Esmolol. A review of its therapeutic efficacy and pharmacokinetic characteristics

Esmolol is an ultra short-acting intravenous cardioselective beta-antagonist. It has an extremely short elimination half-life (mean: 9 minutes; range: 4 to 16 minutes) and a total body clearance [285 ml/min/kg (17.1 L/h/kg)] approaching 3 times cardiac output and 14 times hepatic blood flow. The alpha-distribution half-life is approximately 2 minutes. When esmolol is administered as a bolus followed by a continuous infusion, onset of activity occurs within 2 minutes, with 90% of steady-state beta-blockade occurring within 5 minutes. Full recovery from beta-blockade is observed 18 to 30 minutes after terminating the infusion. Esmolol blood concentrations are undetectable 20 to 30 minutes postinfusion. The elimination of esmolol is independent of renal or hepatic function as it is metabolised by red blood cell cytosol esterases to an acid metabolite and methanol. The acid metabolite, which is renally eliminated, has 1500-fold less activity than esmolol. Methanol concentrations remain within the range of normal endogenous levels. Clinically, esmolol is used for the following: (i) situations where a brief duration of adrenergic blockade is required, such as tracheal intubation and stressful surgical stimuli; and (ii) critically ill or unstable patients in whom the dosage of esmolol is easily titrated to response and adverse effects are rapidly managed by termination of the infusion. In adults, bolus doses of 100 to 200mg are effective in attenuating the adrenergic responses associated with tracheal intubation and surgical stimuli. For the control of supraventricular arrhythmias, acute postoperative hypertension and acute ischaemic heart disease, doses of < 300 micrograms/kg/min, administered by continuous intravenous infusion, are used. The principal adverse effect of esmolol is hypotension (incidence of 0 to 50%), which is frequently accompanied with diaphoresis. The incidence of hypotension appears to increase with doses exceeding 150 micrograms/kg/min and in patients with low baseline blood pressure. Hypotension infrequently requires any intervention other than decreasing the dose or discontinuing the infusion. Symptoms generally resolve within 30 minutes after discontinuing the drug. In surgical and critical care settings where clinical conditions are rapidly changing, the pharmacokinetic profile of esmolol allows the drug to provide rapid pharmacological control and minimises the potential for serious adverse effects.

Quantification of an 11C-labelled beta-adrenoceptor ligand, S-(-)CGP 12177, in plasma of humans and rats

beta-Adrenoceptors in human lungs and heart can be imaged with the radioligand 4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3- dihydro-2H-benzimidazol-2-11C-one (CGP 12177, [11C]I). For quantification of receptor density with compartment models by adjustment of rate constants, an 'input function' is required which consists of the integral of the concentration of unmodified ligand in arterial plasma over time. A discrepancy in the literature regarding metabolic stability of [11C]I prompted us to study metabolism in rats by reversed-phase HPLC (RP-HPLC) of trichloroacetic acid extracts of arterial plasma after i.v. injection of [11C]I (> 11.1 TBq/mmol, 11 MBq/kg). Some plasma samples were also directly applied to an internal-surface reversed-phase (ISRP) column. In parallel experiments, tritiated [11C]I was employed and methanol extracts of arterial plasma were analyzed by straight-phase TLC. The three methods were in excellent agreement. Unmodified [11C]I decreased from > 98.5% (3H) or > 99.9% (11C) initially to 57 +/- 7% at 80 min post injection due to formation of two polar metabolites. Using the RP-HPLC method, no metabolism was detectable in humans up to 30 min after injection of [11C]I (1851 MBq). Deproteinization of plasma with acetonitrile resulted in the formation of a radioactive species (artifact) which eluted immediately after the void volume in RP-HPLC and which could be mistakenly interpreted as a metabolite. Plasma protein binding was low (ca. 30%) in both humans and rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive treatment with a vasodilating beta-blocker, carvedilol, in chronic hemodialysis patients

Carvedilol is an antihypertensive agent which displays unselective beta-blocking, alpha 1-blocking and antioxidant properties. It is primarily metabolized by the liver and excreted via the biliary system. The compound is highly lipophilic and strongly bound to plasma proteins. Consequently, there is no elimination during hemodialysis. The efficacy, safety, and pharmacokinetic profile of carvedilol titrated to effect were investigated in an open clinical trial in 15 long-term hemodialysis patients with arterial hypertension over a period of 12 weeks. The drug was administered only on days without dialysis. After a wash-out phase of one week, carvedilol was started in a dose of 12.5 mg per day. All 15 patients were titrated according to the antihypertensive effect to a daily dose of 25 mg of carvedilol. Carvedilol was effective in lowering blood pressure in hemodialysis patients (RR systolic: 170 +/- 11 vs. 144 +/- 9 mmHg; RR diastolic: 98 +/- 10 vs. 85 +/- 10 mmHg). The pharmacokinetic parameters of carvedilol and its active metabolite M2, assessed in 12 of the 15 patients, were not influenced by the lack of renal function or intermittend haemodialysis. In particular, there was no accumulation of carvedilol or its metabolite M2. In terms of side effects, three patients had to be withdrawn from the trial, because of hypoglycemia (n = 1), insufficient blood pressure control (n = 1) and prolonged hypotension (n = 1). Taken together, these results indicate that carvedilol is a safe and efficacious antihypertensive agent which can be used in patients maintained by maintenance dialysis treatment.

[A pharmacokinetic study of korinfar-retard in monotherapy and in combination with cordanum and triampur in patients with arterial hypertension]

The long-acting corinfar formulation, corinfar-retard tablets, 20 mg (AWD, Germany), was studied for pharmacokinetics in single and course use in 40 patients with arterial hypertension, as well as for its effects of cordanum and triampur. Patients' plasma corinfar was measured by high performance liquid chromatography. There were no changes in the pharmacokinetics of the agent when it was used in its course use. Cordanum and triampur was demonstrated to have no effects on the pharmacokinetics of corinfar during their application.

Pharmacodynamics and pharmacokinetics of esmolol, a short-acting beta-blocking agent, in children

Esmolol, a short-acting intravenous cardioselective beta-blocking agent, was evaluated for age-dependent pharmacodynamic and pharmacokinetic features in 17 young patients (6 months to 14 years). A loading dose (500 micrograms/kg/min) alternating with a maintenance dose (25-200 micrograms/kg/min, titrating by 25 micrograms/kg/min every 4 min) was infused until the heart rate or mean arterial pressure decreased 10%. Cardiac index, left ventricular shortening fraction, and systemic vascular resistance were measured at baseline, peak esmolol effect, and recovery. Serum esmolol concentrations were obtained to determine the half-life and the elimination rate constant. Esmolol reduced the heart rate, blood pressure, shortening fraction, and cardiac index in all patients, but it did not change systemic vascular resistance. Maintenance esmolol dose was 118 +/- 49 micrograms/kg/min, and the half-life was 2.88 +/- 2.67 min. Blood pressure and heart rate returned to normal within 2-16 min, but cardiac index and shortening fraction took longer to recover. There were no statistically significant age-dependent pharmacodynamic effects, but blood pressure decreased prior to heart rate and cardiac index took longer to recovery in patients who weighed < or = 15 kg. The pharmacokinetic profile in young patients was similar to that of older patients, but the half-life was shorter. The only side effect was transient nausea and vomiting in one patient. Esmolol is a safe and efficacious beta-blocking agent in young patients.

