The effect of age on the pharmacokinetics of metoprolol and its metabolites

Differential Effects of the Betablockers Carvedilol, Metoprolol and Bisoprolol on Cardiac Kv4.3 (Ito) Channel Isoforms

Cardiac Kv4.3 channels contribute to the transient outward K+ current, Ito, during early repolarization of the cardiac action potential. Two different isoforms of Kv4.3 are present in the human ventricle and exhibit differential remodeling in heart failure (HF). Cardioselective betablockers are a cornerstone of HF with reduced ejection fraction therapy as well as ventricular arrhythmia treatment. In this study we examined pharmacological effects of betablockers on both Kv4.3 isoforms to explore their potential for isoform-specific therapy. Kv4.3 isoforms were expressed in Xenopus laevis oocytes and incubated with the respective betablockers. Dose-dependency and biophysical characteristics were examined. HEK 293T-cells were transfected with the two Kv4.3 isoforms and analyzed with Western blots. Carvedilol (100 µM) blocked Kv4.3 L by 77 ± 2% and Kv4.3 S by 67 ± 6%, respectively. Metoprolol (100 µM) was less effective with inhibition of 37 ± 3% (Kv4.3 L) and 35 ± 4% (Kv4.3 S). Bisoprolol showed no inhibitory effect. Current reduction was not caused by changes in Kv4.3 protein expression. Carvedilol inhibited Kv4.3 channels at physiologically relevant concentrations, affecting both isoforms. Metoprolol showed a weaker blocking effect and bisoprolol did not exert an effect on Kv4.3. Blockade of repolarizing Kv4.3 channels by carvedilol and metoprolol extend their pharmacological mechanism of action, potentially contributing beneficial antiarrhythmic effects in normal and failing hearts.

Pharmacokinetic determinants for the right dose of antiarrhythmic drugs

INTRODUCTION

Antiarrhythmic drugs (AADs) show a narrow therapeutic range and marked intersubject variability in pharmacokinetics (PK), which may lead to inappropriate dosing and drug toxicity.

AREAS COVERED

The aim of the present review is to describe PK properties of AADs, discussing the main changes in different clinical scenarios, such as the elderly and patients with obese, chronic kidney, liver, and cardiac disease, in order to guide their right prescription in clinical practice.

EXPERT OPINION

There are few data about PK properties of AADs in a special population or challenging clinical setting. The use and dose of AADs is commonly based on physicians' clinical experience observing the clinical effects rather than being personalized on the individual patients PK profiles. More and updated studies are needed to validate a patient centered approach in the pharmacological treatment of arrhythmias based on patients' clinical features, including pharmacogenomics, and AAD pharmacokinetics.

Identifying drug-related attributes to personalise antihypertensive agents: the outcome report of patients receiving metoprolol therapy

Background

Currently, numerous antihypertensive drugs from different pharmacological classes are available; however, blood pressure control is achieved in only less than a third of patients treated for hypertension. Moreover, providing optimal and personalised treatment for hypertension is challenging. Therefore, in this study, we propose a ‘drug-related attributes’ sensitive spectrum. This novel concept can assist clinicians in selecting an optimal antihypertensive drug and improve blood pressure control after examining the attributes of a patient.

Methods

We collected clinical data on attributes related to hypertension and its therapy of inpatients from West China Hospital who received metoprolol therapy and constructed the sensitive spectrum using data-visualisation tools.

Results

Our analysis revealed that haematocrit, haemoglobin, serum creatinine, serum cystatin C, serum urea, age, sex, systolic pressure, diastolic pressure, pulse pressure, and heart rate are metoprolol-related attributes.

Conclusion

Our study showed that all metoprolol-related attributes identified are reasonable and helpful in improving the personalisation of metoprolol therapy. The proposed drug-related attributes spectrum can help personalise antihypertensive medication. Moreover, data-visualisation tools can be effectively used to mine the drug-related attributes sensitive spectrum.

Physiologically Based Pharmacokinetic Modelling to Identify Pharmacokinetic Parameters Driving Drug Exposure Changes in the Elderly

BACKGROUND

Medication use is highly prevalent with advanced age, but clinical studies are rarely conducted in the elderly, leading to limited knowledge regarding age-related pharmacokinetic changes.

OBJECTIVE

The objective of this study was to investigate which pharmacokinetic parameters determine drug exposure changes in the elderly by conducting virtual clinical trials for ten drugs (midazolam, metoprolol, lisinopril, amlodipine, rivaroxaban, repaglinide, atorvastatin, rosuvastatin, clarithromycin and rifampicin) using our physiologically based pharmacokinetic (PBPK) framework.

METHODS

PBPK models for all ten drugs were developed in young adults (20-50 years) following the best practice approach, before predicting pharmacokinetics in the elderly (≥ 65 years) without any modification of drug parameters. A descriptive relationship between age and each investigated pharmacokinetic parameter (peak concentration [C_max], time to C_max [t_max], area under the curve [AUC], clearance, volume of distribution, elimination-half-life) was derived using the final PBPK models, and verified with independent clinically observed data from 52 drugs.

RESULTS

The age-related changes in drug exposure were successfully simulated for all ten drugs. Pharmacokinetic parameters were predicted within 1.25-fold (70%), 1.5-fold (86%) and 2-fold (100%) of clinical data. AUC increased progressively by 0.9% per year throughout adulthood from the age of 20 years, which was explained by decreased clearance, while C_max, t_max and volume of distribution were not affected by human aging. Additional clinical data of 52 drugs were contained within the estimated variability of the established age-dependent correlations for each pharmacokinetic parameter.

