The effect of antacid, metoclopramide, and propantheline on the bioavailability of metoprolol and atenolol

The Use of Physiologically Based Pharmacokinetic Analyses-in Biopharmaceutics Applications -Regulatory and Industry Perspectives

The use of physiologically based pharmacokinetic (PBPK) modeling to support the drug product quality attributes, also known as physiologically based biopharmaceutics modeling (PBBM) is an evolving field and the interest in using PBBM is increasing. The US-FDA has emphasized on the use of patient centric quality standards and clinically relevant drug product specifications over the years. Establishing an in vitro in vivo link is an important step towards achieving the goal of patient centric quality standard. Such a link can aid in constructing a bioequivalence safe space and establishing clinically relevant drug product specifications. PBBM is an important tool to construct a safe space which can be used during the drug product development and lifecycle management. There are several advantages of using the PBBM approach, though there are also a few challenges, both with in vitro methods and in vivo understanding of drug absorption and disposition, that preclude using this approach and therefore further improvements are needed. In this review we have provided an overview of experience gained so far and the current perspective from regulatory and industry point of view. Collaboration between scientists from regulatory, industry and academic fields can further help to advance this field and deliver on promises that PBBM can offer towards establishing patient centric quality standards.

Exercise Is Medicine, But Does It Interfere With Medicine?

Exercise frequently is prescribed therapeutically, either on its own or combined with drugs. A drug's absorption, distribution, metabolism, and excretion can be affected by the user's anatomy and physiology, which are both changed by the myriad of complex adaptations to acute and chronic exercise. This article reviews the research that suggests exercise may influence a drug's plasma concentration, and thus its efficacy and safety.

Clinically significant drug interactions with antacids: an update

One may consider that drug-drug interactions (DDIs) associated with antacids is an obsolete topic because they are prescribed less frequently by medical professionals due to the advent of drugs that more effectively suppress gastric acidity (i.e. histamine H(2)-receptor antagonists [H2RAs] and proton pump inhibitors [PPIs]). Nevertheless, the use of antacids by ambulant patients may be ever increasing, because they are freely available as over-the-counter (OTC) drugs. Antacids consisting of weak basic substances coupled with polyvalent cations may alter the rate and/or the extent of absorption of concomitantly administered drugs via different mechanisms. Polyvalent cations in antacid formulations may form insoluble chelate complexes with drugs and substantially reduce their bioavailability. Clinical studies demonstrated that two classes of antibacterials (tetracyclines and fluoroquinolones) are susceptible to clinically relevant DDIs with antacids through this mechanism. Countermeasures against this type of DDI include spacing out the dosing interval - taking antacid either 4 hours before or 2 hours after administration of these antibacterials. Bisphosphonates may be susceptible to DDIs with antacids by the same mechanism, as described in the prescription information of most bisphosphonates, but no quantitative data about the DDIs are available. For drugs with solubility critically dependent on pH, neutralization of gastric fluid by antacids may alter the dissolution of these drugs and the rate and/or extent of their absorption. However, the magnitude of DDIs elicited by antacids through this mechanism is less than that produced by H2RAs or PPIs; therefore, the clinical relevance of such DDIs is often obscure. Magnesium ions contained in some antacid formulas may increase gastric emptying, thereby accelerating the rate of absorption of some drugs. However, the clinical relevance of this is unclear in most cases because the difference in plasma drug concentration observed after dosing shortly disappears. Recent reports have indicated that some of the molecular-targeting agents such as the tyrosine kinase inhibitors dasatinib and imatinib, and the thrombopoietin receptor agonist eltrombopag may be susceptible to DDIs with antacids. Finally, the recent trend of developing OTC drugs as combination formulations of an antacid and an H2RA is a concern because these drugs will increase the risk of DDIs by dual mechanisms, i.e. a gastric pH-dependent mechanism by H2RAs and a cation-mediated chelation mechanism by antacids.