Synthesis, binding properties, and 18F labeling of fluorocarazolol, a high-affinity beta-adrenergic receptor antagonist

New beta-adrenergic receptor antagonists, 2-(R)-(+)- and 2-(S)-(-)-1-(9H-carbazol-4-yl-oxy)-3-[[1-(fluoromethyl)ethyl]amino ]-2-propanol ((S)- and (R)-fluorocarazolols), were labeled with fluorine-18 at the no-carrier-added level by reductive alkylation of desisopropylcarazolol (4-(2-hydroxy-3-amino-1-propoxy)carbazole) with [18F]fluoroacetone. The latter was prepared by nucleophilic substitution of fluoride on acetol tosylate and may serve as a useful synthetic precursor for other radiotracers. The radiochemical yield of [18F]fluorocarazolol (500-1200 Ci/mmol) from [18F]fluoride was 40 +/- 10% at the end of the 45 min synthesis. Chiral HPLC showed > 99% enantiomeric purity of 2-(S)- and 2-(R)-[18F]fluorocarazolols. The log P of fluorocarazolol was 2.2 at pH 7.4. The in vitro KD values of (S)- and (R)-fluorocarazolol for the beta-adrenergic receptor were measured in a rat heart preparation to be KD = 68 and 1128 pM, respectively. Biodistribution experiments in mice demonstrated specific beta-adrenergic receptor binding of (S)-[18F]fluorocarazolol. (R)-[18F]fluorocarazolol showed no observable specific binding to beta-receptors in vivo. The uptake of (R)-[18F]fluorocarazolol may therefore be used as an estimation of nonspecific binding. Positron emission tomography images of pigs showed receptor-specific uptake of (S)-[18F]fluorocarazolol in the heart and lung. Washout of dissociated ligand from the tissue was observed only after 70 min postinjection. The maximum ratio of specific to nonspecific uptake in pig heart and lung was ca. 10 at 150 min postinjection. Observed levels of fluorocarazolol metabolites in mouse and pig blood were relatively low and remained fairly constant during the period from 10 to 180 min postinjection. These results indicate that (S)-(-)-[18F]fluorocarazolol is of interest for use as a radiopharmaceutical for estimation of beta-adrenergic receptors with positron tomography.

Effects of long-term oral carvedilol on the steady-state pharmacokinetics of oral digoxin in patients with mild to moderate hypertension

The effect of multiple oral doses of carvedilol on steady-state plasma digoxin pharmacokinetics was evaluated in 12 patients with mild to moderate hypertension. Area under the curve (AUC), mean maximum plasma concentration (Cmax), mean time to maximum concentration (Tmax), concentration at 24 hours after the dose (C24), creatinine clearance, renal digoxin clearance, and urinary digoxin excretion were determined after patients took oral digoxin 0.25 mg once/day for 2 weeks. Carvedilol was added to the regimen, and digoxin pharmacokinetics were assessed after 2 weeks of concurrent treatment. The AUC and Cmax for digoxin increased by 14% and 32%, respectively (p < 0.05), with no change in Tmax. The 24-hour urinary digoxin excretion and 24-hour renal digoxin clearance increased by 45% and 26%, respectively (p < 0.05), with no change in creatinine clearance. Carvedilol appears to increase digoxin's oral bioavailability as well as renal elimination. The absolute change in digoxin pharmacokinetics was small and not clinically significant. The significance of the interaction in other patient populations remains to be studied.

The affinity of bopindolol and its two metabolites for a beta 2-adrenoceptor in the bovine mesenteric artery

Bopindolol and its two metabolites (18-502 and 20-785) were examined for their affinity to a beta 2-adrenoceptor in the bovine mesenteric artery using the radioligand binding assay method with [3H]CGP12177 as a radioligand. The Scatchard analysis of the data demonstrated a uniphasic plot with Kd and Bmax values of 0.86 +/- 0.16 nM, and 13.34 +/- 1.11 fmol/mg protein, respectively. The pKi values of bopindolol and its two metabolites for beta 2-adrenoceptors in the bovine mesenteric artery were 7.70 +/- 0.13, 8.07 +/- 0.13, 8.20 +/- 0.24, respectively, with 20-785 showing the highest values among these drugs. The present findings indicate that the bovine mesenteric artery membrane is predominantly beta 2-adrenoceptor tissue, and that bopindolol and its two metabolites were potent for beta 2-adrenoceptors in the bovine mesenteric artery.

Beta-adrenoreceptors in the trout (Oncorhynchus mykiss) heart: characterization, quantification, and effects of repeated catecholamine exposure

Specific binding of the hydrophilic radioligand [3H]CGP-12177 to cell surface (functional) beta-adrenoreceptors was quantified in ventricular micropunches (2 mm diameter, 350 microns thickness) from seawater-acclimated rainbow trout held at 7-9 degrees. Binding was stereospecific, saturable, of high affinity, and displaceable by appropriate agonists and antagonists. Phentolamine failed to displace [3H]CGP at concentrations up to 10(-4) M, indicating an absence of [3H]CGP binding to alpha-adrenergic receptors. Trout ventricular beta-adrenoreceptors are exclusively of the beta 2 type. This conclusion is based on (1) the IC50 value for the beta 2-antagonist ICI 118551 (2.9 x 10(-6) M); (2) the inability of the beta 1-antagonist atenolol to displace [3H]CGP from beta-adrenoreceptors; and (3) the order of agonist-binding affinity (isoproterenol > epinephrine >> norepinephrine). The Bmax and Kd values for [3H]CGP binding to myocardial tissue were approximately 0.04 fmol micrograms protein-1 and 0.25 nM, respectively. The Bmax value indicates that the density of cell surface (functional) beta-adreno-receptors in the ventricle was 12,000 sites per cell or 3.38 sites per microns 2 of sarcolemma. The Kd and Bmax values for [3H]CGP binding to ventricular beta-adrenoreceptors were unaffected by the in vivo administration of five bolus catecholamine injections (4.0 micrograms kg-1 epinephrine, 2.0 micrograms kg-1 norepinephrine). This suggests that stress-induced increases in plasma catecholamines are unlikely to cause the down-regulation of heart beta-adrenoreceptors in fish. The method described here represents a simple but powerful technique for the quantification and characterization of adrenergic receptors in the fish heart.

Pharmacokinetics of the enantiomers of tertatolol in the rat after oral and intravenous administration

1. Plasma concentrations of the two enantiomers of tertatolol were determined by gc/ms. Deuterium labelling of one of the tertatolol enantiomers was used for chiral discrimination. 2. No isotope effects were observed following simultaneous oral administration of tertatolol and [2H9]tertatolol. 3. After intravenous administration of the pseudoracemate or of each enantiomer separately, (+)-tertatolol showed a lower total clearance and volume of distribution, compared to the (-) enantiomer. 4. After oral administration of the pseudoracemate or of each enantiomer separately, no substantial difference in bioavailability were observed between the enantiomers.

Esmolol, an ultrashort-acting, selective beta 1-adrenoceptor antagonist: pharmacodynamic and pharmacokinetic properties

The effects of esmolol at different rates of infusion (100, 250 and 500 micrograms.kg-1 BW.min-1) were compared with beta-adrenoceptor occupancy (beta 1 and beta 2, estimated by a subtype selective radioreceptor assay) and plasma concentrations of esmolol and its acid metabolite were measured by HPLC. Up to a rate of infusion of esmolol of 500 micrograms.kg-1 BW.min-1 there was a maximal beta 1-receptor occupancy of 84.7% while beta 2-receptor occupancy was below the detection limit; confirming the beta 1 selectivity of esmolol. Exercise-induced increases in heart rate and systolic blood pressure were reduced by esmolol in a dose-dependent manner. The estimated EC50 values of rate of infusion for the reduction in heart rate and systolic blood pressure during exercise were 113 and 134 micrograms.kg-1 BW.min-1, respectively. Additionally, heart rate and systolic blood pressure were reduced moderately at rest. Because of the short elimination half-life of esmolol caused by the rapid hydrolysis to its acid metabolite, 45 min after end of infusion high plasma concentrations of the metabolite (maximally 80 micrograms.ml-1) but no esmolol were detectable. Since no in vivo effects have been observed, despite the presence of high plasma concentrations of the metabolite, the metabolite did not participate in the observed effects up to an infusion rate of esmolol of 500 micrograms.kg-1 BW.min-1. The plasma concentrations of antagonist detected by radioreceptor assay and plasma concentrations of esmolol detected by HPLC showed a good correlation (r = 0.97).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacokinetics and pharmacodynamics of carvedilol