CONCLUSION

The progressive decrease in hepatic and renal blood flow, as well as glomerular filtration, rate led to a reduced clearance driving exposure changes in the healthy elderly, independent of the drug.

Development and Validation of RP-HPLC and an Ecofriendly HPTLC Method for Simultaneous Determination of Felodipine and Metoprolol Succinate, and their Major Metabolites in Human Spiked Plasma

BACKGROUND

Felodipine is a calcium channel blocker used together with metoprolol succinate for treatment of hypertension.

OBJECTIVE

Two chromatographic methods were developed for simultaneous determination of felodipine (FEL) and metoprolol succinate (MET), and their major metabolites, dehydrofelodipine and metoprolol acid, respectively.

METHODS

The first method was RP-HPLC which comprised separation of the studied components by gradient elution using a Phenomenex C8 column and a mobile phase composed of water (adjusted to pH 3.5 with o-phosphoric acid)-acetonitrile - methanol (45:40:15, by volume) for the first 6 min and (30:60:10, by volume) for the next 4 min at a flow rate of 1 mL/min followed by UV detection of the eluted peaks at 225 nm. The second method was an HPTLC method where separation was achieved using a mobile phase consisting of toluene-ethyl acetate-methanol-ammonia-formic acid (10:5:2.5:0.3:0.1, by volume) and scanning of the separated bands at 225 nm.

RESULTS

Validation of the developed methods was done according to ICH guidelines. Successful application of the developed methods was carried out for determination of the studied drugs in human spiked plasma and in Logimax® tablets.

CONCLUSIONS

The developed RP-HPLC and HPTLC methods can be further applied for quality control testing of the studied drugs.

HIGHLIGHTS

RP-HPLC and HPTLC methods for determination of FEL, MET and their major metabolites. The developed methods were successfully applied for determination of FEL and MET in Logimax® tablets.

Flunarizine as prophylaxis for episodic migraine: a systematic review with meta-analysis

Based on few clinical trials, flunarizine is considered a first-line prophylactic treatment for migraine in several guidelines. In this meta-analysis, we examined the pooled evidence for its effectiveness, tolerability, and safety. Prospective randomized controlled trials of flunarizine as a prophylaxis against migraine were identified from a systematic literature search, and risk of bias was assessed for all included studies. Reduction in mean attack frequency was estimated by calculating the mean difference (MD), and a series of secondary outcomes-including adverse events (AEs)-were also analyzed. The database search yielded 879 unique records. Twenty-five studies were included in data synthesis. We scored 31/175 risk of bias items as "high," with attrition as the most frequent bias. A pooled analysis estimated that flunarizine reduces the headache frequency by 0.4 attacks per 4 weeks compared with placebo (5 trials, 249 participants: MD -0.44; 95% confidence interval -0.61 to -0.26). Analysis also revealed that the effectiveness of flunarizine prophylaxis is comparable with that of propranolol (7 trials, 1151 participants, MD -0.08; 95% confidence interval -0.34 to 0.18). Flunarizine also seems to be effective in children. The most frequent AEs were sedation and weight increase. Meta-analyses were robust and homogenous, although several of the included trials potentially suffered from high risk of bias. Unfortunately, reporting of AEs was inconsistent and limited. In conclusion, pooled analysis of data from partially outdated trials shows that 10-mg flunarizine per day is effective and well tolerated in treating episodic migraine-supporting current guideline recommendations.

Pharmacokinetic and pharmacodynamic considerations in the treatment of the elderly patient with hypertension

INTRODUCTION

Hypertension is an important risk factor for developing cardiovascular diseases. It is more prevalent in the elderly population. Recently updated American and European guidelines recommend treating every elderly patient with hypertension independent of age, starting with a low dose of antihypertensive drugs. However, little information is available on the optimal dosages of antihypertensive drugs to treat the elderly safely. Areas covered: Comorbidities, co-medication and frailty status can alter the clinical outcome of drug treatment and can cause adverse events in the elderly. Also, due to pharmacokinetic and pharmacodynamic changes the interpatient variability when using antihypertensive drugs is considerable. In this review, an overview is given on the extent to which the previously mentioned parameters are changed in elderly patients and what this means for the exposure to antihypertensive medication. Also, recommendations on the starting dose of the most frequently used antihypertensive drugs are given based on literature data. Expert opinion: We believe that recommendations on starting dosages followed by a stepwise increase of dosages will lead to improved blood pressure control and less adverse drug reactions in the elderly patient. This may improve adherence to antihypertensive therapy.

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.

Analysis of the variability of the pharmacokinetics of multiple drugs in young adult and elderly subjects and its implications for acceptable daily exposures and cleaning validation limits

The elderly constitute a significant, potentially sensitive, subpopulation within the general population, which must be taken into account when performing risk assessments including determining an acceptable daily exposure (ADE) for the purpose of a cleaning validation. Known differences in the pharmacokinetics of drugs between young adults (who are typically the subjects recruited into clinical trials) and the elderly are potential contributors affecting the interindividual uncertainty factor (UF_H) component of the ADE calculation. The UF_H values were calculated for 206 drugs for young adult and elderly groups separately and combined (with the elderly assumed to be a sensitive subpopulation) from published studies where the pharmacokinetics of the young adult and elderly groups were directly compared. Based on the analysis presented here, it is recommended to use a default UF_H value of 10 for worker populations (which are assumed to be approximately equivalent to the young adult groups) where no supporting pharmacokinetic data exist, while it is recommended to use a default UF_H value of 15 for the general population, to take the elderly into consideration when calculating ADE values. The underlying reasons for the large differences between the exposures in the young adult and elderly subjects for the 10 compounds which show the greatest separation are different in almost every case, involving the OCT2 transporter, glucuronidation, hydrolysis, CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP3A4 or CYP3A5. Therefore, there is no consistent underlying mechanism which appears responsible for the largest differences in pharmacokinetic parameters between young adult and elderly subjects.