Pharmacokinetics and interactions of headache medications, part II: prophylactic treatments

The present part II review highlights pharmacokinetic drug-drug interactions (excluding those of minor severity) of medications used in prophylactic treatment of the main primary headaches (migraine, tension-type and cluster headache). The principles of pharmacokinetics and metabolism, and the interactions of medications for acute treatment are examined in part I. The overall goal of this series of two reviews is to increase the awareness of physicians, primary care providers and specialists regarding pharmacokinetic drug-drug interactions (DDIs) of headache medications. The aim of prophylactic treatment is to reduce the frequency of headache attacks using beta-blockers, calcium-channel blockers, antidepressants, antiepileptics, lithium, serotonin antagonists, corticosteroids and muscle relaxants, which must be taken daily for long periods. During treatment the patient often continues to take symptomatic drugs for the attack, and may need other medications for associated or new-onset illnesses. DDIs can, therefore, occur. As a whole, DDIs of clinical relevance concerning prophylactic drugs are a limited number. Their effects can be prevented by starting the treatment with low dosages, which should be gradually increased depending on response and side effects, while frequently monitoring the patient and plasma levels of other possible coadministered drugs with a narrow therapeutic range. Most headache medications are substrates of CYP2D6 (e.g., beta-blockers, antidepressants) or CYP3A4 (e.g., calcium-channel blockers, selective serotonin re-uptake inhibitors, corticosteroids). The inducers and, especially, the inhibitors of these isoenzymes should be carefully coadministered.

Sevelamer hydrochloride (Renagel), a phosphate-binding polymer, does not alter the pharmacokinetics of two commonly used antihypertensives in healthy volunteers

Sevelamer hydrochloride (Renagel) is a nonabsorbed phosphate-binding polymer approved for the treatment of hyperphosphatemia in adult hemodialysis patients. The authors studied the potential effect of sevelamer on the pharmacokinetics of two antihypertensive drugs, enalapril (20 mg) and metoprolol (100 mg), commonly used in end-stage renal disease patients. Two studies were conducted. Both were single dose, crossover design with or without a 2.4 g dose of sevelamer in healthy volunteers. Within each study, there was a 7-day washout interval between the two dose administrations. There were 28 volunteers in the enalapril study and 32 in the metoprolol study. The mean plasma concentrations versus time profiles of enalapril, enalaprilat, and metoprolol were not altered by the simultaneous administration of sevelamer. Values for the ratio of ln[AUC(0-infinity)], ln[AUC(0-t)], and ln(Cmax] with and without sevelamer were approximately 100%, and the 90% confidence intervals for the ratios of these parameters with and without sevelamer were within the 80% to 125% range in all cases except for the ln[Cmax] of enalapril, which had an upper confidence bound of 125.4%. The authors conclude that sevelamer does not interfere with the absorption and elimination of enalapril and metoprolol.

Comparative pharmacokinetic study of a floating multiple-unit capsule, a high-density multiple-unit capsule and an immediate-release tablet containing 25 mg atenolol

The purpose of this study was to evaluate the possible advantages of floating and high-density dosage forms and their influence on pharmacokinetic parameters. Atenolol was chosen as a model drug because of its poor absorption in the lower gastrointestinal tract. Three formulations containing 25 mg atenolol, a floating multiple-unit capsule, a high-density multiple-unit capsule, and an immediate-release tablet were compared with respect to estimated pharmacokinetic parameters. The two multiple-unit dosage forms were composed of compressed minitablets and had sustained release properties. The bioavailability of the two gastroretentive preparations with sustained release characteristics was significantly decreased when compared to the immediate-release tablet. The floating minitablets seemed to be retained longer in the stomach than the high-density dosage form. The first atenolol concentration detectable in the plasma and the time to peak Tmax were delayed for the floating dosage form. For the parameters Cmax and AUC 0-infinity, the lower limit of the 90% confidence interval was outside the bioequivalence range (0.80-1.25). This study showed that it was not possible to increase the bioavailability of a poorly absorbed drug such as atenolol using gastroretentive formulations. Atenolol absorption was delayed and the maximum plasma concentration was diminished.

