Cerebrospinal fluid concentrations of propranolol, pindolol and atenolol in man: evidence for central actions of beta-adrenoceptor antagonists

Effect of Propranolol on Motor Cortex Excitability in Essential Tremor: An Exploratory Study

Background

Essential tremor, the world's most prevalent movement disorder, lacks a clear understanding of its pathophysiology. Propranolol, a non-specific beta-blocker capable of crossing the blood-brain barrier, is a primary choice for essential tremor treatment. While its tremor-reducing effects are generally attributed to peripheral actions, various uses hint at central adrenergic effects. Nevertheless, propranolol's precise impact on the central nervous system in essential tremor subjects remains unexplored.

Methods

In this study, we employed transcranial magnetic stimulation to assess the influence of propranolol on the excitability of the primary motor cortex (M1) in patients with essential tremor, compared to an age- and sex-matched control group. Cortical excitability parameters were measured following placebo and propranolol administration, encompassing resting and active motor thresholds, motor evoked potential characteristics, cortical silent period, and the input/output curve.

Results

Distinct effects were observed across the two cortical hemispheres. Essential tremor patients displayed inhibition of the left M1 cortex and heightened excitability in the right M1 cortex four hours after propranolol administration, but not following placebo.

Conclusions

These findings suggest potential differential noradrenergic excitatory and inhibitory modulation. However, comprehensive understanding necessitates further investigations, including left-handed participants and more diverse essential tremor subpopulations. This study underscores the need for continued exploration to unravel propranolol's complex effects on motor cortex excitability in essential tremor.

In Vitro-In Vivo Correlation of Blood-Brain Barrier Permeability of Drugs: A Feasibility Study Towards Development of Prediction Methods for Brain Drug Concentration in Humans

PURPOSE

In vitro human blood-brain barrier (BBB) models in combination with central nervous system-physiologically based pharmacokinetic (CNS-PBPK) modeling, hereafter referred to as the "BBB/PBPK" method, are expected to contribute to prediction of brain drug concentration profiles in humans. As part of our ongoing effort to develop a BBB/PBPK method, we tried to clarify the relationship of in vivo BBB permeability data to those in vitro obtained from a human immortalized cell-based tri-culture BBB model (hiBBB), which we have recently created.

METHODS

The hiBBB models were developed and functionally characterized as previously described. The in vitro BBB permeabilities (Pe, × 10^-6 cm/s) of seventeen compounds were determined by permeability assays, and in vivo BBB permeabilities (Q_ECF) for eight drugs were estimated by CNS-PBPK modeling. The correlation of the Pe values with the Q_ECF values was analyzed by linear regression analysis.

RESULTS

The hiBBB models showed intercellular barrier properties and several BBB transporter functions, which were enough to provide a wide dynamic range of Pe values from 5.7 ± 0.7 (rhodamine 123) to 2580.4 ± 781.9 (rivastigmine). Furthermore, the in vitro Pe values of the eight drugs showed a good correlation (R² = 0.96) with their in vivo Q_ECF values estimated from human clinical data.

CONCLUSION

We show that in vitro human BBB models provide clinically relevant BBB permeability that can be used as input for CNS-PBPK modeling. Therefore, our findings will encourage the development of a BBB/PBPK method as a promising approach for predicting brain drug concentration profiles in humans.

A Practical Perspective on the Evaluation of Small Molecule CNS Penetration in Drug Discovery

The separation of the brain from blood by the blood-brain barrier and the bloodcerebrospinal fluid (CSF) barrier poses unique challenges for the discovery and development of drugs targeting the central nervous system (CNS). This review will describe the role of transporters in CNS penetration and examine the relationship between unbound brain (Cu-brain) and unbound plasma (Cu-plasma) or CSF (CCSF) concentration. Published data demonstrate that the relationship between Cu-brain and Cu-plasma or CCSF can be affected by transporter status and passive permeability of a drug and CCSF may not be a reliable surrogate for CNS penetration. Indeed, CCSF usually over-estimates Cu-brain for efflux substrates and it provides no additional value over Cu-plasma as the surrogate of Cu-brain for highly permeable non-efflux substrates. A strategy described here for the evaluation of CNS penetration is to use in vitro permeability, P-glycoprotein (Pgp) and breast cancer resistance protein efflux assays and Cu-brain/Cu-plasma in preclinical species. Cu-plasma should be used as the surrogate of Cu-brain for highly permeable non-efflux substrates with no evidence of impaired distribution into the brain. When drug penetration into the brain is impaired, we recommend using (total brain concentration * unbound fraction in the brain) as Cu-brain in preclinical species or Cu-plasma/in vitro Pgp efflux ratio if Pgp is the major limiting mechanism for brain penetration.

Relationship between Protein Binding and Extravascular drug Concentrations of a Water-soluble Drug, Cytosine Arabinoside

The degree of binding of a drug to plasma proteins has a marked effect on its distribution, elimination, and pharmacological effect. Since only the unbound fraction is available for distribution into extravascular space, the ratio of drug in cerebrospinal fluid (CSF) or saliva to that in plasma is often regarded as a physiological measure of the free fraction of a drug. CSF: plasma and saliva: plasma ratios of cytosine arabinoside (araC) have been measured in patients with acute leukaemia and found to be 0.1–0.28, implying a binding of 72–90%.