Simultaneous determination of metoprolol and its metabolites, α-hydroxymetoprolol and O-desmethylmetoprolol, in human plasma by liquid chromatography with tandem mass spectrometry: Application to the pharmacokinetics of metoprolol associated with CYP2D6 genotypes

A rapid and simple LC with MS/MS method for the simultaneous determination of metoprolol and its two CYP2D6-derived metabolites, α-hydroxy- and O-desmethylmetoprolol, in human plasma was established. Metoprolol (MET), its two metabolites, and the internal standard chlorpropamide were extracted from plasma (50 μL) using ethyl acetate. Chromatographic separation was performed on a Luna CN column with an isocratic mobile phase consisting of distilled water and methanol containing 0.1% formic acid (60:40, v/v) at a flow rate of 0.3 mL/min. The total run time was 3.0 min per sample. Mass spectrometric detection was conducted by ESI in positive ion selected-reaction monitoring mode. The linear ranges of concentration for MET, α-hydroxymetoprolol, and O-desmethylmetoprolol were 2-1000, 2-500, and 2-500 ng/mL, respectively, with a lower limit of quantification of 2 ng/mL for all analytes. The coefficient of variation for the assay's precision was ≤ 13.2%, and the accuracy was 89.1-110%. All analytes were stable under various storage and handling conditions and no relevant cross-talk and matrix effect were observed. Finally, this method was successfully applied to assess the influence of CYP2D6 genotypes on the pharmacokinetics of MET after oral administration of 100 mg to healthy Korean volunteers.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Quantitative assessment of time dependent drug-use trends by the analysis of drugs and related metabolites in raw sewage

BACKGROUND

Accurate and timely information on the scale and dynamics of drug consumption is important for assessing the needs of law enforcement and public health services in a community.

AIMS

This paper presents a detailed examination of a comprehensive sewage-sampling campaign for the purposes of increasing an understanding of the dynamics of drug-flows in sewage streams, and developing new methodology by which this technique can support traditional drug-use surveys.

METHODS

A total of 104 sewage samples were collected from a treatment plant servicing approximately 500000 people and analysed for levels of methamphetamine, cocaine and cocaine metabolites. Careful examination of the kinetics of drug-flow profiles was then performed in order to identify trends or patterns of use within the community.

RESULTS

Results were validated against identical measurements of pharmaceutical reference compounds. Consumption profiles for cocaine and methamphetamine were found to differ in terms of frequency and timing of use. The majority of cocaine consumption occurs during the evening hours and 45% of consumption of this drug occurs in weekend periods. The flow of methamphetamine in the sewage system appears more evenly spread throughout the week.

CONCLUSIONS

This result is consistent with both an extended excretion half-life and a pattern of use that is more evenly balanced across all days of the week. Comprehensive investigation in to the scale and kinetics of drug flow in a sewage stream can therefore provide valuable information, not only in terms of the volume of drug consumed, but also in terms of identifying differing usage-patterns over daily and weekly time-scales.

Effect of Amiodarone on the Serum Concentration/Dose Ratio of Metoprolol in Patients with Cardiac Arrhythmia

Amiodarone has pharmacokinetic interactions with a number of therapeutic drugs, including warfarin, phenytoin, flecainide, and cyclosporine. Metoprolol is mainly metabolized by CYP2D6, and desethylamiodarone, a metabolite of amiodarone, has a markedly greater inhibitory effect on CYP2D6 than amiodarone. Therefore, the goal of this study was to evaluate the effect of amiodarone and desethylamiodarone on the serum concentration/dose ratio (C/D) of metoprolol in 120 inpatients with cardiac arrhythmias that received either metoprolol and amiodarone (MET+AMD group, n=30) or metoprolol alone (MET group, n=90). The ratio of administered metoprolol was compared between the MET and the MET+AMD groups. The dose of metoprolol and patient age were significantly higher in the MET group when compared with the MET+AMD group (1.00+/-0.480 versus 0.767+/-0.418 mg/kg/day, p<0.050; 68.6+/-10.6 versus 57.6+/-14.1 years, p<0.001, respectively), but the C/D ratio was significantly lower in the MET group than in the MET+AMD group (90.8+/-64.0 versus 136+/-97.8, p<0.01). Furthermore, a significant correlation was found between the C/D ratio and desethylamiodarone concentration (n=30, r=0.371, p<0.01). The results suggest that there is a significant interaction between amiodarone and metoprolol via desethylamiodarone-induced inhibition of CYP2D6. Therefore, careful monitoring of metoprolol concentrations/bioactivity of CYP2D6 is required in the context of co-administration of amiodarone and metoprolol.