Pharmacological attempts to improve the bioavailability of oral etoposide

Etoposide demonstrates incomplete and variable bioavailability after oral dosing, which may be due to its concentration and pH-dependent stability in artificial gastric and intestinal fluids. The use of agents that may influence etoposide stability and, thereby, bioavailability, was investigated in a number of clinical studies. Drugs that influence the rate of gastric emptying, while modulating the time of drug absorption, did not significantly alter the etoposide area under the concentration-time curve (AUC) or bioavailability. Specifically, metoclopramide had little effect on the etoposide absorption profile and did not significantly alter the AUC (AUC with etoposide alone, 68.4 +/- 20.3 micrograms ml-1 h, versus 74.3 +/- 25.9 micrograms ml-1 h with metoclopramide), suggesting that in most patients the drug is already emptied rapidly from the stomach. In contrast, propantheline produced a dramatic effect on etoposide absorption, delaying the time of maximal concentration tmax from 1.1 to 3.5 h (P < 0.01), but again without a significant improvement in drug AUC or bioavailability across the 24-h study period (AUC with etoposide alone 78.3 +/- 19.1 micrograms ml-1 h, versus 88.1 +/- 23.6 micrograms ml-1 h with propantheline). The effect of these drugs on the absorption of oral paracetamol, a drug included in the study as a marker of gastric emptying, was exactly the same as that found for etoposide, with no change in AUC being observed after metoclopramide or propantheline administration but a significant delay in tmax being seen on co-administration with etoposide and propantheline. The co-administration of ethanol or bile salts (agents that significantly improved the stability of etoposide in artificial intestinal fluid) with oral etoposide similarly had no effect on improving the etoposide AUC or reducing the variability in AUC, suggesting that drug stability in vivo was not affected by these agents. In the third study the co-administration of cimetidine had no effect on the pharmacokinetics of oral or i.v. etoposide, despite the previous observation that etoposide stability was markedly improved at pH 3-5 as compared with pH 1 in artificial gastric fluid. This series of studies, designed to investigate factors that improved etoposide stability in laboratory studies, failed to demonstrate any potentially useful improvement in AUC or bioavailability in the clinical setting.

Pharmacokinetic drug interactions with gastrointestinal motility modifying agents

Drugs may affect gastrointestinal motility and, therefore, absorption of other concomitantly administered drugs. Gastrointestinal prokinetic agents increase the rate of gastric emptying and also upper intestinal motility. These effects would be expected to increase the initial rate of absorption of orally administered drugs, but reduce total bioavailability of the agents. Metoclopramide has been shown to increase the rate of absorption of several classes of drug, reflected by reduced time taken to achieve maximal plasma concentration (tmax) and increased maximal plasma concentration (Cmax). However, the effect of these agents on the area under the plasma concentration-time curve from zero to infinity (AUC0-infinity), when measured, is not consistent. Cisapride and domperidone appear to have similar effects, but there are relatively less data available regarding these products. Opioids may delay gastric emptying considerably, an effect which will often have significant clinical and therapeutic implications. Most of the data confirming this observation concern oral analgesics, but the effect should be considered when prescribing any oral medication. Drugs with anticholinergic or sympathomimetic activity are likely to have a similar effect and this is confirmed, in the main, by the limited data available. Although many effects reported in the literature are of limited clinical importance, they may be significant when prescribing a drug with a narrow therapeutic index, especially if it is absorbed poorly.

The influence of gastrointestinal transit on drug absorption in healthy volunteers

1. The effect of variability of gastric emptying and oro-caecal transit on the absorption of a multicomponent solution of frusemide, atenolol, hydrochlorthiazide and salicylic acid has been studied in six healthy subjects. Each subject was studied on five separate occasions: three times under basal conditions, once following metoclopramide and once following codeine pretreatment in an attempt to speed and slow transit respectively. 2. Inter-subject variability of gastric emptying, oro-caecal transit and the rate and extent of drug absorption was considerable. 3. The absorption of salicylic acid appeared rate-limited by gastric emptying but the rate and extent of frusemide, atenolol and hydrochlorthiazide absorption were unrelated to measures of gastric emptying or oro-caecal transit. 4. Codeine phosphate caused a two-fold delay in oro-caecal transit but did not influence gastric emptying while metoclopramide had no significant effect on either function. 5. Metoclopramide and codeine had no significant effect on the rate or extent of absorption of any of the study drugs. 6. Within the limits of this experiment, oro-caecal transit time did not appear to be an important determinant of frusemide, atenolol, hydrochlorothiazide or salicylic acid absorption. Other factors must account for the observed variability in drug absorption.