The protein binding of araC was measured by equilibrium dialysis in the plasma of patients with acute leukaemia at presentation. The mean binding ratio was 2.3 ± 6.8, implying that there was little or no protein binding. There was no correlation between alpha — 1 acid glycoprotein (AAG) levels and protein binding.

The low CSF and saliva: plasma araC ratios found, suggest that drugs such as araC which have low lipid solubility do not pass freely into extravascular space. Thus the CSF or saliva: plasma ratio cannot be considered a good physiological measure of protein binding for drugs with poor lipid solubility.

Improving the prediction of the brain disposition for orally administered drugs using BDDCS

In modeling blood-brain barrier (BBB) passage, in silico models have yielded ~80% prediction accuracy, and are currently used in early drug discovery. Being derived from molecular structural information only, these models do not take into account the biological factors responsible for the in vivo outcome. Passive permeability and P-glycoprotein (Pgp, ABCB1) efflux have been successfully recognized to impact xenobiotic extrusion from the brain, as Pgp is known to play a role in limiting the BBB penetration of oral drugs in humans. However, these two properties alone fail to explain the BBB penetration for a significant number of marketed central nervous system (CNS) agents. The Biopharmaceutics Drug Disposition Classification System (BDDCS) has proved useful in predicting drug disposition in the human body, particularly in the liver and intestine. Here we discuss the value of using BDDCS to improve BBB predictions of oral drugs. BDDCS class membership was integrated with in vitro Pgp efflux and in silico permeability data to create a simple 3-step classification tree that accurately predicted CNS disposition for more than 90% of 153 drugs in our data set. About 98% of BDDCS class 1 drugs were found to markedly distribute throughout the brain; this includes a number of BDDCS class 1 drugs shown to be Pgp substrates. This new perspective provides a further interpretation of how Pgp influences the sedative effects of H1-histamine receptor antagonists.

Adrenergic and serotoninergic receptors mediate the immunological activation of corticosterone secretion in male rats

In order to elucidate the mechanism of action of immune agents on corticosterone secretion, the present study evaluated the possible involvement of some neuronal pathways (serotoninergic, noradrenergic/adrenergic) in the lipopolysaccharide (LPS)-induced corticosterone release in male rats. Serotoninergic antagonists, mianserin (5-HT2C receptor blocker) or pindolol (5HT1A receptor blocker) or noradrenergic/adrenergic antagonists, prazosin (alpha 1-adrenoceptor blocker) or propranolol (beta-adrenoceptor blocker), were intraperitoneally (i.p.) injected before (5 min) the administration of LPS. In each experiment a group of rats i.p. injected with vehicle served as controls. Animals were sacrificed by decapitation 90 min after administration of LPS and trunk blood was collected for corticosterone radioimmunoassay. Results showed that pretreatment with mianserin, but not with pindolol, significantly reduced plasma corticosterone levels following administration of LPS (p < 0.05); prazosin attenuated the plasma corticosterone response to LPS (p < 0.05), while propranolol did not induce significant change. The present study indicated that serotoninergic and noradrenergic/adrenergic pathways are involved in the immunoneuroendocrine modulation of hypothalamus-pituitary-adrenal function in rats. In particular, it is probably mediated by the activation of 5-HT2C receptors and of alpha 1-adrenoceptors, while type 1A serotonin receptors or beta-adrenoceptors do not seem to be involved in such a phenomenon.

Changes in neurotransmitter sensitivity in the mouse neocortical slice following propranolol and theophylline administration

1. The mouse neocortical slice has been used to examine the sensitivity of neurones to isoprenaline, 5-hydroxytryptamine (5-HT) and adenosine acutely and following chronic treatment of animals with propranolol or theophylline. 2. While having little effect alone, all three agonists enhanced the d.c. depolarizing potential produced by N-methyl-D-aspartate (NMDA). The effect of (-)-isoprenaline (0.2 microM) was shared by (+)-isoprenaline at the much higher concentration of 10 microM. 3. Superfusion of slices with theophylline or 8-phenyltheophylline blocked responses to adenosine with evidence of selectivity. A single injection of theophylline 24 h before slice preparation did not alter agonist sensitivity, but when administered daily at 100 mg kg-1 for 14 days, the xanthine caused a loss of sensitivity to adenosine and (-)-isoprenaline but not 5-HT. The lower dose of theophylline, 10 mg kg-1 daily, also led to a loss of adenosine responses but no change of sensitivity to the amines. 4. Following the 14 day treatment with theophylline at 100 mg kg-1 daily in two groups of mice, responses to adenosine recovered to control levels after 20 days. 5. Propranolol superfusion blocked responses to both isomers of isoprenaline and 5-HT but did not affect sensitivity to adenosine. 6. Chronic treatment with propranolol at 25 mg kg-1 daily for 14 days induced a loss of sensitivity to (-)-isoprenaline and 5-HT but not adenosine. A lower dose of 5 mg kg-1 daily caused no change in responses to adenosine or 5-HT, but yielded an increased sensitivity to (-)-isoprenaline. 7. The results are discussed with respect to reports of receptor up-regulation in binding studies; caution is clearly required in extrapolating from such work to receptor activity in a functional system, especially in the case of theophylline and adenosine.