Cardiovascular Drug Therapy in Elderly Patients

An increasing number of elderly patients are exposed to cardiovascular drugs for the treatment of acute and/or chronic conditions. This is a result of the progressive aging of the population, a common feature in most industrialised countries, and an improvement in primary and secondary cardiovascular prevention strategies with increased survival rates. Traditionally, most elderly patients receiving cardiovascular drugs had advanced cardiac, liver and kidney disease that significantly influenced drug pharmacokinetic and pharmacodynamic parameters. Currently, however, many patients without significant organ impairment receive cardiovascular therapy for primary or early secondary prevention (i.e. increased vascular risk, asymptomatic left ventricular dysfunction, poststroke phase, type 2 diabetes mellitus), highlighting the need for a better understanding of specific age-related pharmacokinetic and pharmacodynamic effects. A systematic review has been conducted on the specific effects of aging, in the absence of major co-morbidities, on the pharmacokinetic and pharmacodynamic properties of traditional and newer cardiovascular drugs. Currently, the evidence available is poor or nonexisting for several drugs and mainly derived from very small and underpowered studies, thus limiting data interpretation. In particular, there is very little information on patients >80 years of age, thus raising important concerns about the correct use of these drugs in this constantly growing population.

The influence of first pass metabolism on the development and validation of an IVIVC for metoprolol extended release tablets

To investigate the influence of alpha-hydroxymetoprolol (AHM) and 4-(2-hydroxy-3-isopropylaminopropoxy)-phenylacetic acid (ACMB), both derived from its first pass metabolism of metoprolol, an in vitro in vivo correlation incorporating first pass metabolite data for metoprolol extended release formulations was developed. Three different releasing formulations (slow (S), moderate (M) and fast (F), 100 mg) of metoprolol were evaluated in a previously reported clinical study. The non-first pass effect (Non-FPE) in vitro in vivo correlation (IVIVC) was developed using a fraction of metoprolol dissolved and a fraction of total drug (metoprolol + metabolites) as the absorption data for various combinations of formulations (S/M/F, M/F, S/M, and S/F). Direct convolution approaches predicting metoprolol concentrations and indirect convolution predicting total drug concentrations (metoprolol + metabolites) were used to determine in vivo behavior. The Non-FPE IVIVC using the S/M/F formulations displayed the strongest relationship (r2 > 0.92). The IVIVC using the indirect approach was predictive of both the C(max) (prediction errors (PE) 4.77, 3.94 and 6.14%) and AUC (10.7, 11.0 and 11.3%) for metoprolol, AHM and ACMB. Poor predictability (PE > 40% for C(max) and AUC) was observed for metoprolol when using the direct methods. The predictability of the IVIVC using the indirect approach as compared to the direct method displays the influence of first pass metabolism on the development and evaluation of an IVIVC for a drug that displays a high extraction ratio. In addition, the indirect IVIVC allows for not only predicting the in vivo performance of the parent drug but also the metabolites formed via the first pass effect.

Pharmacokinetics of metoprolol enantiomers following single and multiple administration of racemate in rat

The chiral beta-adrenergic blocking agent metoprolol (MET), which is marketed as a racemate, is a highly extracted drug with rapid absorption. The enantiomeric disposition of MET is reported following racemic administration as a single and as multiple oral dosing four times per day for four days in male Sprague-Dawley rats (n=6 in each group). Plasma was collected and enantiomeric concentrations of MET were determined using a stereospecific HPLC assay. The R/S ratio for AUC is not statistically different from unity either after single or after multiple administration of racemate. The oral clearance after single dose was 1.99+/-0.87 and 2. 26+/-0.85 ml min(-1) kg(-1) for R- and S-MET, respectively. These values were decreased to 0.59+/-0.21 and 0.64+/-0.26 ml min(-1) kg(-1) after multiple administration of racemate. The corresponding values for the elimination half-lives were approximately 35 and 33 min after single and multiple dose administration for both enantiomers, respectively. These results may suggest a saturable first pass metabolism of MET as its enantiomers are accumulated in plasma following multiple dosing in the rat model.

Quantitative prediction of in vivo drug clearance and drug interactions from in vitro data on metabolism, together with binding and transport

It is of great importance to predict in vivo pharmacokinetics in humans based on in vitro data. We summarize recent findings of the quantitative prediction of the hepatic metabolic clearance from in vitro studies using human liver microsomes, hepatocytes, or P450 isozyme recombinant systems. Furthermore, we propose a method to predict pharmacokinetic alterations caused by drug-drug interactions that is based on in vitro metabolic inhibition studies using human liver microsomes or human enzyme expression systems. Although we attempt to avoid the false negative prediction, the inhibitory effect was underestimated in some cases, indicating the possible contribution of the active transport into hepatocytes and/or interactions at the processes other than the hepatic metabolism, such as the metabolism and transport processes during gastrointestinal absorption.

Prediction of in vivo drug metabolism in the human liver from in vitro metabolism data

As a new approach to predicting in vivo drug metabolism in humans, scaling of in vivo metabolic clearance from in vitro data obtained using human liver microsomes or hepatocytes is described in this review, based on the large number of literature data. Successful predictions were obtained for verapamil, loxtidine (lavoltidine), diazepam, lidocaine, phenacetin and some other compounds where CLint,in vitro is comparable with CLint,in vivo. On the other hand, for some metabolic reactions, differences in CLint,in vitro and CLint,in vivo greater than 5-fold were observed. The following factors are considered to be the cause of the differences: (1) metabolism in tissues other than liver, (2) incorrect assumption of rapid equilibrium of drugs between blood and hepatocytes, (3) presence of active transport through the sinusoidal membrane, and (4) interindividual variability. Furthermore, the possibility of predicting in vivo drug metabolic clearance from results obtained using a recombinant system of human P450 isozyme was described for a model compound, YM796, where the predicted metabolic clearances obtained from the recombinant system, taking account of the content of the P450 isozyme CYP3A4 in the human microsomes, were comparable with the observed clearances using human liver microsomes containing different amounts of CYP3A4. Even in the case where the first-pass metabolism exhibits nonlinearity, it appears to be possible to predict in vivo metabolic clearance from in vitro metabolic data.

