Comparison of the pharmacodynamic and pharmacokinetic profiles of single and multiple doses of a commercial slow-release metoprolol formulation with a new Oros delivery system

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.

The relevance of CYP2D6 genetic polymorphism on chronic metoprolol therapy in cardiovascular patients

BACKGROUND AND OBJECTIVE

CYP2D6 polymorphisms are well described in normal populations but there are few data on its clinical significance. We therefore investigated the influence of CYP2D6 polymorphism on steady-state plasma concentrations and apparent oral clearance of metoprolol in patients with cardiovascular diseases.

METHODS

Ninety-one patients on metoprolol were recruited. Plasma concentrations of metoprolol and alpha-hydroxy metoprolol were measured at 4-h post-dose. CYP2D6 genotyping (*1, *3, *4, *5, *9, *8, *10, *17 and duplication) were performed on the DNA extracted. Ratio of plasma concentrations of metoprolol and alpha-hydroxy metoprolol and the apparent oral clearance of metoprolol were calculated. The influences of CYP2D6 genotypes were investigated.

RESULTS

A 100-fold variation was noted for both plasma concentrations of metoprolol and alpha-hydroxy metoprolol. There was a weak correlation between the total daily doses and plasma concentrations of both. Plasma concentrations were found to be higher in patients with genotypes that predicted lower enzyme activity. One patient homozygous for CYP2D6*4 had the highest metoprolol concentration per unit dose. With an antimode of 10. Two patients were identified as poor metabolizers (PMs) (2.1%; 95% CI: 2.9). The PMs who had a plasma metabolic ratio (pMR) of 37.8 was homozygous CYP2D6*4 whereas the other with pMR 14.5 was genotyped CYP2D6 *4/*10. There was a 36-fold difference between the highest and lowest clearance values. Large overlaps in the clearance values were noted between most of the genotypes.

CONCLUSIONS

Our data suggest that pharmacogenetic measures could be used to design a more individualized metoprolol dosage regimen for patients.

Osmotically controlled oral drug delivery

It is advantageous to deliver some drugs with short half-life, and which are to be given frequently for chronic ailments, in the form of controlled-release (CR) formulations. The orally administered drugs, in the form of conventional matrix or reservoir type formulations, pose problems of bioavailability fluctuations due to gastric pH variations. Moreover, the release of drug(s) from these systems is affected by the hydrodynamic conditions of the body. Osmotically controlled drug delivery systems utilize the principles of osmotic pressure for the controlled delivery of active agent(s). The release rate of drug(s) from these systems is independent of the physiological factors of the gastrointestinal (GI) tract to a large extent. In the present review, theory underlying the delivery of drugs from osmotic systems is presented. Different types of oral osmotic systems, their advantages over conventional matrix and reservoir types of systems, and their applications are also discussed. Finally, some of the limitations, adverse effects, and patent and market status of these systems are reviewed. These systems form a major segment of drug delivery products. Because of their advantages and strong market potential, it appears that the future of osmotic systems in rate-controlled oral drug delivery is promising.

Design and evaluation of an osmotic pump tablet (OPT) for chlorpromazine using (SBE)7m-beta-CD

PURPOSE

The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) which exhibits pH-independent release profiles for a basic drug using a sulfobutyl ether-beta-cyclodextrin, (SBE)7m-beta-CD, which acts as both a solubilizer and as an osmotic agent.

METHODS

Chlorpromazine free base (CLP) was chosen as a model drug for this study. The release of CLP from osmotic pump tablets was studied in vitro. In vivo absorption of CLP from the OPT was evaluated in male beagle dogs.

RESULTS

The CLP release profile from an OPT prepared from a core tablet composed of a 1:10 molar ratio of CLP to (SBE)7m-beta-CD was pH-independent, and was controlled by modulating the membrane thickness of the OPT. Another cyclodextrin, hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and a sugar mixture of lactose and fructose resulted in pH-dependent release at the same molar ratio. An in vivo absorption study in dogs with an OPT containing (SBE)7m-beta-CD correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method.

CONCLUSIONS

In addition to serving as a solubilizer and osmotic agent, (SBE)7m-beta-CD can also serve as the controlling agent for pH independent release of CLP from OPTs. This system successfully modified the in vivo input rate of CLP without compromising oral bioavailability.

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.

Pulmonary effects of long-term beta 2-blockade in healthy subjects: comparative study of metoprolol OROS

The effects on airway response of metoprolol OROS (oral osmotic) and three other long-acting beta-adrenoceptor blockers were studied. This was a placebo-controlled, randomized, five-period, single-blind, crossover trial in 15 healthy volunteers. Bronchial beta-blockade was estimated as the displacement of the salbutamol bronchodilator response of specific airway conductance (SGAW) measured by whole-body plethysmography. Metoprolol OROS (14/190 mg), slow-release (SR) metoprolol (200 mg), atenolol (100 mg), long-acting (LA) propranolol (160 mg), and placebo were given once daily for 7 days. Inhaled salbutamol was administered at peak drug levels in cumulative doses of 12.5 to 800 micrograms on day 5 and in a single dose of 400 micrograms on day 7. On day 5, salbutamol induced significant increases in SGAW in each treatment group. SGAW increased after the single dose of salbutamol on day 7 in all groups and then declined steadily. The highest values were found after placebo and metoprolol OROS, with smaller increases after SR metoprolol, atenolol, and LA propranolol, the latter showing the smallest increase. Therefore, it would appear that under steady-state conditions, beta 2-bronchial receptors are least blocked by metoprolol OROS, followed by SR metoprolol, atenolol, and LA propranolol.

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.