Carvedilol is an arylethanolamine that is a racemic mixture of 2 enantiomers. The S-(-)-enantiomer has beta-adrenoceptor blocking activity, while the racemate also has alpha 1-receptor blocking activity due to the activity of the R-(+)-enantiomer. The drug is rapidly absorbed and undergoes extensive first-pass metabolism in the liver. It reaches a peak concentration 1 to 2 hours postdose and has an elimination half-life of about 4 to 7 hours. Absorption is delayed by food. The drug is highly lipophilic and is highly protein bound. The drug is metabolised by the liver, with some metabolites having biological activity. The pharmacokinetic profile is not altered in the elderly or in patients with renal disease. However, bioavailability of the oral medication is greatly increased in patients with liver disease. Carvedilol lowers blood pressure as a result of its beta-blocking and vasodilatory activity. The reduction in blood pressure is similar to that achieved with other antihypertensive drugs, and there are no adverse effects on renal or cerebral blood flow. Carvedilol has been used in small numbers of patients with cardiac failure. It reduces left ventricular hypertrophy and has no significant adverse metabolic effects.

Dose-effect and pharmacokinetic-pharmacodynamic relationships of the beta 1-adrenergic receptor blocking properties of various doses of carvedilol in healthy humans

OBJECTIVE

To evaluate the pharmacodynamic properties of carvedilol across a broad range of doses in relation to its enantiospecific kinetics and adrenergic receptor occupancies, relative to placebo and propranolol.

METHODS

Twelve healthy male subjects were investigated on six separate occasions at least 1 week apart when they received either a single peroral dose of 40 mg propranolol, 12.5, 25, 50, or 100 mg carvedilol, or placebo. The subjects were extensively profiled at supine rest, and they underwent supine bicycle ergometry before and at 2, 4, 6, 9, 12, and 22 hours after dosing. At these time points blood was drawn for the high performance liquid chromatographic determination of the enantiomers of carvedilol and for the radioreceptor assay determination of alpha 1- and beta 1-adrenergic receptor binding and related concentrations.

RESULTS

Carvedilol was confirmed to bind to beta 1-adrenergic receptors and (albeit to a lesser extent) to alpha 1-adrenergic receptors. Carvedilol furthermore attenuated the ergometric increase in heart rate in a closely dose-related fashion, which exemplified its beta 1-adrenergic receptor blocking effects. However, the basal efferent adrenergic drive might have been too low to show consistent alpha 1-blocking properties. The radioreceptor and enantiomer kinetics were proportional with dose. There was no indication that the overall kinetic behavior of contributing active metabolites would differ from that of the S(-)-enantiomer. On average, there was a smooth linear relationship between the ergometric treatment responses and log-transformed dose, log-transformed concentrations of the S(-)-enantiomer, and the radioreceptor assay derived beta 1-adrenergic receptor occupancies.

CONCLUSION

The relative complexity of the kinetics of carvedilol (enantiospecific kinetics and dynamics, protein binding, and involvement of active metabolites) does not preclude relatively simple and straight-forward dose-effect and kinetic-dynamic relationships.

Heterologous sensitization of adenylate cyclase activity by serotonin in the rat cerebral cortex

In vitro exposure of rat cerebrocortical slices to microM concentrations of serotonin (5HT) results in an increased response of adenylate cyclase to isoproterenol (ISO). No change in the affinity of the beta-adrenoceptor toward the agonist was found after 5HT exposure when measuring ISO displacement of [3H]CGP 12177 binding. A similar increase of adenylate cyclase response was also found when using VIP as a stimulatory agent. The dose-response curve of adenylate cyclase to the GTP analogue, GppNHp, was modified by 5HT, which promotes a significantly higher maximal response without altering the potency of GppNHp. Forskolin-stimulated adenylate cyclase activity was not affected by 5HT. Serotonergic 5HT2 receptors are involved in the sensitization of adenylate cyclase to GppNHp, since the selective 5HT2 antagonist ketanserin inhibits the effect of 5HT, whereas the 5HT2 agonist DOI mimics 5HT. The involvement of 5HT2 receptor-coupled activation of protein kinase C is also demonstrated: direct protein kinase C activators such as phorbol esters and s,n-dioctanoylglycerol behave in the same manner as 5HT, while the protein kinase C inhibitor CGP 41251 prevents 5HT from increasing adenylate cyclase responsiveness to GppNHp. Moreover, in vitro exposure of cortical slices to 5HT results in reduced inhibition of adenylate cyclase by somatostatin. Since no change was observed at the receptor level and in the direct stimulation of the catalytic subunit of the enzyme, we propose that 5HT might accomplish the sensitization of adenylate cyclase through protein kinase C by inactivating the inhibitory coupling protein Gi and facilitating the interaction of the exogenous GppNHp with the stimulatory coupling protein Gs.

Carvedilol stereopharmacokinetics in rats: affinities to blood constituents and tissues

Carvedilol, a lipophilic beta-adrenoceptor antagonist with vasodilating activities, is characterized by a high as well as stereoselective metabolic clearance and distribution volume. Tissue distribution of carvedilol enantiomers and their conjugates were determined under steady-state conditions in rats (p.o., 10 mg/kg, repetitive dosage; n = 5) and after single i.v. administration in control rats and rats with surgical portacaval shunt (pcs) (10 mg/kg; n = 3 each group). In addition, in vitro plasma protein binding was evaluated. The plasma protein binding of carvedilol in rats is > 98% for total plasma (tp) and > 96% for rat serum albumin (rsa) solution (4%), with enantioselectivity ratios of 1.53 (tp) and 1.27 (rsa). Significantly higher unbound fractions were observed in pcs rats, in part due to reduced protein concentrations. In contrast to plasma, where a preponderance of the R-enantiomer with an S/R ratio of 0.6 was found, S-carvedilol was predominant in all tissues (heart, liver, kidneys, lung, spleen, muscle, and adipose tissue), with S/R ratios of 1.3-1.4 in most of these tissues and 2.3 in liver. This preferential tissue partitioning of S-carvedilol was in accordance with its higher unbound fraction in plasma. Carvedilol accumulated predominantly in the highly perfused and/or eliminating organs liver, kidneys, and lung (tissue/plasma ratios; lung: S 76, R 34; liver: S 21, R 5; kidney: S 8, R 3). A similarly enantioselective distribution into the heart of control as well as pcs rats was observed, where the S-enantiomer concentrations exceeded the plasma concentrations 7-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of the suitability of CGP 12177 for in vivo studies of beta-adrenoceptors