Critical factors of intracerebral microdialysis as a technique to determine the pharmacokinetics of drugs in rat brain

The purpose of this investigation was to determine the effect of experimental conditions on the concentrations of atenolol and acetaminophen in brain microdialysate, and to investigate the feasibility of performing repeated experiments within individual rats. Following intravenous bolus administration, reproducible concentration-time profiles were obtained in plasma and in brain dialysate. Based on corrections for in vitro recoveries of the intracerebral probe, the estimated ratio of the AUC in brain extracellular fluid (AUCbrain ECF) over the AUC in plasma (AUCplasma) +/- S.E.M. was 3.8 +/- 0.6% (n = 6) for atenolol and 18 +/- 2% (n = 6) for acetaminophen. Upon intracerebroventricular administration, interanimal differences in kinetics of acetaminophen in brain dialysate were observed while the concentrations of atenolol were below the detection limit of the assay. The influence of the use of isotonic versus hypotonic perfusate solutions on AUCbrain ECF values after intravenous bolus administration of both drugs was determined. Repeated experiments with the isotonic perfusate (24, 48 and 78 h post-surgery) resulted in AUCbrain ECF values with the ratio of 100: 98: 76% for acetaminophen and 100: 103: 98% for atenolol. Using a hypotonic perfusion solution the ratio of AUCbrain ECF values was 100: 154: 114% for acetaminophen and 100: 378: 427% for atenolol. A clear effect of the temperature of the hypotonic perfusate (24 vs 38 degrees C) on acetaminophen AUCbrain ECF values was revealed. The ratio of AUCbrain ECF values obtained at 24: 38 degrees C was 192: 100%.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychomotor performance and antihypertensive treatment

1. The aim of treatment of hypertension is prevention of cardiovascular complications without adverse drug reactions. Psychomotor performance can be measured objectively yet there remains uncertainty concerning the psychomotor effects of antihypertensive drugs during chronic treatment. This uncertainty is partly due to the confounding adverse effects of cerebrovascular disease and hypertension itself. There are as yet insufficient good quality data on psychomotor effects with which to differentiate between the commonly used agents. However, in general, the beneficial effect of lowering blood pressure tends to more than offset any adverse effects of the agent used.

Receptor occupancy in lumbar CSF as a measure of the antagonist activity of atenolol, metoprolol and propranolol in the CNS

1. The antagonist activity of atenolol, metoprolol and propranolol in the CNS was estimated by determining the extent to which the drugs occupy animal beta 1- and beta 2-receptors in CSF ex vivo at the time of lumbar puncture. 2. Five CSF and plasma samples were obtained 4 h after drug intake from subjects treated for hypertension with atenolol, 100 mg once daily and five from subjects treated with metoprolol, 50 mg three times daily. Twenty-four samples were obtained 1, 2, 4 or 12 h after drug intake from subjects receiving a single 40 mg dose of propranolol. 3. The receptor occupancy in the samples was determined by adding beta 1-receptors of rabbit lung and beta 2-receptors of rat reticulocytes into the samples and labeling the receptors with a nonselective beta-adrenoceptor antagonist, (-)-[3H]-CGP-12177. 4. Atenolol and metoprolol occupied, as expected, larger fractions of beta 1- than beta 2-receptors in CSF and plasma samples. The receptor fraction occupied by atenolol in CSF was significantly (P < 0.05) lower than that occupied by metoprolol. The differences in occupancy between the drugs in plasma, however, were not statistically significant. 5. Propranolol occupied larger fractions of beta 2- than beta 1-receptors in the samples. Although propranolol concentrations in CSF were only 1/20-1/40 of those in plasma, the receptor occupancy of propranolol in CSF was similar to that in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic administration of atenolol on the in situ perfused mesentery of normotensive and hypertensive rats

1. Atenolol 50 mg kg-1 was administered daily for 7 to 21 days to male normotensive Wistar rats and to Okamoto spontaneously hypertensive rats. Blood pressure and heart rate were monitored daily. 2. Following atenolol treatment the response to exogenous noradrenaline and to periarterial nerve stimulation was measured in the in situ blood perfused mesentery. 3. In normotensive animals, treatment with atenolol for 7 days had little effect on the responses of the mesenteric vasculature to either exogenous noradrenaline or to periarterial nerve stimulation. After 21 days, the response to noradrenaline was little changed, but there was a statistically significant decrease in the response to periarterial nerve stimulation at the higher stimulation frequencies (16 and 35 Hz). 4. In spontaneously hypertensive animals, treatment with atenolol for 7 days did not significantly affect the response of the mesenteric vasculature to either noradrenaline or periarterial nerve stimulation; however, after treatment for 21 days, responses to exogenous noradrenaline were reduced, while responses to periarterial nerve stimulation were even more markedly reduced, particularly at the lower stimulus frequencies. 5. The time course of the observed effects suggests that, over time, atenolol induces changes other than the simple blockade of beta-adrenoceptors which can be demonstrated to be present immediately. The decreased responses to periarterial nerve stimulation in normotensive and hypertensive animals suggest that the changes induced affect presynaptic mechanisms of noradrenaline release (either directly or indirectly), rather than changes in postsynaptic receptor sensitivity or vascular reactivity. The observation that the changes are more evident in hypertensive animals indicates that they may play an important role in the antihypertensive action of atenolol.