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

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

Plasma concentration-response relationships of two formulations of propranolol

The time-course of beta blockade induced by two formulations of propranolol was compared to their plasma concentration-time curves. Graded infusions of isoproterenol were used to assess the degree of beta blockade at different times after oral administration of 80 mg of propranolol to 11 healthy volunteers. The time-course of drug effect was measured as the decline of the systolic pressor dose 20 (SPD 20) and the chronotropic dose 20 (CD 20). Variability of plasma propranolol concentration was small, varying within subjects from 27% to 36% and between subjects from 19% to 28% at the various sampling times. Pharmacodynamic effects showed a similar reproducibility: intra-individual variation was 15% to 28% for CD 20 and 17% to 32% for SPD 20; interindividual variation was 10% to 24% for CD 20 and 13% to 23% for SPD 20. Pooling of the data of all subjects indicated a parallel decline of drug concentration and effect. However, three of the 11 subjects showed drug effects declining at a faster rate than drug levels. This dissociation between serum concentrations and effects points out the clinical relevance of complementing kinetic studies of propranolol with pharmacodynamic studies. The good reproducibility within subjects and the small interindividual variation suggests that isoproterenol dose-response curves may be a useful tool for such studies.

A multiple dose pharmacokinetic and pharmacodynamic evaluation of conventional and 19/285 Oros formulations of metoprolol in healthy volunteers

Plasma metoprolol concentrations and haemodynamic effects have been measured in six healthy male volunteers during once daily dosing with a 19/285 Oros system and twice daily dosing with 100 mg conventional tablets, on two separate occasions. Plasma drug concentrations throughout the day varied less with the Oros than with the conventional tablet regimen. Predosing concentrations were also higher with Oros but areas under the curve, after correcting for the differences in dose, were similar for the two preparations. Inhibition of exercise tachycardia was drug concentration dependent and was smoothly controlled through the day only with the Oros preparation. Predosing effects at steady-state were also greater for the Oros regimen. The decline in mean blood pressure, however, showed the same daily pattern for both regimens, and no significant differences were detected between Oros and conventional tablet treatments. The smoothness of the plasma profiles after Oros confirmed the controlled-release performance of the system in vivo and indicates its potential in the treatment of angina, cardiac arrhythmias and wherever it is important not to jeopardize steady selective beta-adrenoceptor blockade.

Osmotically controlled-delivery of metoprolol in man: in vivo performance of Oros systems with different durations of drug release

In vivo absorption from 19/190 and 19/285 metoprolol Oros drug delivery systems has been assessed by measuring plasma drug concentrations after single administration of the systems to six healthy volunteers. The initial in vitro release rate for both Oros preparations was 19 mg/h but they contained 190 or 285 mg of metoprolol fumarate. The plasma concentration-time profiles for both Oros dosage forms were consistent with an extended duration of release and absorption from the gastrointestinal tract. Analysis of the plasma level data indicated that the rate and duration of in vivo absorption closely mirrored the in vitro release behaviour of the 19/190 and 19/285 systems, but the in vivo profiles showed a 1-2 h initial delay. The administration of the 19/190 system on two occasions to the same six volunteers indicated that in vivo release of drug from this Oros preparation was reproducible.

Comparison of single-dose pharmacokinetic and pharmacodynamic properties of two metoprolol Oros systems with different initial zero-order release rates

Plasma concentrations and haemodynamic effects at rest and during exercise have been measured in six healthy volunteers after single oral dosing with two Oros drug delivery systems containing 190 mg metoprolol fumarate but with initial release rates of 14 and 19 mg/h, respectively. Sub-maximal exercise heart rates were attenuated by both Oros systems throughout most of the 30 h study period but no significant differences were detected between the 14/190 and 19/190 forms. Resting pulse rates and blood pressure were similarly affected by the Oros preparations. Approximately the same amount of drug reached the circulation from the Oros systems, but the 19/190 form produced higher peak concentrations at earlier times after dosing. At 24 h higher plasma concentrations were observed for the 14/190 preparation, reflecting its longer duration of drug release. There was no apparent advantage of one form over the other as regards haemodynamic response. The reduced peak plasma concentration with 14/190 Oros may, however, be an advantage in terms of tolerability.

Polymorphic metabolism of beta-adrenoceptor antagonists

Most beta-adrenoceptor blockers undergo extensive oxidative metabolism. The evidence for polymorphism of the debrisoquine type is reviewed. The AUC and half-life of metoprolol were considerably greater in poor metabolisers (PM) of debrisoquine than in extensive metabolisers (EM). Metoprolol alpha-hydroxylation is impaired and O-dealkylation must also be affected. Polymorphism in the former route has been demonstrated in a population of 143 patients to be directly related to debrisoquine phenotype. Bufuralol AUC and half-life are much higher in PM than EM subjects. Hydroxylation at the 1 and 4 positions are affected. Genetic polymorphism for 1-hydroxylation has been shown in family and population studies. Propranolol 4-hydroxylation is defective in PM subjects of debrisoquine but propranolol AUC is not related to phenotype, presumably because other major pathways are unaffected. Oxidation phenotype correlates well with intensity and duration of beta-adrenoceptor blockade after metoprolol, PM subjects requiring only once-daily dosing. However, in EM subjects twice-daily dosing is required even if slow release preparations are used, since plasma metoprolol concentrations may remain negligible 24 h after dosing. The beta-adrenoceptor blocking effects of propranolol and bufuralol are unlikely to be influenced by oxidation status. Anecdotal reports of toxicity arising in PM subjects taking metoprolol or propranolol need to be substantiated. However, vomiting after the administration of bufuralol often occurs in poor metabolisers. Metabolic interactions with drugs sharing the same enzyme system are discussed. Debrisoquine and bufuralol competitively inhibit each other's metabolism in vitro. (ABSTRACT TRUNCATED AT 250 WORDS)