1. Positron emission tomography (PET) with appropriate radioligands offers the possibility of studying receptors non-invasively in man. The suitability of CGP 12177, a hydrophilic non-selective beta-adrenoceptor antagonist which can be labelled with the positron emitter 11C, as a ligand for in vivo studies of beta-adrenoceptors was assessed in rats. 2. [3H]-CGP 12177 was injected into the tail veins of restrained conscious rats. Serial blood samples were taken from tail arteries to determine clearance from plasma. Rats were killed and tissues removed to determine tissue uptake. Radioactivity was assessed by liquid scintillation counting. 3. The uptake of (-)-[3H]-CGP 12177 in various tissues was compared to that of (+/-)-[3H]-CGP 12177. Maximum tissue:plasma ratios obtained for the (-)-enantiomer in lung, heart and liver were 170, 42 and 13 compared with 60, 15 and 12 for the racemate. Prior injection of excess unlabelled (+/-)-CGP 12177 blocked the uptake of both (-)- and (+/-)-[3H]-CGP 12177 in lung and heart but not liver, tissue:plasma ratios for both tracers being reduced to 7, 3 and 7 respectively. 4. Clearance of (-)-[3H]-CGP 12177 from plasma was rapid during the first 5 min but showed only small changes during 5 to 90 min. Uptake in lung and heart reached a maximum at 1 to 5 min and showed a slow decrease during 5-90 min. Prior injection of unlabelled (+/-)-CGP 12177 reduced uptake in lung and heart to 10% and 20% respectively. Injection of unlabelled ( +/-)-CGP 12177 at 15 mind is placed ~75% of the radioactivity by 90 min.5. ( +/- )-Propranolol had a similar effect to that of unlabelled ( +/-)-CGP 12177. Prior injection reduced uptake of radioactivity in lung and heart to 15% and 20% respectively. Injection of ( +/- )-propranolol at 15 min displaced ~ 60% of the radioactivity by 90 min indicating that the tracer binds to beta-adrenoceptor sites in vivo.6. In vivo saturation curves, obtained by injection of (-)-[3H]-CGP 12177 with increasing amounts of unlabelled (- )-CGP 12177, gave values of Bmax for lung of ~45 pmol per g wet weight of tissue and for heart of ~6 pmol per g wet weight of tissue. KD could only be expressed as nmol injected per kg bodyweight, that for lung (2.5 nmol kg-1) being greater than that for heart (1.3 nmol kg-1).7. Competition studies carried out by co-injecting (-)-[3H]-CGP 12177 with unlabelled (+/- )-CGP12177 or (-)-propranolol gave similar values for Bmax (lung 44 pmol g-1, heart 6 pmol g-1,). Values of KD for (+/-)-CGP 12177 (lung 4.7 pmol kg-1, heart 2.6 pmol kg-1) were approximately twice those for(-)-CGP 12177. Values of KD for (-)-propranolol (lung 38 nmol kg-1, heart 104 nmol kg-1) were greater.8. The results show that (-)-[3H]-CGP 12177 is a suitable ligand for assessing beta-adrenoceptors in vivo.

Hemodynamic and pharmacokinetic study of tertatolol in patients with alcoholic cirrhosis and portal hypertension

Tertatolol, a recently developed beta 1-beta 2-blocker has two advantages: it does not induce withdrawal syndrome after abrupt cessation, and it preserves renal function. It has been suggested that the kinetics of tertatolol in patients with hepatic dysfunction are altered. Therefore, the hemodynamic effects and pharmacokinetics following the acute administration of tertatolol were studied in cirrhotic patients with portal hypertension. Systemic, splanchnic and renal hemodynamics were evaluated before and 30 min after the simultaneous administration of 2.5 mg tertatolol p.o. and 1.25 mg deuterated tertatolol i.v. in 10 cirrhotic patients with esophageal varices. The pharmacokinetics of tertatolol were evaluated over a 4-day period. Tertatolol significantly decreased heart rate (-22 +/- 10%), cardiac output (-26 +/- 8%), and hepatic blood flow (-27 +/- 23%). The hepatic venous pressure gradient decreased from 15.7 +/- 5.0 to 12.9 +/- 4.0 mmHg (-17 +/- 13%, P < 0.01). Three out of 10 patients were non-responders to tertatolol. Renal blood flow (-9 +/- 28%) and intrinsic hepatic clearance of indocyanin green (-9 +/- 25%) were not significantly modified. The duration of effective beta-blockade was far less than 12 h. Tertatolol was rapidly absorbed with a Cmax of 70 +/- 51 micrograms/l at a peak time of 0.75 +/- 0.26 h. In comparison with healthy volunteers referred to in literature sources, plasma clearance was reduced to 49 +/- 28 ml/min, bioavailability was increased to 72 +/- 20%, and the volume of distribution was increased to 50 +/- 34 l, probably due, in part, to a weaker protein binding -85%--effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of a pharmacokinetic interaction between carvedilol and digitoxin or phenprocoumon

The possibility of a pharmacokinetic interaction between carvedilol and digitoxin (Study I) or phenprocoumon (Study II) has been evaluated in groups of 12 healthy volunteers. The bioavailability (Cmax, tmax, AUC) of digitoxin and phenprocoumon were assessed after a single dose, given once alone and once on day 6 of treatment with carvedilol 25 mg o.d. Cmax, tmax, AUC and Ut of carvedilol and desmethylcarvedilol were also investigated after the fifth dose of carvedilol and after the sixth dose given concomitantly with digitoxin or phenprocoumon. In Study I, the 95% confidence intervals of the ratio test versus the reference findings were; digitoxin Cmax 0.80-1.20, tmax 0.56-1.14, AUC 0.97-1.33, and for carvedilol Cmax 0.81-1.22; tmax 0.66-1.23; AUC 0.91-1.17. Formation of the active metabolite desmethylcarvedilol and the urinary recovery of carvedilol and desmethylcarvedilol were not influenced by digitoxin. In Study II Cmax and AUC of phenprocoumon were not changed after carvedilol. Cmax of carvedilol was decreased after phenprocoumon. The kinetic parameters of phenprocoumon were Cmax 0.80-1.05, tmax 0.47-2.00, AUC 0.78-1.05, and for carvedilol Cmax 0.59-1.06, tmax 0.71-1.73; AUC 0.80-1.08, respectively. The plasma levels of desmethylcarvedilol and the urinary recovery of carvedilol and desmethylcarvedilol were not influenced by phenprocoumon. The blood pressure and heart rate after carvedilol alone were not affected by concomitant administration of digitoxin or phenprocoumon.

Evidence for an interaction between the beta-blocker pafenolol and bile salts in the intestinal lumen of the rat leading to dose-dependent oral absorption and double peaks in the plasma concentration-time profile

Pafenolol is a beta-blocker with unusual oral absorption properties. The blood concentration-time profile exhibits two peaks, and the bioavailability is low and dose dependent because of incomplete and nonlinear intestinal uptake. We addressed the question whether the intestinal absorption of pafenolol was affected by bile depletion in the gut lumen of rats. Further, the hypothesis that variable gastric emptying accounts for double peaks in blood was tested by duodenal administration of pafenolol. Following intraduodenal administration to rats with intact bile secretion, double peaks were observed in the blood concentration-time curve. The bioavailability was 6.8 +/- 0.7% for the low dose (1 mumol/kg) and increased significantly to 28 +/- 10% following the high duodenal dose (25 mumol/kg). These blood concentration-time profiles exclude interrupted gastric emptying as cause of the twin peaks. In bile duct-cannulated rats the intestinal absorption of the low dose (1 mumol/kg) was still poor (F = 10.7 +/- 5.5%) and the blood concentration-time profile contained two peaks. Following administration of a high duodenal dose (25 mumol/kg) to rats with an almost bile-free small intestine, the absorption rate increased and the double-peak phenomenon disappeared in five of seven rats, while the bioavailability increased significantly, to 62 +/- 27%. These results suggest that the low bioavailability of pafenolol is due to a complexation between bile and pafenolol in the gut lumen, preventing intestinal uptake in the major part of the small intestine. Further, such complex formation in the intestinal lumen may be the underlying mechanism of the double peaks observed in the blood concentration-time profile.