Permeability of the blood-brain barrier for atenolol studied by positron emission tomography

The permeability of the blood-brain barrier for atenolol, a hydrophilic beta-adrenergic blocking agent, has been assessed in dogs, by studying the distribution of [11C]atenolol in brain tissue with positron emission tomography. The passage of atenolol into the brain was very limited, but a measurable small net influx into the brain tissues did occur. Osmotic opening of the blood-brain barrier resulted in a marked increase of the atenolol concentrations in brain tissue. The approach described, with sequential non-invasive measurements in brain tissue, is applicable to pharmacokinetic studies of atenolol in man.

The effect of theophylline on essential tremor: the possible role of GABA

The chronic administration of theophylline was studied in twenty patients with essential tremor in a double-blind cross-over trial. The tremor was improved significantly after four weeks of treatment. In mice the chronic administration of theophylline was compared with propranolol on the modulation by adenosine, 5-HT, (-)isoprenaline or GABA of NMDA-induced depolarisation of neocortical slices. Adenosine depolarisation was abolished by two-weeks treatment with theophylline but not propranolol. Potentiation by (-)isoprenaline of NMDA responses was reduced by theophylline (100 mg/kg/day) and propranolol treatment (25 mg/kg/day), but a lower dose of propranolol further increased it. The enhancement by 5-HT of NMDA-induced depolarisation was unaffected by the pretreatment with theophylline, while the higher dose of propranolol blocked it. GABA caused no significant change of NMDA depolarisation in control slices, but after theophylline treatment (100 mg/kg/day) and propranolol administration at both doses it significantly potentiated NMDA depolarisation. The enhancement of GABA sensitivity might be an important common factor in decreasing the essential tremor after propranolol and theophylline treatment.

Studies on active transport of (E)-10-hydroxynortriptyline in the kidney and brain of rats: effects of propranolol and quinidine

Studies in humans have given strong support of an active transport of (E)-10-hydroxynortriptyline [E)-10-OH-NT) in the kidney and from the cerebrospinal fluid. After 3 days of intraperitoneal injections of (E)-10-OH-NT (10 mg/kg t.i.d.) in a rat model, we investigated the effect of propranolol and quinidine (25 and 2.5 mg/kg injected 6 times during day 3) on the concentrations of (E)-10-OH-NT in urine, plasma (total and unbound) and brain. In a group of control rats the renal clearance of (E)-10-OH-NT varied 10-fold between rats, but was reproducible from Day 2 to Day 3 (r = 0.83; n = 8; p less than 0.05). Quinidine markedly decreased the renal clearance of both total and unbound (E)-10-OH-NT from plasma, while the effect of propranolol was less pronounced. There was no difference in the ratio of (E)-10-OH-NT concentrations in brain and plasma (unbound) between treated and control rats. We conclude that (E)-10-OH-NT is actively secreted in the rat proximal tubule and that the activity of this system varies between rats, but is constant in the individual rat. Quinidine, and to a less extent propranolol, inhibits this renal secretion. By the present methodology we could not demonstrate an active transport of (E)-10-OH-NT from brain to blood in the rat. Studies using other methods are needed to further elucidate this.

Stereoselective efflux of (E)-10-hydroxynortriptyline enantiomers from the cerebrospinal fluid of depressed patients

In 5 patients treated with nortriptyline or amitriptyline for at least 9 months, the cerebrospinal fluid (CSF)/plasma ratio for 10-hydroxynortriptyline (10-OH-NT) ranged from 0.085 to 0.172, which is similar to the ratio previously measured in patients treated for 3 weeks. In 4 other patients treated with racemic (E)-10-OH-NT, the mean concentration ratio between (-)- and (+)-(E)-10-OH-NT was 3.56 in plasma, 2.39 in plasma ultrafiltrate and 1.42 in CSF (one-way ANOVA; P less than 0.001). The mean free fraction in plasma determined by ultrafiltration for (-)-(E)-10-OH-NT was 28.9 +/- S.D.1.1% and for the (+)-enantiomer 43.7 +/- 0.8% (P less than 0.001) confirming the difference in protein binding shown previously in healthy subjects. There was a correlation between the concentration of 10-OH-NT (sum of enantiomers) in CSF and plasma ultrafiltrate (r = 0.96; n = 7; P less than 0.001). The concentration in CSF was, however, only about 50% of that in the plasma ultrafiltrate and this seems to be due to a stereoselective transport of (E)-10-OH-NT out from the CSF. The secretion from the CSF is more pronounced for the (-)-compared to the (+)-enantiomer, which is consistent with the stereoselectivity of the renal secretion of these compounds.