Effects of antacids on the clinical pharmacokinetics of drugs. An update

Since a previous review by Hurwitz was published in 1977 a large number of reports on drug interactions with antacids have appeared, few of which are of clinical relevance. Tetracyclines form insoluble complex molecules by metal ion chelation with various antacids; tetracycline absorption may be decreased by more than 90% by this interaction. Of the new class of quinolone antibiotics, the absorption of ciprofloxacin and ofloxacin is reduced by 50 to 90% in the presence of aluminium- and magnesium hydroxide-containing antacids. In contrast to early work showing inhibition of the absorption of beta-adrenergic blocking drugs by antacids, subsequent studies did not confirm a reduction in the bioavailability of either atenolol or propranolol during antacid treatment; indeed, they showed an increase in the plasma concentrations of metoprolol when the drug was coadministered with an antacid. The bioavailability of captopril was significantly reduced in the presence of an antacid, and lower plasma concentrations of this angiotensin-converting enzyme inhibitor were accompanied by a reduction of its effect on the systolic blood pressure of the patients. The absorption of the cardiac glycosides digoxin and digitoxin is not inhibited by antacids to a significant degree, although earlier studies had shown a positive effect when the dissolution of the glycoside preparations was relatively poor. Antacids reduce the bioavailability of the H2-receptor antagonists cimetidine and ranitidine only when high antacid doses are used and when the drugs are administered simultaneously. The bioavailability of famotidine was not significantly altered by a potent antacid preparation, although a trend towards reduced absorption was observed. Iron absorption is significantly decreased in the presence of sodium bicarbonate and calcium carbonate, but is nearly complete when coadministered with aluminium-magnesium hydroxide. Nonsteroidal anti-inflammatory drugs such as naproxen, tenoxicam, ketoprofen, ibuprofen and piroxicam are not affected in their absorption by antacid treatment. Theophylline bioavailability is unchanged when the drug is given together with antacids, although its rate of absorption may be altered, leading to a reduction or an increase in the time of the occurrence of peak plasma drug concentrations.

Perturbation of upper gastrointestinal transit and antroduodenal motility by experimentally applied stress: the role of beta-adrenoreceptor mediated pathways

A series of three experiments were performed on healthy adult volunteers to investigate the possible role played by beta-adrenoreceptor mediated pathways in the disturbance of human upper intestinal motor function by hand immersion in cold water. In the first experiment, (an extended pilot study on one individual), orocaecal transit of a standard meal was measured on 36 occasions with and without cold water stimulation and with and without a series of alpha and beta blocking drugs. Cold water stimulation consistently delayed transit in this individual, an effect which was attenuated by prior beta-blockade. In a double blind trial of the effect of beta-blocker atenolol v placebo on transit in nine individuals, a consistent reduction in the cold water induced transit delay was observed (p less than 0.01) independent of any direct effect of beta-blockade. In the third experiment seven individuals underwent repeated studies of antroduodenal pressure activity comparing the effects of cold and warm water stimulation with and without beta blockade to determine whether the observed transit effect could be related to an action on gastrointestinal motility. Cold water stimulation reduced antroduodenal motility, but no consistent effects of previous beta blockade were noted. These studies indicate the presence of a beta-adrenoreceptor mediated pathway in the cold water induced delay of orocaecal transit but not in the inhibition of gastroduodenal motility. Further studies are indicated to determine the site and mode of action of this transit effect more precisely.