Comparison between carvedilol and captopril in rats with partial ablation-induced chronic renal failure

1. The effect of the novel beta-adrenoceptor antagonist and vasodilator, carvedilol (SK&F 105517, approximately 70 mg kg-1 daily in the food), and captopril (approximately 38 mg kg-1 daily in the drinking fluid) on the progression of chronic renal failure in rats was studied. 2. Six weeks following partial renal ablation, the urinary protein excretion of the carvediol- (60 +/- 21 mg day-1) and captopril-treated (35 +/- 9 mg day-1) animals was less than 50% that of control rats (133 +/- 27 mg d-1). 3. Serum creatinine (Scr) and urea nitrogen (SUN) concentrations of the carvedilol-(Scr, 0.63 +/- 0.09 mg dl-1; SUN, 11.3 +/- 1.2 mg dl-1) and captopril-treated (Scr, 0.82 +/- 0.05 mg dl-1; SUN, 14.1 +/- 1.5 mg dl-1) animals were also significantly (P < 0.05) lower than that observed in control animals (Scr, 1.4 +/- 0.3 mg dl-1; SUN, 19.2 +/- 3.9 mg dl-1), indicating that glomerular filtration rate was improved by both drugs. Plasma renin activity was significantly (P < 0.05) higher in captopril-treated rats (24.7 +/- 4.6 ng angiotensin I ml-1 h-1) than in either carvedilol-treated (7.9 +/- 1.4 ng angiotensin I ml-1 h-1) or control animals (7.4 +/- 1.0 ng angiotensin I ml-1 h-1). 4. Histological examination of the kidneys demonstrated a significantly reduced glomerular hypertrophy and glomerulosclerosis in those animals receiving carvedilol or captopril compared to controls. 5. Serum carvedilol concentration measured every 6 h for 24 h was variable and ranged on average from 57 +/- 13 ng ml-1 at 16 h 00 min to 121 +/- 31 ng ml-1 at 03 h 00 min. These data indicate that the rats probably had 24 h systemic exposure to carvedilol.6. The present study indicates that carvedilol is effective in attenuating the progression of chronic renal failure in rats.

Plasma bevantolol concentration and heart rate in rabbits

Bevantolol (Bev, 5, 10 mg.kg-1) was injected i.v. to rabbits. A measure the lag time of heart rate (HR) response behind the changes in plasma Bev concentration (K(eo)), and the sensitivity of the site of action of Bev (EC50) were determined. The K(eo) were 0.03 +/- 0.02 and 0.029 +/- 0.009 min-1 and the EC50 were 0.2 +/- 0.1 and 0.27 +/- 0.14 microgram.ml-1 respectively for the 2 dosages. The peak changes in HR lagged behind the changes in plasma Bev concentration. There were no significant changes in both pharmacokinetic and pharmacodynamic parameters between the dosages.

Dose-dependent intestinal absorption and significant intestinal excretion (exsorption) of the beta-blocker pafenolol in the rat

The elimination of [3H]pafenolol and metabolites was investigated in fasted and fed rats. Separate groups received intravenous doses (0.3 and 3.0 mumol/kg) and oral doses (1 and 25 mumol/kg). After iv administration of pafenolol, the excretion of unchanged drug into urine and feces was about 50 and 25-30% of the given dose, respectively. The predominating mechanism for the excretion of pafenolol into feces was intestinal excretion (exsorption) directly from blood into gut lumen, since only about 3% of a given iv dose was recovered as pafenolol in the bile. When the oral dose was raised from 1 to 25 mumol/kg, the mean (+/- SD) bioavailability, calculated from urine data, increased from 14 +/- 9 to 30 +/- 11% (P < 0.05) in the starved rats and from 14 +/- 3 to 16 +/- 3% in the fed animals. In parallel, the fraction absorbed from the gut (fa) increased from 19 +/- 9 to 31 +/- 10% in the starved rats and from 16 +/- 4 to 19 +/- 5% in the fed animals, respectively. This indicates that the low bioavailability is due primarily to poor intestinal uptake.

Presystemic elimination of the beta-blocker pafenolol in the rat after oral and intraperitoneal administration and identification of a main metabolite in both rats and humans

Pafenolol is a beta 1-adrenoreceptor antagonist exhibiting some interesting oral absorption properties in both rat and humans. The blood concentration-time profile exhibits two peaks, and the bioavailability is low and dose-dependent due to an incomplete and nonlinear intestinal uptake. The origin of the presystemic metabolism was studied in rats after oral and intraperitoneal administration of tritium-labeled pafenolol with reference to the intravenous route by means of urinary excretion data of pafenolol and metabolites specifically assayed by HPLC and radioisotope detection. The oral-bioavailability increased from 15.8 +/- 4.1% (1.0 mumol/kg) to 33.3 +/- 5.8% (25 mumol/kg, p < 0.001). This was primarily due to a change in the fraction of the absorbed dose (fa) from 21.9 +/- 4.6 to 39.5 +/- 7.9% (p < 0.01). The bioavailability following an intraperitoneal dose was almost complete indicating that the presystemic metabolism was due to gut wall metabolism. Saturation of the presystemic metabolism contributed only by approximately 15-20% to the 2-fold increase of bioavailability. This clearly indicates that the underlying mechanism for the low and dose-dependent bioavailability was an incomplete and nonlinear intestinal uptake. The metabolic pattern showed that at least eight metabolites are formed in the rat. One of these is an alpha-OH pafenolol, identified as the main metabolite in human urine by mass spectrometry.

Saturable enantioselective first-pass effect for carvedilol after high oral racemate doses in rats

Carvedilol shows a highly enantioselective first-pass extraction after therapeutic p.o. doses with preferential extraction of the S-enantiomer. To investigate, whether the enantioselective first-pass metabolism is saturable, male Sprague-Dawley rats were administered increasing single doses of R/S-carvedilol (p.o., 5-30 mg/kg; i.v., 5 and 10 mg/kg), and the individual stereopharmacokinetics were studied. Like in humans the plasma concentrations of R-carvedilol exceeded always those of S-carvedilol. As expected, a dose-dependent reduction in oral clearance was observed, while the total clearance after the i.v. doses was constant. Beyond 20 mg/kg an increased plasma half-life was found for both enantiomers, which is due to a reduced plasma clearance.

Preclinical and clinical pharmacology of carvedilol

Carvedilol is a novel multiple-action cardiovascular drug that has recently been introduced to the market for the treatment of mild to moderate hypertension. Clinical studies have demonstrated that once daily therapy with carvedilol is efficacious and has a favourable side-effect profile. Clinical studies are in progress to establish the utility of carvedilol in angina and congestive heart failure. Carvedilol is a beta-adrenoceptor antagonist and a vasodilator, with the vasodilating activity resulting primarily from alpha 1-adrenoceptor blockade and possibly also from calcium channel blockade. The reduction in BP produced by carvedilol results from the vasodilating activity of the drug because peripheral vascular resistance is significantly reduced. The reduction in BP produced by carvedilol is not associated with reflex tachycardia owing to the beta-adrenoceptor blocking activity of the compound. Throughout its antihypertensive dose range, carvedilol has been a renal-sparing antihypertensive agent in animals and also in humans, inasmuch as renal blood flow, glomerular filtration rate and sodium excretion are all maintained. In preclinical experimental models of acute myocardial infarction, carvedilol has produced marked reductions in infarct size in the pig, rat and dog. The cardioprotection observed with carvedilol is greater than that provided by beta-adrenoceptor antagonists alone, suggesting that the additional activities of carvedilol may provide benefit in the setting of myocardial ischaemia.