Side effects of beta-blocker treatments as related to the central nervous system

During the last decade beta-adrenoceptor antagonists have become one of the first-line treatments for hypertension. Generally, they have been shown to be safe with a low frequency of serious side effects. However, minor subjective symptoms, usually considered to be CNS-related, have been reported for all beta-blockers used. Thus, all beta-blockers on the market seem to have a high benefit:risk ratio; independent of their physicochemical properties and pharmacodynamic profile, however, they seem to cause CNS-related side effects to about the same extent. These minor side effects, the mechanisms of which are unclear, consist of subtle effects on general well being, decreased initiative, a depressed frame of mind, and disturbed sleep. Generally, however, beta-blockers in therapeutic dosages do not affect the qualitative functions of the brain. The results so far available have been obtained primarily by using objective methods. Further comparison has now been initiated using documented subjective methods to investigate whether the objectively documented differences are of any clinical relevance to the patient's quality of life. Although it cannot be claimed with certainty, nonselective beta-blockers seem to cause CNS-related side effects to a greater extent than beta 1-selective blockers. Differences in the degree of hydrophilicity of the beta-blocker are apparently of no clinical relevance in this respect. Rather, the plasma concentration of the beta-blocking drug (degree of beta-blockade) seems to be the major determinant of whether or not CNS-related symptoms appear in susceptible patients.

Beta-blockers and central nervous system side effects

Beta-adrenergic blocking drugs are a widely used, well tolerated and effective treatment for a variety of cardiovascular and noncardiovascular disorders. Over the years, beta-blockers have been associated with an incidence, albeit low, of CNS side effects. The question of interest, however, is whether the incidence is the same for all members of the class or whether other properties, such as hydrophilicity, have a bearing on the incidence of this type of side effect? This article addresses this question. In pharmacokinetic terms the lipophilic beta-blockers have been shown, both in animals and man, to readily cross the blood-brain barrier in contrast to hydrophilic beta-blockers. This is thought to have possible clinical relevance with respect to the relative incidence of CNS side-effects. To clarify the situation every published clinical paper, in which the beta-blockers propranolol (highly lipophilic, nonselective, no intrinsic sympathomimetic activity (ISA)), pindolol (moderately lipophilic, nonselective, moderate ISA), metoprolol (moderately lipophilic, beta 1-selective, no ISA) and atenolol (hydrophilic beta 1-selective, no ISA) were compared, was assessed for information pertaining to CNS side effects. This comprehensive review of the literature has shown, with few exceptions, that the incidence of CNS side effects such as sleep disturbances, dreaming, nightmares and hallucinations following clinically accepted doses of the four beta-blockers under scrutiny is generally low and that effects on short-term memory are minimal or absent. However, within this group of four drugs the incidence of these side effects is lowest with hydrophilic atenolol and generally highest with pindolol and propranolol. Metoprolol occupies an intermediate position. This order is in agreement with the pharmacokinetic observation that the more hydrophilic the molecule, the less is found in the brain tissue of both animals and man, although in the case of pindolol other factors may be important. The clinical relevance of studies involving psychometric testing is not clear.

Nonlinear distribution of atenolol between plasma and cerebrospinal fluid

Long Evans rats were given atenolol doses ranging from 0.27 to 5.4 mg/kg by intraperitoneal injection Animals were dosed once every 2 hr for a total of five doses. Atenolol concentrations 1 hr after the last dose were measured from simultaneously obtained plasma and cerebrospinal fluid (CSF) samples CSF concentrations of atenolol were not proportional to plasma concentrations. The ratio of CSF/plasma concentrations was higher (0.33) at lower plasma atenolol levels (less than 100 ng/ml) than at the higher atenolol plasma levels (0.05) (P less than 0.001). The relationship between plasma and cerebrospinal fluid atenolol concentrations was best described by the sum of a Michaelis-Menten and linear function. Animals were also given atenolol doses and then subjected to global cerebral ischemia. The relationship of atenolol concentrations from plasma and CSF in these animals was linear, with a constant partition ratio of 0.02. Together these data show that atenolol partitioning between plasma and CSF is nonlinear and possibly an energy-dependent process.

