenotyped individuals (coefficients of variation were 32-38% and 30% for SEMs and PMs, respectively). In relation to the uncertainty factors used for risk assessment, most subgroups would not be covered by the kinetic default of 3.16. CYP2D6-related factors necessary to cover 95-99% of each subpopulation ranged from 2.7 to 4.1 in non-phenotyped healthy adults and EMs to 15-18 in PMs and 22-45 in children. An exponential relationship (R(2)=0.8) was found between the extent of CYP2D6 metabolism and the uncertainty factors. The extent of CYP2D6 involvement in the metabolism of a substrate is critical in the estimation of the CYP2D6-related factor. The 3.16 kinetic default factor would cover PMs for substrates for which CYP2D6 was responsible for up to 25% of the metabolism in EMs.

A double-blind comparison of once-daily metoprolol controlled-release and atenolol in the treatment of Chinese patients with mild to moderate hypertension

The efficacy and tolerability of controlled-release metoprolol (metoprolol CR/ZOK), 100-200 mg, and atenolol, 50-100 mg, once daily was compared in Chinese patients with mild to moderate essential hypertension. The study was of a randomized, double-blind, two-way crossover design. The active treatment periods lasted 4 weeks each and were preceded by a 4-week placebo run-in period. The two double-blind phases were separated by a 2-week washout period on placebo. Blood pressures and heart rates were measured at rest in each 2-week visit and during exercise at the end of each treatment period. Twenty-four patients (M/F = 14/10) were valid for efficacy analysis. Their ages ranged from 39 to 68, with a mean of 53.5 years. The rest supine blood pressure and heart rate before active treatment was 160 +/- 15/106 +/- 6 mmHg and 75 +/- 14 beats/min (mean +/- SD), respectively. A responder was defined as exhibiting a supine diastolic blood pressure < or = 90 mmHg or a supine diastolic blood pressure reduction of at least 10% of the baseline level. Both agents had high response rate: 88% and 92% of all patients responded to metoprolol CR/ZOK and atenolol, respectively. Both active treatments considerably reduced resting systolic and diastolic blood pressures and heart rates as compared with baseline (p < 0.001), respectively. With controlled-release metoprolol, a more pronounced beta 1 blockade was obtained than with atenolol, which was expressed as a significant reduction in exercise-induced heart rate at the highest comparable workload compared with placebo (p < 0.05). These findings are compatible with those reported from western populations.

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.