Carvedilol. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Carvedilol is a beta-adrenoceptor antagonist which also causes peripheral vasodilation primarily via alpha 1-adrenergic blockade. Carvedilol produces its antihypertensive effect partly by reducing total peripheral resistance by blocking alpha 1-adrenoceptors and by preventing beta-adrenoceptor-mediated compensatory mechanisms. This combined action avoids many of the unwanted effects associated with traditional beta-blocker or vasodilator therapy. In clinical trials published to date, most of which enrolled small numbers of patients, the antihypertensive efficacy of carvedilol administered once daily was similar to that of atenolol, labetalol, pindolol, propranolol, metoprolol, nitrendipine (in elderly patients), slow release nifedipine or captopril in patients with mild-to-moderate essential hypertension. Combined therapy with carvedilol 25 mg and hydrochlorothiazide 25 mg, nicardipine 60 mg or slow release nifedipine 20 mg has an additive antihypertensive effect. Carvedilol and atenolol at similar doses were equally effective at reducing blood pressure in patients who had previously not responded adequately to hydrochlorothiazide monotherapy. As a result of its multiple mechanisms of action, carvedilol is suited for the management of specific groups of hypertensive patients, such as those with renal impairment. In patients with non-insulin-dependent or insulin-dependent diabetes mellitus carvedilol does not appear to affect glucose tolerance or carbohydrate metabolism. Initial studies have demonstrated that carvedilol and slow release nifedipine have similar efficacy in patients with stable angina pectoris and there is evidence that carvedilol has a beneficial haemodynamic effect in patients with congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease. A postmarketing surveillance study has shown that carvedilol is generally well tolerated with only 7% (164/2226) of patients (83% of the total number received 25mg daily for 12 weeks) withdrawing from treatment because of adverse events. Vertigo, headache, bronchospasm, fatigue and skin reactions were the most common events causing withdrawal. Thus, clinical experience to date suggests that carvedilol is likely to be a valuable addition to the options currently available for treating patients with mild-to-moderate essential hypertension, and may offer particular benefit in specific populations of hypertensive patients.

Nipradilol displays a unique pharmacological profile of affinities for the different alpha 1-adrenoceptor subtypes

The selectivity of antagonistic effects of nipradilol, its four isomers and denitronipradilol, a major metabolite of nipradilol, on alpha 1-adrenoceptor subtypes in rat heart, brain and spleen were examined by radioligand binding assay with [3H]-prazosin. Pharmacological characteristics of these compounds were determined in isolated aortae from rats and guinea pigs. The order of the pKi values for alpha 1High-affinity sites in the heart, spleen and brain was SR > nipradiolol > or = RR > or = SS-RS >> denitronipradilol, but the order of the pKi values for the alpha 1Low-affinity sites was different in the heart and brain. There were good correlations between the pKi values of these compounds for the alpha 1High-affinity sites and the pA2 values for the contractile inhibition of the phenylephrine-induced response in rat aorta. There was no correlation between the pKi values of these compounds for the alpha 1Low-affinity sites and the pA2 values. These results indicate that: 1) alpha 1High-Affinity sites are related to vasoconstriction mediated by alpha 1-adrenoceptors; 2) Nipradilol and its isomers possess low affinity to alpha 1-adrenoceptors; and 3) The nitroxy group in nipradilol is important for its alpha 1-blocking activity.

Uptake of radioligands by rat heart and lung in vivo: CGP 12177 does and CGP 26505 does not reflect binding to beta-adrenoceptors

The biodistribution of (-)-4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H-benzimidazol-2-one (CGP12177, a non-selective beta-adrenoceptor antagonist) and 1-[2-(3-carbamoyl-4-hydroxy)-(5-3H-phenoxy)]-2-propanol methanesulfonate, (CGP26505, a beta 1-adrenoceptor antagonist) was studied in rats pretreated with various alpha- and beta-adrenoceptor blocking drugs (5 min before 3H injection, in dosages at which the drugs demonstrated the expected selectivity). Cardiac and pulmonary radioactivity were measured after 10 min, when specific binding was maximal. Uptake of [3H]CGP12177 was linked to binding to beta-adrenoceptors since it was not affected by prazosin or yohimbine, and was equally well inhibited by propranolol, unlabelled CGP12177 and isoprenaline. Moreover, atenolol and CGP20712A inhibited [3H]CGP12177 uptake in heart (predominantly beta 1-adrenoceptors) more potently than ICI 118,551, while in lungs (predominantly beta 2-adrenoceptors) ICI 118,551 was more potent than atenolol or CGP20712A. In contrast, [3H]CGP26505 uptake in the target organs was equally effectively inhibited by propranolol and ICI 118,551, and significantly lowered by alpha-adrenoceptor antagonists. We conclude that [11C]CGP12177, but not [11C]CGP2605 will be suitable for positron emission tomography imaging of beta-adrenoceptors in animals.

Regional gastrointestinal absorption of the beta-blocker pafenolol in the rat and intestinal transit rate determined by movement of 14C-polyethylene glycol (PEG) 4000

The gastrointestinal absorption characteristics of pafenolol following oral administration as a solution in man and rat has previously been found to be a double-peak phenomenon and exhibited dose-dependent bioavailability, despite negligible presystemic metabolism. In both man and rat the first peak appeared approximately 0.5-1 hr postdose and the second, more pronounced peak 3-4 hr postdose. In rat more than 90% of the available dose was absorbed during the second peak. In the present study we investigated the absorption of a solution of pafenolol in rats after intrajejunal and intraileal administration. The resulting blood concentration-time profile of pafenolol exhibited one peak only; the extent of absorption was similar to that observed when the same dose was given orally. The small intestinal transit time of the 14C-PEG 4000 solution was found to be more than 3 hr. The transit rate was higher in the proximal part of the small intestine compared to the more distal part, where the transit of the solution was staggered. In conclusion, the results of the intestinal transit time investigation and the administrations of pafenolol at different levels of the alimentary tract indicate that pafenolol is a drug with a specific absorption site located in the ileocolonic region.

Rats with portacaval shunt as a potential experimental pharmacokinetic model for liver cirrhosis: application to carvedilol stereopharmacokinetics

As an experimental model for reduced liver function rats with surgical portacaval shunts (pcs) may be used. Carvedilol, a nonselective beta-adrenoceptor antagonist with vasodilating activity, is extensively metabolised by phase I as well as phase II pathways. In order to study the stereoselective pharmacokinetics of carvedilol in liver disease, pcs and control rats were given rac-carvedilol intravenously and p.o. The carvedilol enantiomers and their conjugates were assayed in plasma, urine, and bile. Carvedilol was highly bound to plasma proteins; binding was reduced by pcs. In all groups, the plasma concentrations of (R)-carvedilol exceeded those of (S)-carvedilol significantly. In comparison to the control group the plasma concentrations of both enantiomers increased after pcs, while the difference between the stereoisomers decreased. The total clearance decreased proportionally to the decrease in liver weight (30%). Both the apparent oral clearance, as well as its stereoselectivity were reduced, by up to 90 and 43%, respectively. The biliary clearance of the parent drug after i.v. dosage increased in rats with pcs due to the reduced hepatic metabolism.

Suitability of CGP-12177 and CGP-26505 for quantitative imaging of beta-adrenoceptors

[3H]CGP-12177, a non-selective beta-adrenoceptor antagonist, and [3H]CGP-26505, a beta 1-selective beta-adrenoceptor antagonist, were intravenously administered to rats. 94-97% of the injected radioactivity disappeared from plasma with t1/2 0.2 and 0.5 min. Total/non-specific binding ratios of 5.4 and 6.9 (CGP-12177) or 2.0 and 2.8 (CGP-26505) were maintained in heart and lung from 10 to 40 min post-injection. Labelled plasma metabolites appeared after greater than 20 min (CGP-12177) or within 2 min (CGP-26505). No metabolites were found in the heart. CGP-12177 binds to blood cells, but CGP-26505 does not. CGP-12177 can be used for PET imaging of total (beta 1 and beta 2) adrenoceptors in the heart and lung of experimental animals, but CGP-26505 is less suitable for in vivo analysis of the beta 1-subpopulation.