Central effects of drugs used in migraine prophylaxis evaluated by visual evoked potentials

The present study used recordings of visual potentials evoked by pattern reversal (VEPs) to investigate the central effects of three drugs used in migraine prophylaxis: the calcium channel blocker nifedipine, the beta-1-selective blocker metoprolol, and the nonselective beta adrenoreceptor blocker propranolol. The study involved 58 patients with common or classical migraine who were treated in a double-blind randomized study over a period of 7 months, while the effectiveness of prophylactic treatment was recorded in headache diaries that were subjected to time series analysis. VEPs were recorded at the beginning of a 2-month baseline period without treatment, after 4 months of treatment, and at the end of a 3-month washout period. At baseline, migraine patients had significantly higher VEP amplitudes and longer latencies than did a group of 87 healthy control subjects. Patients were separated by statistical analysis into responders and nonresponders to each prophylactic treatment. Nifedipine had no effects on the frequency, intensity, and duration of migraine attacks, nor on amplitude and latency of the VEPs. In contrast, the use of beta blockers resulted in a significant decrease in VEP amplitude, both in responders and nonresponders, whereas VEP latency remained unchanged. VEP amplitudes returned to the initial values at follow-up in the nonresponders, but stayed at lower levels in responders. Beta blockers thus appear to have a significant effect on the increased excitability of the visual system in patients with migraine, although their action is not directly related to their reduction of migraine frequency.

Psychiatric and neuropsychological response to propranolol in Graves' disease

We describe the endocrine, psychiatric, and neuropsychological assessments of 10 untreated, newly diagnosed Graves' disease subjects who were studied longitudinally at three stages: hyperthyroid (stage 1), after 2 weeks of propranolol treatment (stage 2), and after 6 months of antithyroid treatment (stage 3). Major depression, generalized anxiety disorder, and hypomania were diagnosed at stage 1. Elevations on psychiatric symptom rating scales and in motor activity monitoring at stage 1 were significantly decreased at stage 2 and again at stage 3. Psychiatric improvements paralleled improvements in endocrine symptoms. Neuropsychological improvements were noted on the more challenging memory and attention tasks at stage 3, whereas propranolol treatment was not associated with changes on attention tests. Results are discussed in relation to catecholamine-thyroid hormone interactions, in particular, the beta-adrenergic system.

The pharmacokinetics of lignocaine and beta-adrenoceptor antagonists in patients with acute myocardial infarction

Lignocaine (lidocaine) and beta-adrenoceptor antagonists are widely used after acute myocardial infarction. The therapeutic value of these agents depends on the achievement and maintenance of safe and effective plasma concentrations. Lignocaine pharmacokinetics after acute myocardial infarction (MI) are controlled by a number of variables. The single most important is left ventricular function, which affects both volume of distribution and plasma clearance. Other major factors include bodyweight, age, hepatic function, the presence of obesity, and concomitant drug therapy. Lignocaine is extensively bound to alpha 1-acid glycoprotein, a plasma protein which is also an acute phase reactant. Increases in alpha 1-acid glycoprotein concentration occur after an acute MI, decreasing the free fraction of lignocaine in the plasma and consequently decreasing total plasma lignocaine clearance without altering the clearance of non-protein-bound lignocaine. Complex changes in lignocaine disposition occur with long term infusions, and therefore early discontinuation of lignocaine infusions (within 24 hours) should be undertaken whenever possible. Because the risk of ventricular tachyarrhythmia declines rapidly after the onset of an acute MI, lignocaine therapy can be rationally discontinued within 24 hours in most patients. Lignocaine has a narrow toxic/therapeutic index, so that pharmacokinetic factors are critical in dose selection. In contrast, beta-adrenoceptor antagonists' adverse effects are more related to the presence of predisposing conditions (such as asthma, heart failure, bradyarrhythmias, etc.) than to plasma concentration. The pharmacokinetics of beta-adrenoceptor antagonists are important to help assure therapeutic efficacy, to provide information about the anticipated time course of drug action, and to predict the possible role of ancillary drug effects (such as direct membrane action) and loss of cardioselectivity. Lipid solubility is the main determinant of the pharmacokinetic properties of a beta-adrenoceptor antagonist. Lipid-soluble agents like propranolol and metoprolol are well absorbed orally, and undergo rapid hepatic metabolism, with important presystemic clearance and a short plasma half-life. Water-soluble drugs like sotalol, atenolol, and nadolol are less well absorbed, and are eliminated more slowly by renal excretion. Clinical assessment of beta-adrenoceptor antagonism is more valuable than plasma concentration determinations in evaluating the adequacy of the dose of a particular beta-adrenoceptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipophilicity, hydrophilicity, and the central nervous system side effects of beta blockers

One of the attributes of beta-adrenergic blocking agents that has distinguished these drugs from each other is degree of lipophilicity. While this feature may play a role in facilitating passage across the blood-brain barrier, it is essential to realize that crossing the barrier is not necessarily synonymous with the ability to cause central nervous system (CNS) effects. Several studies have found some degree of CNS side effects, particularly tiredness and fatigue, with atenolol, a hydrophilic beta blocker. Pindolol, a moderately lipophilic beta blocker, has been reported to cause greater disturbances on electroencephalogram (EEG) than propranolol, the most highly lipophilic beta blocker. The investigational agent bevantolol exhibits a moderate degree of lipophilicity and a low frequency of CNS side effects. Drug-induced increases in plasma catecholamine levels, the possible saturation of CNS receptor sites at relatively low drug levels, and the specific structural details of beta-blocker molecules have been suggested as possible contributory factors in determining the degree of CNS effects.