Effect of cisapride and metoclopramide on digoxin bioavailability

Pharmacokinetics of digoxin were investigated in six healthy volunteers following one week of digoxin monotherapy 0.25 mg b.i.d., and during coadministration of metoclopramide 10 mg t.i.d. or cisapride 10 mg t.i.d.. Metoclopramide reduced the peak plasma concentration of digoxin from 1.5 +/- 0.2 ng/ml to 1.1 +/- 0.1 ng/ml (mean +/- SEM) (p = 0.05), cisapride lowered the peak concentration to 1.3 +/- 0.1 ng/ml (p = 0.14). Metoclopramide prolonged the time required to reach the peak concentration of digoxin from 2 hr to 2.7 hr (p = 0.17), cisapride did not. Digoxin AUC0-12 (743 +/- 79 ng/ml.min) was reduced by 12% on coadministration of cisapride (653 +/- 38 ng/ml.min, p = 0.22) and by 19% on coadministration of metoclopramide (605 +/- 34 ng/ml.min, p = 0.06). It is concluded that the gastrointestinal absorption of digoxin is reduced by both substances. Monitoring of the patient's clinical status should be recommended when metoclopramide and cisapride are coadministered.

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.

Bioavailability studies with ciglitazone in beagles. II. Effect of propantheline bromide and metoclopramide HCL on bioavailability of a tablet

Bioavailability studies in fasted dogs with ciglitazone (CGZ), an oral hypoglycemic agent, suggested that an absorption window could contribute to the poor oral availability of CGZ. If so, propantheline bromide (PPB) could increase the residence time of CGZ at absorption sites and increase its bioavailability. Using this rationale, a Latin square study was conducted with CGZ in fasted dogs (n = 10) using treatments of a single 125 mg tablet with and without 1.2 mg kg-1 i.m. PPB. PPB was given in a single dose 1 h prior to administration of CGZ. Plasma concentrations of CGZ were assayed by HPLC. PPB significantly increased the AUC of CGZ by a ratio of 1.2:1 (p less than 0.01). PPB also increased Tmax from 2-8 h (p less than 0.001), and appeared to produce first order absorption of CGZ. In a separate CGZ study using fasted dogs (n = 10), a single 125 mg tablet was administered with and without i.v. metoclopramide HC1 (MCP). A 10 mg dose of MCP was given 15 min prior to dosing with CGZ and repeated 1 h after dosing. MCP increases GI motility and was expected to decrease residence time of CGZ. MCP had no effect on Tmax, but significantly decreased AUC by 8 per cent (p = 0.05). MCP also reduced Cmax by 16 per cent (p = 0.06). Taken as a whole, these data suggest that the effect of meals to increase bioavailability of CGZ could be mediated at least in part, through an increase in GI residence time.

Metoclopramide. An updated review of its pharmacological properties and clinical use

Since previously reviewed in the Journal (Vol. 12, No. 2), metoclopramide has been confirmed as an effective drug in treating and preventing various types of vomiting and as a useful agent in oesophageal reflux disease, gastroparesis, dyspepsia, and in a variety of functional gastrointestinal disorders. Of considerable importance is the recent evidence of its efficacy when administered intravenously in high dosages in preventing severe vomiting associated with cisplatin. Good results have been achieved in patients not previously treated with cisplatin, but further studies are needed to determine its level of efficacy in patients who have experienced severe vomiting during earlier courses of cytotoxic therapy. Side effects consisting of mild sedation, diarrhoea and reversible extrapyramidal reactions have occurred, but are tolerated by many patients.

Clinical experience with atenolol in patients with chronic liver disease

The pharmacokinetics of atenolol were investigated following single intravenous (25 mg) and oral administration (100 mg) of atenolol in 13 patients with chronic liver disease and normal renal function and in 12 normal healthy volunteers. Four of the patients with chronic liver disease were not included in the statistical evaluation of kinetic data, since a reduction of creatinine clearance was observed during the course the study after ingestion of atenolol. A tendency to an increased distribution volume of atenolol could be observed in subjects with liver disease compared to normal volunteers. After intravenous and oral administration of atenolol, pharmacokinetic parameters such as elimination half-life, plasma clearance, and renal clearance did not differ significantly between patients with chronic liver disease and healthy volunteers. Thus, plasma half-life after intravenous dosing of atenolol was 6.0 +/- 0.46 hours in patients with hepatic disease and 5.0 +/- 0.4 hours in the controls, indicating absence of atenolol accumulation in hepatic failure. In the first days after starting beta-blocker therapy such as atenolol administration, parameters of kidney function as plasma creatinine, or possibly creatinine clearance, should be initially monitored at regular intervals, as there may be transient changes of renal function in patients with chronic liver disease, leading to delayed elimination of the drug.