Preparation and in vivo binding of [11C]carazolol, a radiotracer for the beta-adrenergic receptor

Carazolol is a high affinity beta-adrenergic receptor antagonist which is relatively non-specific for the receptor subtypes. The labeling of the two enantiomers of this compound with carbon-11, including the synthesis of the required labeling precursors, is reported. The yield and specific activity are sufficient for use in positron tomography. Biodistribution and specific receptor binding studies show the labeled material to be of interest for further investigation as a radiopharmaceutical for positron tomography.

Electropharmacologic effects and pharmacokinetics of almokalant, a new class III antiarrhythmic, in patients with healed or healing myocardial infarcts and complex ventricular arrhythmias

The electropharmacologic effects and pharmacokinetics of almokalant, a new class III antiarrhythmic, were investigated in a randomized, placebo-controlled, double-blind study, and efficacy was evaluated. Ten post-myocardial infarction patients with complex ventricular arrhythmias were included and received, in randomized order on consecutive days, 4.5 mg (12.8 mumol) of almokalant or placebo intravenously over 10 minutes. One patient received infusion at a higher rate and developed self-terminating torsades de pointes. In the remaining 9 patients the corrected QT interval increased significantly: At the end of placebo infusion the corrected QT was 445 +/- 18 ms and after almokalant 548 +/- 53 ms (p = 0.0015). The signal-averaged electrocardiographic parameters did not change. The number of ventricular premature complexes decreased significantly during the first 15 minutes after almokalant infusion (p = 0.04). No additional proarrhythmic or other significant adverse events were noted. The almokalant plasma concentration showed a biphasic decrease with an elimination half-life of 2.4 +/- 0.1 hours. Almokalant was rapidly cleared from the body with a clearance of 11 +/- 1 ml/min/kg. When given with certain precautions almokalant appears safe and well-tolerated and may be antiarrhythmic by prolonging refractoriness.

Interaction of talinolol and sulfasalazine in the human gastrointestinal tract

The absorption of talinolol (TA) 50 mg was investigated without and together with the co-administration of sulfasalazine (SASP) 4 g in 11 healthy young volunteers, in order to clarify gastrointestinal transit of TA. Without SASP, the tmax of TA was 2.8 h, Cmax was 112 ng.ml-1 and the half life was 12 h; the AUCo-t was 958 ng.ml-1.h. In the case of concomitant administration of SASP, TA was found only in serum from 3 individuals, with a Cmax of 23 ng.ml-1 and a mean AUCo-t of 84 ng.ml-1.h. TA was not detectable in 5 subjects and it was at the limit of detection (2 ng.ml-1) in 3 subjects. Pharmacokinetic analysis was not possible in any of those individuals. The reason for the interaction appears to be the adsorption of TA by SASP. An interval of 2-3 h should elapse between giving SASP and other drugs.

Measurement of sarcolemmal vesicle orientation by beta-adrenergic receptor binding

To assess the orientation (inside-out vs. outside-out) of purified cardiac sarcolemmal vesicles, we developed a new method utilizing the known outward-facing binding site of the beta-adrenergic receptor. We compared the binding of the lipid-insoluble ligand 3H-CGP-12177, which binds to beta-adrenergic receptors on outside-out sarcolemmal vesicles only, to the binding of the lipid soluble ligand 125I-iodocyanopindolol, which binds to beta-adrenergic receptors in sarcolemmal vesicles of either orientation. The ratio of CGP to ICYP binding is equal to the fraction of outside-out sarcolemmal vesicles. Sidedness measurements by beta-adrenergic receptor-binding showed similar mean values but less scatter than sidedness assessments by measurement of 3H-ouabain-binding or Na+,K(+)-ATPase activity in the presence or absence of membrane permeabilizing agents.

Therapeutic effects of arotinolol, a beta-adrenergic blocker, on tremor in MPTP-induced parkinsonian monkeys

The effect of arotinolol, a peripherally acting beta-adrenergic-blocking agent, on postural or kinetic tremor was studied in monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism. Male cynomolgus monkeys (Macaca fascicularis) were treated with three injections of MPTP hydrochloride (0.3 mg/kg, i.v.) at an interval of 3-4 days, followed by several injections of the same dose every 7 days. Four monkeys with persistent parkinsonian symptoms manifested for greater than 1 year were used. The animals developed mild to moderate degrees of postural or kinetic tremor, and their motor activity was reduced. Arotinolol (20-30 mg/kg, s.c.) significantly suppressed postural tremor in a dose-dependent manner. Propranolol (20-30 mg/kg) was also effective in suppressing the tremor. However, the application of propranolol induced emesis, whereas arotinolol had no adverse effects. These results suggest that arotinolol is a useful adjunct to dopaminergic therapy for tremor in Parkinson's disease.

Effects of Acute Febrile Infectious Diseases on the Oral Pharmacokinetics and Effects of Nitrendipine Enantiomers and of Bisoprolol

In 2 longitudinal studies with 10 patients each, the stereoselective pharmacokinetics of nitrendipine and the pharmacokinetics of racemic (rac) bisoprolol (both 20mg orally) were investigated during acute febrile infectious diseases and at least 6 weeks later in the healthy state. The area under the plasma concentration-time curve (AUC) and peak plasma concentration (Cmax) of rac-nitrendipine were increased in the infectious state by 89% [95% confidence interval (CI): 24 to 187%] and 95% (95% CI: 22 to 209%), respectively. Similar increases were observed for both S- and R-nitrendipine. Nitrendipine exhibited stereoselective pharmacokinetics in both the healthy state and the infectious state, but the mean ratios of S:R AUC values [healthy: 1.79 (95% CI: 1.36 to 2.11); infectious: 1.87 (95% CI: 1.62 to 2.11)] were not different. The elimination half-life, protein binding and haemodynamic effects of nitrendipine also did not differ between the infectious and the healthy state. The mechanism for the disease effects may be related to suppression of hepatic cytochrome P450 activity by mediators of inflammatory reactions. On the other hand, none of the pharmacokinetic parameters, including nonrenal clearance, of rac-bisoprolol was changed during febrile infectious disease, indicating specificity in the effects of acute febrile disease on oxidative drug metabolism.

Pharmacokinetic and blood pressure effects of carvedilol in patients with chronic renal failure

The pharmacokinetic and acute systemic haemodynamic effects of a single oral dose of 50 mg carvedilol has been studied in 24 hypertensive patients with chronic renal failure. The patients were stratified into 3 groups according to the creatinine clearance: I 51-90 ml.min-1; II 26-50 ml.min-1; III 4-25 ml.min-1. The area under plasma level time curve AUC, the elimination half-life t1/2, the maximum plasma concentration Cmax, the time to peak concentration tmax were not significantly different between groups, whereas the amount of unchanged drug or metabolite excreted in urine Ae and the renal clearance CLR of carvedilol and its metabolites M2, M4, M5 were significantly decreased in Group III. Blood pressure and heart rate decreased in all 3 groups of patients after acute administration of 50 mg carvedilol. Mild adverse effects were reported in 6 patients. Despite a decrease in the renal clearance of carvedilol and of its metabolites with decreasing kidney function, its main pharmacokinetic parameters remained unchanged. The present results suggest that the dose of carvedilol need not be reduced in hypertensive patients with chronic renal failure.

[Esmolol--beta-adrenergic blocking agent with ultrashort action]

Esmolol is a new, highly efficient, cardioselective beta-adrenergic receptor blocking agent for intravenous use only. Its action commences rapidly and its duration is very short (about 15 min). It is very quickly metabolized in the body into an inactive product, and hence its therapeutic effect can be easily controlled. Indications for its use are supraventricular tachyarrhythmias and hypertension during the perioperative period and noncompensated sinus tachycardia. Esmolol is considered as drug of choice in its indicational domain and hence it is being introduced into materia medica in the increasing number of countries. Its therapeutic range is wide. Hypotension is the most frequent side effect of esmolol, while bradycardia, congestive heart failure, hypotension and cardiogenic shock are the most important contraindications for its use.