Beta blockers and the central nervous system

The exact mechanism of action of beta blockers in migraine remains undetermined. An effect on the central nervous system (CNS) might be a factor. The evidence from the literature indicates that the anatomical and chemical targets for these drugs are present in the mammalian brain, that they readily penetrate the brain, and that they may modify CNS functions. The present study shows that psychomotor tests and contingent negative variation (CNV), an event related slow cerebral potential, both of which are abnormal in untreated migraineurs, tend to normalize after treatment with the beta blocker metoprolol. Moreover, a strong positive correlation was found between the amplitude of CNV and the clinical efficacy of beta blockers in migraineurs. One might hypothesize that a hyperactive central catecholaminergic state in migraine might be the common denominator between reduced performance on psychomotor testing and enhanced CNV. It remains to be determined whether this is due to hyperactivity of catecholaminergic neurons or to hypersensitivity of catecholamine receptors.

Acebutolol in essential hypertension: results of two multicenter studies against placebo and propranolol

Two double-blind multicenter studies compared acebutolol with placebo (acebutolol, N = 121; placebo, N = 116) and with propranolol (acebutolol, N = 186; propranolol, N = 190) in essential hypertension. Acebutolol significantly reduced mean sitting diastolic blood pressure from 99.2 +/- 0.3 mm Hg at baseline to 89.1 +/- 0.9 mm Hg at the end of dose titration (p = 0.001). Significantly more acebutolol patients (65%) achieved therapeutic goal than did placebo patients (28%, p less than 0.01). The reduction in heart rate in acebutolol-treated patients (9.2 bpm) was greater than in placebo-treated patients (1.2 bpm, p = 0.001). The incidence of side effects and the number of patients discontinued because of side effects did not significantly differ between acebutolol and placebo. Acebutolol and propranolol produced comparable reductions in diastolic, systolic, and mean arterial blood pressures (p less than 0.001). At equipotent doses the 13% decrease in heart rate in patients receiving acebutolol was significantly less than the 17% decrease in propranolol patients (p = 0.02). The number of patients experiencing central nervous system (CNS) side effects while receiving acebutolol (N = 50) was significantly less than with propranolol (N = 75, p = 0.001), and significantly fewer acebutolol patients (N = 11) were discontinued because of side effects compared with propranolol patients (N = 29, p less than 0.01). Laboratory, ECG, or chest X-ray results did not differ for acebutolol, placebo, or propranolol. Acebutolol appears to be safe and effective in the management of mild to moderately severe essential hypertension and is better tolerated than propranolol in terms of CNS side effects, with a significantly lesser effect on heart rate.

Clinical consequences of the lipophilicity and plasma protein binding of antiarrhythmic drugs and active metabolites in man

In two series of antiarrhythmic drugs tested, as the octanol/water partition coefficient increases so do the following: elimination from the body by biotransformation, first-pass biotransformation in the liver and gastrointestinal tract after oral administration, protein binding to some extent, and penetration into brain tissue. Patients receiving lipophilic beta-adrenoreceptor blocking drugs may experience more central nervous system side effects than those receiving hydrophilic beta blockers. Structural modification of a drug, guided by the concept of bioisosterism, may allow the disassociation of therapeutic from toxic activities. Alpha-1 acid glycoprotein is the major plasma protein that binds the basic antiarrhythmic drugs. Antiarrhythmic drug metabolites are generally more polar (less lipophilic) and less plasma protein-bound than the parent drugs.

Inhibition of synaptosomal [3H]noradrenaline uptake by beta-adrenoceptor blocking drugs: influence of lipophilicity

Ten beta-adrenoceptor blocking drugs varying in lipophilicity and beta-adrenoceptor blocking potency were examined for inhibitory effects on synaptosomal [3H]noradrenaline uptake. All compounds produced a concentration-dependent inhibition of noradrenaline uptake, but were at least one order of magnitude less potent than desmethylimipramine and cocaine. The order of potency was pronethalol greater than propranolol greater than betaxolol greater than alprenolol greater than oxprenolol greater than practolol greater than metoprolol greater than acebutolol greater than sotalol greater than atenolol, with IC50 values ranging from 4.0 X 10(-6) to 2.2 X 10(-3) M. Uptake inhibition was unrelated to beta-adrenoceptor blocking potency, but was highly correlated with drug lipophilicity. (+)-Propranolol was an effective uptake inhibitor, as was the local anaesthetic procaine. Kinetic analysis of uptake inhibition by propranolol, oxprenolol, metoprolol and procaine revealed a mixed inhibition for all four agents examined. It is suggested that this effect of beta-adrenoceptor blockers may be mediated, at least in part, by an action on membrane phospholipids associated with the noradrenaline carrier protein, and that noradrenaline uptake inhibition may underlie certain central side-effects observed with some drugs in this group.

Liquid chromatographic retention of beta-adrenoceptor antagonists: an index of lipid solubility

The in-vitro lipophilicity of nine beta-adrenoceptor antagonists was evaluated based on retention on a reverse-phase C-18 high-pressure liquid chromatographic (hplc) system at physiologic pH. Propranolol was by far the most lipophilic drug, while atenolol and sotolol were the least. Hplc retention was highly correlated (r = 0.92) with octanol: buffer partition coefficient. Thus hplc retention is a rapid and replicable approach to the determination of in-vitro lipophilicity that does not require radioactive drug.