Approaches to meeting the criteria for fixed dose antihypertensive combinations. Focus on metoprolol

Fixed dose antihypertensive combinations are being used increasingly in the management of hypertension. There are advantages and disadvantages of this form of therapy. The key aims are to: (i) achieve increased efficacy by using drugs that complement each other's actions; (ii) use low doses to minimise adverse effects; and (iii) provide a simple once daily regimen. Fixed dose combinations containing metoprolol have the advantage that beta-blockers are drugs for which there is most evidence that they are cardioprotective; metoprolol is the best documented beta-blocker in this context. The early combination of conventional release metoprolol and hydrochlorothiazide was inadequately investigated by modern standards, but proved well tolerated and effective in clinical practice. The introduction of the long acting metoprolol CR/ZOK (controlled release/zero order kinetics) produced a very satisfactory once daily preparation with no major pharmacokinetic interactions. The fixed dose combination of felodipine and metoprolol CR/ZOK has been well investigated. The two agents complement each other's actions and together provide very effective blood pressure control, cardioprotection and very good tolerability. A case can be made that this preparation more closely meets the requirements of an ideal antihypertensive than a single agent given alone.

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.

Effect of nifedipine tablets on ambulatory blood pressure in patients aged less than 60 and greater than 65 years with systemic hypertension

To evaluate the effect of age on the pattern of circadian blood pressure after nifedipine tablets, ambulatory blood pressure after administration of low and high doses of nifedipine, taken twice daily, was measured over a 24-hour period in 10 elderly and 8 young hypertensive patients. After a 2-week control period without antihypertensive drug, 10 mg of nifedipine was administered twice daily for 2 weeks (low-dose period), followed by 2 weeks of 20 mg (high-dose period). At the end of each period, ambulatory BP monitoring was conducted every 30 minutes for 24 hours, using an ABPM 630 (Nippon-Colin, Komaki, Japan). In both groups, averages of systolic and diastolic BP for the entire day decreased significantly from the control to the low-dose periods. However, after the high-dose period, only the elderly group had further significant reduction of systolic BP, whereas no further reduction was seen in the young group. Separate analysis of whole-day data into daytime and nighttime values revealed that a further decrease in systolic BP after the high-dose period in the elderly group was a reflection of nighttime decline. It was suggested that circadian BP patterns after administration of nifedipine tablets in the elderly differed from those in young hypertensive patients, especially after administration of the high-dose.

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.

Antihypertensive therapy in the aged patient. Clinical pharmacokinetic considerations

The incidence of both systolic and diastolic hypertension is increased in elderly patients, therefore antihypertensive drugs are commonly used in this population. In addition to changes in blood pressure, the aging process also causes numerous changes in other physiological parameters, resulting in altered pharmacokinetic and pharmacodynamic responses to the drugs. The dosage regimens for thiazide diuretics and amiloride must be individually titrated in the elderly patient, since the elimination of these agents decreases concurrently with decreased renal function, as indicated by compromised creatinine clearance. The initial doses of the calcium antagonists should be decreased in elderly patients, since representative compounds from all 3 chemically heterogeneous classes have been shown to have decreased clearance in these patients which appears to be primarily due to the status of hepatic function in the patient. However, with verapamil, the dosage should be further decreased in association with compromised renal function. The dosage of the angiotensin converting enzyme (ACE) inhibitors should be adjusted according to renal function rather than age. Lisinopril, which is primarily eliminated unchanged, is usually given in lower doses in the elderly, and doses of both captopril and enalapril may need to be reduced, depending on renal function. While there is no need to adjust the dosage regimen for the alpha-adrenoceptor blocking drugs (prazosin, terazosin), caution should be used with the beta-adrenergic blockers, particularly the hydrophilic agents, since they are renally eliminated. Labetalol may be a suitable alternative beta-blocker for the elderly patient, since its pharmacodynamic properties of decreased systemic vascular resistance without changes in heart rate or stroke volume are preferential for the elderly patient, and its pharmacokinetics are relatively unchanged in this population. Drugs that act primarily through the central nervous system, such as clonidine, methyldopa and guanfacine, require smaller doses in the presence of renal dysfunction. In contrast, guanabenz is metabolised primarily by the liver, so it would appear to be useful in elderly patients with renal dysfunction despite the lack of studies in this population. Guanadrel, an adrenergic neuron blocking drug, also requires a dosage reduction in patients with impaired renal function. In addition to the pharmacokinetic changes that occur in the elderly patient, pharmacodynamic changes may also be anticipated due to receptor modifications. Older patients have a decrease in beta-receptor sensitivity, while alpha-receptor sensitivity does not change. When designing the dosage regimen for a senior patient with hypertension, the combination of all these variables must be considered.