Accumulation and adverse effects of metoprolol and propranolol after concurrent administration of cimetidine

Pharmacokinetics of metoprolol, propranolol and atenolol were investigated in six healthy volunteers following 7 days of oral monotherapy with these drugs and after 7 days concurrent administration of each of these betareceptor antagonists with cimetidine. Application of cimetidine did not lead to any interaction with atenolol, whereas mean peak plasma levels of metoprolol were increased by 70%, and those of propranolol by 95% due to concurrent administration of cimetidine (p less than 0.05). The AUC of the two last mentioned beta blockers behaved similarly (p less than 0.05). Measurement of exercise-induced tachycardia on the 6th day of administration showed no differences between monotherapy with the beta blocker and combined treatment with each of them and cimetidine. Except for one volunteer who complained of anxiety, weakness and sweating on the 6th day of cimetidine/metoprolol administration, no adverse effects could be observed during the combination therapy with cimetidine and the beta blockers or in monotherapy with beta blockers.

Influence of inflammatory disease on the clinical pharmacokinetics of atenolol and metoprolol

The influence of inflammatory disease on the pharmacokinetics of atenolol and metoprolol was investigated after administering single oral 100 mg doses of the drugs to six subjects. Each subject had a respiratory tract infection with an erythrocyte sedimentation rate (ESR) of over 20 mm in the first hour and a body temperature of at least 38.5 degrees. Since the subjects subsequently received atenolol and metoprolol when they were healthy, each person acted as his own control. Inflammatory disease had no influence on the kinetics of metoprolol. In contrast, mean peak plasma levels and AUC for atenolol were significantly lower, both by about 40 per cent, during infectious disease compared to the healthy state (p less than 0.05), where as renal clearance of atenolol slightly increased from 110.8 +/- 14.7 ml min-1 in the healthy state to 128 +/- 21.6 ml min-1, when the ESR's were elevated. The elimination half-life of atenolol, about 10 h, was not affected by the health status of the subjects. Reduced absorption in the gastro-intestinal tract and enhanced elimination of atenolol from plasma might account for the decreased AUC and peak plasma levels of the drug during inflammatory disease.

Interaction of metoprolol, propranolol and atenolol with concurrent administration of cimetidine

Pharmacokinetics of metoprolol, propranolol, and atenolol were investigated in six healthy volunteers following 7 days of oral monotherapy with these drugs, and after 7 days concurrent administration of each of these betareceptor antagonists with cimetidine. Application of cimetidine did not lead to any interaction with atenolol, whereas mean peak plasma levels of metoprolol were increased by 70%, and those of propranolol by 95% due to concurrent administration of cimetidine (P less than 0.05). The plasma level time curve (AUC) of the two above-mentioned beta blockers behaved similarly (P less than 0.05). Other kinetic parameters of these two drugs were not influenced to a statistically significant extent by cimetidine, despite the tendency for the elimination half-life of metoprolol and propranolol to be prolonged when cimetidine is added. Measurement of exercise-induced tachycardia on the sixth day of administration showed no differences between monotherapy with the beta blockers and combined treatment with each of them together with cimetidine. Apart from one volunteer who complained of anxiety, weakness, and sweating on the sixth day of cimetidine/metoprolol administration, no adverse effects could be observed during the combination therapy with cimetidine and the beta blockers, nor during monotherapy with beta blockers.

Variability of beta-blocker pharmacokinetics in young volunteers

Plasma concentrations of metoprolol, propranolol oxprenolol, acebutolol and its metabolite diacetolol were measured after single oral doses in young health volunteers. In order to assessed the inter- and intra-subject variability the following pharmacokinetic parameters were compared: AUC0(24), Cmax, tmax and t 1/2. The smallest variation in inter-subject variability was seen with oxprenolol and acebutolol: intrasubject variability was more uniform. Female volunteers taking an oral contraceptive generally had higher AUC0(24) and Cmax values than those not. This finding reached statistical significance only for metoprolol AUC0(24).