Exercise-induced increments in plasma levels of propranolol and noradrenaline

Exercise-induced changes in the plasma levels of propranolol and noradrenaline were determined in nine volunteers. Total plasma propranolol levels were increased during submaximal treadmill exercise, with exercise-induced increments of 13 +/- 4% at 4 h after the last dose, 18 +/- 7% at 9 h and 41 +/- 5% at 16 h. Exercise-induced increments in plasma propranolol were observed after single as well as repeated doses. During exercise, increments in plasma propranolol were correlated temporally with changes in plasma noradrenaline. Exercise-induced increments in plasma noradrenaline were greater during propranolol administration than during placebo periods. The changes in plasma propranolol concentration during exercise may reflect a redistribution of propranolol at its site(s) of action.

Attempt at pharmacological differentiation of central beta-adrenergic receptors

The beta-adrenergic stimulants isoprenaline, salbutamol and clenbuterol decreased motor activity, reduced the interest of fasting mice in food pellets ('Tantale' test), and antagonized high-dose apomorphine hypothermia. Clenbuterol was 16--60 times more potent than the other two agonists in all tests, apparently because of better crossing into the C.N.S. The beta-adrenergic blockers, d,l-propranolol and l-penbutolol, completely antagonized the effects of salbutamol and clenbuterol in tests of motor activity and apomorphine hypothermia, penbutolol being 30--60 times more active than propranolol, perhaps due to its greater lipid solubility. The Tantale test allows unambiguous differentiation between penbutolol and propranolol. While the first completely blocked the effects of clenbuterol and salbutamol, the second was effective only within a narrow dose range. Finally, the dose-effect relationships of the 3 agonists were parallel in the Tantale test, while they were divergent in the other two. This suggests that different classes of beta-adrenergic receptors may be involved in the various test.

Atenolol vs. propranolol in essential tremor. A controlled, quantitative study

The beta-1 selective, hydrophilic adrenoceptor blocking drug atenolol (100 mg daily) was compared to the non-selective, lipid-soluble beta-blocker propranolol (240 mg daily), and to placebo, in a double-blind cross-over study in 24 patients with essential tremor. Atenolol and propranolol caused a similar decrease in heart rate. Both beta-blockers also suppressed the tremor intensity; there was no significant difference between them, but both were significantly better than placebo. These drugs did not affect tremor frequency. Twelve of the patients preferred propranolol subjectively, one preferred atenolol and none preferred placebo. No marked side-effects were observed. It was concluded that atenolol and other cardio-selective blockers offer an alternative for patients unable to tolerate the non-selective drugs. The site of action and receptor sub-type involved have still to be determined.

Clinical pharmacokinetics of cerebrospinal fluid

The distribution of drugs into the cerebrospinal fluid has long been considered a challenging field of investigation in 2 major respects: (a) understanding how the physicochemical properties (molecular weight, pKa, plasma protein binding) of various molecules influence their movements across such a specific structure as the blood-brain barrier; and (b) defining the relationship between cerebrospinal fluid concentrations of various drugs and their central (side) effects. An attempt has been made to review the very dispersed information presently available to offer a clinically orientated picture of this area of pharmacokinetics. Drugs acting on the central nervous system (benzodiazepines, tricyclic antidepressants, anticonvulsants, opioids), antibacterial agents, cardiovascular drugs (beta-adrenoceptor blockers and digoxin), antineoplastic drugs (mainly methotrexate), and other miscellaneous agents (corticosteroids, cimetidine, methylxanthines) are reviewed. The available evidence seems to support the conclusion that only for methotrexate and antibacterial agents does knowledge of cerebrospinal fluid pharmacokinetics have direct therapeutic implications, while the mosaic of information available for other drugs does little more than provide a partially satisfactory picture.

Pindolol: a review of its pharmacology, pharmacokinetics, clinical uses, and adverse effects

Pindolol is a new noncardioselective beta adrenergic blocking agent with intrinsic sympathomimetic activity. In the treatment of mild to moderate hypertension, pindolol provides effective control of blood pressure in a large majority of patients when administered alone or, more commonly, when combined with a thiazide diuretic. Pindolol is approximately as effective as propranolol in the therapy of hypertension, but in some crossover trials central nervous system side effects were more frequent with pindolol. A "ceiling effect" may be observed as dosages are titrated upward above approximately 20 to 30 mg per day, such that further blood pressure reductions may not be achievable. Some patients will exhibit a paradoxical increase in blood pressure with an increase in dosage. In patients who respond to modest doses of pindolol, twice or even once daily dosing is often adequate. This prolonged duration of hypotensive activity, while not suggested by the kinetics of this or similar drugs, is probably common to most beta blockers. Investigations in small numbers of patients with angina pectoris have reported variable but generally beneficial results with pindolol.