Hepatic drug metabolism and aging

Although there is considerable variation in the effect of age on drug biotransformation, the metabolism of many drugs is impaired in the elderly. Age-related physiological changes, such as a reduction in liver mass, hepatic metabolising enzyme activity, liver blood flow and alterations in plasma drug binding may account for the decreased elimination of some metabolised drugs in the elderly. It is difficult, however, to separate an effect of aging from a background of marked variation in the rate of metabolism due to factors such as individual metabolic phenotype, environmental influences, concomitant disease states and drug intake. The prevailing data suggest that initial doses of metabolised drugs should be reduced in older patients and then modified according to the clinical response. In most studies the elderly appear as responsive as young individuals to the effects of compounds which induce or inhibit the activity of cytochrome P450 isozymes. Concurrent use of other agents, which induce or inhibit drug metabolism, mandates dose adjustment as in younger patients. Many questions remain unanswered. For instance, limitations of in vitro studies prevent any firm conclusion about changes in hepatic drug metabolising enzyme activity in the elderly. With aging, some pathways of drug metabolism may be selectively affected, but this has not been adequately scrutinised. The possibility that metabolism of stereoisomers may be altered in the elderly has not been adequately tested. The effect of aging on the distribution of polymorphic drug metabolism phenotypes is still not established, despite potential implications for disease susceptibility and survival advantage.

Clinical pharmacokinetic considerations in the elderly. An update

There are numerous studies of drug handling in the elderly, but it is difficult to assess the significance of changes seen in vitro, or after single-dose administration, because they are often compensated by other mechanisms at steady-state. However, a knowledge of these studies is important as the results alert the investigator to possible treatment problems. The high incidence of adverse drug reaction in the elderly population leaves no doubt that improvements in therapy are needed. Research has been directed at seeking patterns of abnormality in the elderly on which to base recommendations for alterations in dosage regimens. The major shortcoming of this approach has been the failure to distinguish between the effect of chronological age on drug pharmacokinetics, and drug kinetics in elderly people with multiple pathology. The latter concern appreciates the variety of factors involved and the importance of treating each patient as an individual: presentation of mean data is confusing and misleading. The objective of drug treatment in any age group, but particularly in the elderly, is to administer the smallest possible dose which gives adequate therapeutic benefit throughout the entire dosage interval with the minimum of side effects. For most drugs the safe starting dose in the elderly is one-third to half that recommended in the young. Vigilance for potential side effects with plasma concentration monitoring, if available, should help keep toxicity to a minimum. When other medications are added or changed, the possibility of interaction should be anticipated. Methods for individualisation of dosage regimens and the use of sustained-release formulations in the elderly are discussed. Dosage alteration in the elderly in terms of reduced dose frequency, rather than dose size, may help improve compliance. A knowledge of the pharmacokinetics of a drug helps determine which approach will be most beneficial.

Metoprolol-controlled release, zero order kinetics

Metoprolol CR/ZOK (controlled release, zero order kinetics) is a new formulation of an extensively used beta 1-selective, beta-adrenoceptor blocking drug, (beta 1-blocker), designed to provide continuous, even, plasma concentrations in the therapeutic range. It should, therefore, provide an effective well-tolerated treatment for hypertension and angina pectoris and for use in secondary prevention following a myocardial infarct. The purpose of this review is to consider the need for such a formulation, to describe its pharmaceutical development, review its pharmacology and assess its efficacy and tolerability compared with other available agents.

Ranitidine versus cimetidine. A comparison of their potential to cause clinically important drug interactions

The literature on H2-antagonist drug interactions is now extensive. The whole subject is so complicated as to make things difficult for the potential prescriber. However, it is possible to reduce most of the information contained in the literature to a few simple messages. Firstly, H2-antagonists bind to cytochrome P450 and may inhibit the metabolism of drugs eliminated by the mixed function oxygenase system. In this respect, cimetidine has a marked effect which, in most studies, has reached statistical significance. Ranitidine, on the other hand, has a much weaker effect which, even if demonstrable, is statistically non-significant. The potential benefit of ranitidine, however, has to be weighed against the relative costs of the 2 drugs. Secondly, H2-antagonists inhibit gastric acid production and may alter the rate of gastric emptying, and hence the rate of drug absorption. They may also have some effect on portal vein and hepatic artery flow. However, these effects are small and probably not clinically relevant. Thirdly, pharmacodynamic effects of H2-antagonist-drug interactions are difficult to demonstrate in planned studies, and although they are reported from time to time, adverse reactions of consequence are relatively uncommon. Fourthly, the prescriber needs to be aware that cimetidine may produce higher plasma concentrations of some drugs which have a fairly narrow therapeutic range, and this may be clinically important. Examples of drugs for which it may be undesirable to inadvertently increase plasma concentrations include warfarin, theophylline and phenytoin. Finally, for most drugs metabolised by the liver, the risk of an important interaction is small. However, if such an interaction is noted it may be helpful to refer to the other reported cases, and a number of references are included here.

Analysis of alpha-hydroxy metabolites of metoprolol in human urine after phosgene/trimethylsilyl derivatization

Three metoprolol metabolites containing an alpha-hydroxy group were identified in human urine by capillary column gas chromatography/mass spectrometry. After aqueous phase cyclization with phosgene the neutral or acidic derivatives formed were isolated by solvent extraction at pH 10 or 3, respectively. Following silylation the electron impact mass spectra of the metabolites exhibited a characteristic ion at m/z 336 of high abundance which originated from cleavage of the bond adjacent to the alpha-OTMS group. Most probably the identified compounds were formed by further biotransformations of alpha-hydroxy metoprolol, which is a primary metabolite. The analytical method is applicable to detect the metoprolol metabolites reported so far. A quantitative assay for one of the metabolites (H 119/72) with nitrogen selective detection is described. The total amount of this metabolite excreted by one subject within 24 h after dosing was about 0.25% of the given dose.

Influence of smoking and gender on the disposition kinetics of metoprolol

The purpose of this study was to examine the influence of cigarette smoking and gender on the pharmacokinetics of metoprolol. Eighteen volunteers with no evidence of clinical disease each randomly received the following doses of metoprolol tartrate: 100 mg orally, 200 mg orally and 20 mg as a constant-rate intravenous infusion over 20 min. The only significant difference between smokers (S) and nonsmokers (NS) was that S had a larger steady-state volume of distribution (3.3 vs 2.5 l/kg). There were no differences in half-life, systemic clearance or bioavailability (f). No differences were observed between males (M) and females (FM) for any of the kinetic parameters examined. Systemic bioavailability varied markedly between subjects (range: 15 to 92%). In fifteen of the eighteen subjects, f was higher after the 200-mg dose compared to the 100-mg dose. These results suggest that metoprolol may be subject to saturable presystemic elimination and extend the previous observations of Johnsson et al. [1] who showed that f increased from 31% to 46% when doses were increased from 20 to 100 mg. However, the difference in f as the dose is increased is unlikely to be clinically significant since the mean difference is smaller than the variation in f among subjects.

Metoprolol. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in hypertension, ischaemic heart disease and related cardiovascular disorders

During the intervening years since metoprolol was first reviewed in the Journal (1977), it has become widely used in the treatment of mild to moderate hypertension and angina pectoris. Although much data have accumulated, its precise mechanisms of action in these diseases remain largely uncertain. Optimum treatment of hypertension and angina pectoris with metoprolol is achieved through dose titration within the therapeutic range. It has been clearly demonstrated that metoprolol is at least as effective as other beta-blockers, diuretics and certain calcium antagonists in the majority of patients. Although a twice daily dosage regimen is normally used, satisfactory control can be maintained in many patients with single daily doses of conventional or, more frequently, slow release formulations. Addition of a diuretic may improve the overall response rate in hypertension. Several controlled trials have studied the effects of metoprolol administered during the acute phase and after myocardial infarction. In early intervention trials a reduction in total mortality was achieved in one moderately large trial of prolonged treatment, but in another, which excluded patients already being treated with beta-blockers or certain calcium antagonists and where treatment was only short term, mortality was significantly reduced only in 'high risk' patients. Overall results with metoprolol have not demonstrated that early intervention treatment in all patients produces clinically important improvement in short term mortality. Thus, the use of metoprolol during the early stages of myocardial infarction is controversial, largely because of the requirement to treat all patients to save a small number at 'high risk'. This blanket coverage approach to treatment may be more justified during the post-infarction follow-up phase since it has been shown that metoprolol slightly, but significantly, reduces the mortality rate for periods of up to 3 years. Metoprolol is generally well tolerated and its beta 1-selectivity may facilitate its administration to certain patients (e.g. asthmatics and diabetics) in whom non-selective beta-blockers are contraindicated. Temporary fatigue, dizziness and headache are among the most frequently reported side effects. After a decade of use, metoprolol is well established as a first choice drug in mild to moderate hypertension and stable angina, and is beneficial in post-infarction patients. Further study is needed in less well established areas of treatment such as cardiac arrhythmias, idiopathic dilated cardiomyopathy and hypertensive cardiomegaly.

Comparison of pharmacokinetic profiles of single and multiple doses of a slow release Oros oxprenolol delivery system in young normotensive and elderly hypertensive subjects

Oxprenolol in an Oros 8/130 sustained release osmotic pump system (equivalent to 120 mg oxprenolol hydrochloride in a conventional formulation and releasing 8 mg h-1) was given to eight normal young subjects (mean age 23 years) and eight elderly hypertensive patients (mean age 77 years). The plasma concentration-time profiles of oxprenolol were determined over 32 h using gas liquid chromatography after the initial dose and following seven doses. The elderly patients had a significantly higher AUC and maximum plasma oxprenolol concentration following both the first and final doses studied. It is unlikely that this difference is due to a prolonged absorption phase in the elderly patients. Reduced drug clearance seems the most probable explanation.

Age-related changes in drug handling in man

Persons older than 65 years constitute 10% of the U.S. population but require approximately one-third of its health care service. A significant proportion of their disease states is related to adverse reactions to prescribed drugs. The origins of this disturbingly high incidence of untoward consequences from drug therapy are multiple and complex. They include: (1) alterations in expected patterns of drug handling associated with physiologic changes of the aging process itself, (2) alterations in responsiveness to specific types of drugs and (3) frequent occurrence of chronic and acute diseases. The data documenting pharmacokinetic changes in aging subjects are rudimentary, and the physician is commonly aware only of pharmacokinetic profiles derived from studies in healthy, young subjects. Without a firm basis on which to rest pharmacologic therapy, the clinical approach to drug treatment in the elderly patient must be cautious and conservative.

Beta-blocking effect and pharmacokinetics of pindolol in young and elderly hypertensive patients

The pharmacokinetics and beta-blocking effect of pindolol has been compared in 20 patients with essential hypertension (WHO Stage I), 10 below 25 years of age and 10 older than 60 years. Each patient received pindolol 10 mg p.o. once a day for 5 days. The area under the curve (AUC) of pindolol was larger in the old than in the young patients both on the first (p less than 0.05) and the fifth (p less than 0.01) days. The AUC of pindolol was 14% higher on the fifth day compared to the first day in the elderly group, indicating minor accumulation at steady-state. There was no change in AUC in the young patients. Endogenous creatinine clearance was lower in the old (80 +/- 9 ml/min) than in the young patients (150 +/- 45 ml/min). The beta-blocking effect did not differ between the groups at 2 h after administration of pindolol on Days 1 or 5. However, 24 h after the first and fifth doses approximately 60% of the beta-blockade persisted in the old group whereas 17 and 19% of the beta-blockade, respectively, persisted in the young group; the difference between the groups was statistically significant (p less than 0.01). The most probable explanation for the more sustained beta-blocking effect in the elderly is the physiologically decrease in renal function, which results in a more sustained plasma level of pindolol in those patients.

A comparison of the pharmacokinetics of atenolol, metoprolol, oxprenolol and propranolol in elderly hypertensive and young healthy subjects

Six elderly patients with established hypertension and six young healthy subjects were studied after 8 days of treatment with atenolol 50 mg day-1, metoprolol 50 mg day-1, oxprenolol 80 mg day-1 and propranolol 80 mg day-1. The area under the blood concentration-time curve was increased in the elderly group for each drug, but the difference was statistically significant only for atenolol. The lower serum albumin concentrations in the elderly group did not result in a decrease in the percentage of propranolol or oxprenolol bound to serum proteins.

Pharmacokinetics of pirprofen in young volunteers and elderly patients

Plasma concentrations of pirprofen were measured in 11 elderly arthritic patients and 6 healthy young volunteers at the beginning and end of 8 days treatment with 400 mg doses twice daily. The mean ages of the two groups were 74.5 and 21.8 years, respectively. There were no statistically significant differences in peak concentrations, times to peak, areas under the curve or terminal elimination half-lives between the groups after single dosing. Repeated dosing increased plasma drug concentrations in both groups but the extent was as predicted from the single dose data. Again there were no statistically significant differences between the groups, although pre-dosing plasma concentrations were higher in the elderly compared with the young individuals. The results of this relatively small study suggest that advancing age and arthritic disease appear to have little influence on the pharmacokinetics of pirprofen and no modification in the dosage recommendation in elderly patients without overt renal or hepatic impairment is indicated.

Influence of food on the absorption of metoprolol administered as an Oros drug delivery system to man

The influence of food on the release, absorption and metabolism of metoprolol has been studied after single administration of a 19/190 Oros system to eight healthy volunteers on four occasions, once after an overnight fast, and just before each of three daily meals (breakfast, lunch and dinner). The plasma concentration-time profiles under the four test conditions were virtually identical, and no statistically significant differences in mean areas under the curves between 0 and 32 h, peak concentrations, or times to peak, were detected. The absorption of metoprolol was unaffected by food intake, with 80-90% of the amount absorbed reaching the systemic circulation within 10 h. The ratios of areas under the curve for alpha-hydroxymetoprolol to its parent drug were in the same range for the four treatments, and similar to those reported after conventional tablets. The in vivo release and absorption of drug from the Oros system and its systemic availability, were not influenced by concomitant ingestion of food.

Investigation of drug absorption from the gastrointestinal tract of man. III. Metoprolol in the colon

The colonic absorption of metoprolol was indirectly evaluated by measuring drug appearance in plasma following intravenous, jejunal or colonic infusion in six healthy volunteers. Plasma concentrations of alpha-hydroxymetoprolol and urinary excretion of the main metabolites were also measured. Plasma profiles of metoprolol after colonic and jejunal perfusion were similar, and the relative bioavailabilities of the drug from these two regions of the gut were not significantly different. The concentrations of alpha-hydroxymetoprolol, the major metabolite in plasma, were similar after jejunal and colonic perfusion, but higher than those observed after intravenous administration. The percentage of the dose recovered in urine over 24 h as two metabolites was not significantly influenced by the route of administration.

Simultaneous determination of metoprolol and metabolites in urine by capillary column gas chromatography as oxazolidineone and trimethylsilyl derivatives

A method for the determination of metoprolol and its main metabolites in urine is presented. The method comprises derivatization of the aminopropanol side-chain with phosgene at alkaline pH and isolation in an organic phase at acidic pH. After trimethylsilylation, separation and quantification are performed by capillary column gas chromatography with flame ionization detection. The reaction is performed at pH 12 with 60 microliters of 2 M phosgene in toluene added in three portions. Diethyl ether--dichloromethane is used as extraction medium and bis(trimethylsilyl) acetamide as silylating agent. With spiked samples linear standard curves were obtained for metoprolol and three of its main metabolites with a detection limit varying between 4 and 20 mumol/l of urine. The method was applied to urine samples from a normal individual who had taken 292 mumol of metoprolol as tartrate.

Pharmacokinetics of metoprolol in healthy, elderly, non-smoking individuals after a single dose and two weeks of treatment

The effect of long-term treatment on the absorption and disposition of metoprolol has been evaluated in 8 healthy, non-smoking, elderly individuals (mean age 74.5 years) and in a control group of 8 healthy, young individuals. Two trace doses of [3H]metoprolol were given i.v., first concomitantly with a single oral 50 mg dose of cold metoprolol, and second, with the morning dose after 2 weeks of treatment with 50 mg b.d. In the elderly, the mean AUC increased by about 45% (p less than 0.05) over the treatment period, while in the control group the mean AUC was 18% greater (p less than 0.05) on Day 14 than on Day 1. In the elderly, changes both in pre-systemic elimination and in total body clearance accounted for the elevation of the AUC, whereas reduced first-pass effect appeared to be the major cause of the increased steady-state plasma level in the control group. With the exception of the volume term, V beta, the pharmacokinetic parameters were not significantly different between the elderly and the young individuals. For this reason, almost identical steady-state plasma levels were attained in the two groups. The results suggest that age-related physiological changes may have some minor effects on the pharmacokinetics of metoprolol, and also that the changes do not lead to significantly altered plasma concentrations compared to those in young individuals.