High‐Performance Liquid Chromatographic Method for Determination of Ronactolol in Urine and Plasma: Evaluation of Pharmacokinetic Parameters in Healthy Humans

Ronactolol [(+/-)-4'-[2-hydroxy-3-(isopropylamino)propoxy]-p-anisanilide], a new aminopropanol derivative showing beta-adrenoreceptor blocking activity, was administered orally as capsules to healthy humans at three single doses (30, 60, and 120 mg). Two HPLC methods were developed separately for determination of drug levels in urine and plasma. For plasma samples, after addition of internal standard (IS), a single-step extraction of alkalinized plasma was performed with methylene chloride. The organic layer was evaporated to dryness under reduced pressure, and the residue was taken up and chromatographed on a microbore silica column. Ronactolol and IS were detected by a UV detector at a wavelength of 278 nm. Excellent linearity was observed between the peak height ratios (ronactolol:IS) and concentrations in plasma. The lowest limit of detection (signal:noise, 3:1) was 1.5 ng/mL of plasma. Urine samples were directly injected and chromatographed on a microbore C18 column with an ion-pairing mobile phase. Excellent linearity was observed between the peak areas and concentrations in urine. The lowest limit of detection (signal:noise, 3:1) was 75 ng/mL of urine. The assay was used to determine the main pharmacokinetic parameters in healthy humans.

Short-acting beta-adrenergic blockade and the fetus. A case report

An infant was born to a woman who received intravenous esmolol for intrapartum supraventricular tachyarrhythmia. Despite the very short acting and cardio-selective beta-1 adrenergic blockade induced by that agent, neonatal effects can occur up to 48 hours after delivery.

Oral administration of carvedilol and prazosin inhibits the prostaglandin F2 alpha- and noradrenaline-induced contraction of human hand veins in vivo

Carvedilol is a beta-blocker with additional vasodilating activity. This study was performed in order to determine whether the vasodilator action of orally administered carvedilol in man is based upon an alpha-adrenoceptor antagonism exclusively or if evidence for an additional mechanism could be confirmed. The influence of carvedilol (50 mg p.o.) and prazosin (2 mg p.o.) upon the vasoconstrictor effect of noradrenaline and prostaglandin F2 alpha, infused into superficial hand veins, was established in 8 healthy male volunteers. Increasing dosages of the vasoconstrictors below their threshold of systemic activity were employed in order to obtain dose-response curves of the hand veins congested at a venous occlusion pressure of 40 mmHg. These dose-response curves were repeated 1 and 3.5 h after oral administration of either carvedilol, prazosin, or placebo. The ex vivo, in vitro alpha 1-receptor occupancy in plasma was measured before and after each vasoconstrictor dose-response curve, using an alpha 1-radioreceptor binding assay. Washout periods of 48 h were kept between study days, investigating the influence of one orally administered drug upon one of the local vasoconstrictor dose-response curves at a time. In the alpha 1-radioreceptor assay, plasma concentrations from 0.9- to 1.7-fold the equilibrium dissociation constant (Ki) of carvedilol could be evaluated 1 as well as 3.5 h after medication, corresponding with a receptor occupancy of 44%-63%. After prazosin, 9-13 times the Ki values were determined, which amounts to an alpha 1-adrenoceptor occupation of about 90%-93%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of carvedilol on adrenergic receptor pharmacology in human ventricular myocardium and lymphocytes

Carvedilol, a new beta-blocker with vasodilating properties due to alpha 1-blockade, was investigated in preparations of human ventricular myocardium. Carvedilol demonstrated a high affinity and is a slightly beta 1-selective competitive beta-blocking agent, with a KD for beta 1-receptors of approximately 4-5 nM and a mild selectivity for beta 1 vs. beta 2 receptors of 6- to 39-fold, depending on the method employed to assess subtype potency. In addition, carvedilol was also a potent alpha 1-blocking agent, with a beta 1:alpha 1 blocking relative potency of 1.7-fold. In human lymphocytes containing beta 2-receptors and in human myocardial membranes containing both beta 1- and beta 2-receptors carvedilol exhibited the unique property of guanine nucleotide modulatable binding. Despite this, no intrinsic sympathomimetic activity of carvedilol was detected in preparations of isolated human heart or in myocardial membranes. Vasodilation related to alpha 1-blockade and the lack of intrinsic activity should translate into improved tolerability and good efficacy in the treatment of heart failure.

Clinical experience with dual-acting drugs in hypertension

There are now several antihypertensive agents with dual actions. Among these, labetalol has been studied most extensively. The drug has a place in the chronic treatment of hypertension and in the therapy of hypertensive emergencies. Carvedilol, now available in Germany, has been shown to be effective in different forms of hypertension. Celiprolol binds to beta 1- and beta 2-receptors. This drug also binds to alpha 2-receptors. It is not clear, at present, whether or not this binding property contributes to its antihypertensive effect.

Pharmacokinetics and efficacy of carvedilol in hypertensive patients with chronic renal failure and hemodialysis patients

The efficacy, safety, and pharmacokinetics of carvedilol were investigated in an open trial performed on 13 hypertensive patients with chronic renal failure and six additional patients requiring hemodialysis. In hypertensive renal failure patients, treatment with carvedilol (5 mg/day) for 1 week produced a significant decrease in blood pressure (from 172/101 to 146/84 mm Hg) but did not change the heart rate. The pharmacokinetics of carvedilol did not change with repeated administration, and there was no accumulation of this drug. In hemodialysis patients with hypertension, the pharmacokinetics of carvedilol after a single dose of 10 mg did not vary between dialysis and nondialysis days, and blood pressure decreased significantly on both days. In addition, there was no accumulation of carvedilol during a 4-week trial of therapy, and blood pressure was decreased significantly from 170/93 to 145/83 mm Hg. There were no side effects and no abnormal laboratory findings noted during the trial. These results indicate that carvedilol is an effective and safe agent for hypertensive patients with chronic renal failure and for hemodialysis patients with hypertension and that dosage adjustments are probably not required in these clinical situations.

Disposition of carvedilol enantiomers in patients with liver cirrhosis: evidence for disappearance of stereoselective first-pass extraction

The racemic drug carvedilol exerts its antihypertensive action through vasodilation and nonselective beta-blockade. The R(+)-enantiomer has twice (31.1%) the absolute bioavailability than the S(-) form (15.1%). The pharmacokinetics of the enantiomers were investigated after intravenous (i.v.) (12.5 mg in 1 h) and p.o. (25 mg) administration of racemic carvedilol in six patients with cirrhosis of the liver according to a randomized crossover design. Although the difference between areas under the curve of R(+) and S(-) were of borderline significance after i.v. administration but significant after oral administration, no difference existed between the absolute bioavailabilities of R(+) (83.7%) and S(-) (71.3%). The enantiomer ratio is similar after i.v. (1.3) and p.o. administration (1.6). In contrast to healthy subjects, the apparent volume of distribution of S(-) is about 90% greater than that of R(+) in patients. The renal excretion of carvedilol and of one of its major metabolites, carvedilol glucuronide, also exhibited stereoselective behavior, but in opposite directions. In patients with liver cirrhosis, stereoselective metabolism of carvedilol is still operative. However, probably because of portocaval shunts, the hepatic first-pass extraction is markedly reduced, eliminating the difference in bioavailability between the two enantiomers.

Stereoselective disposition and tissue distribution of carvedilol enantiomers in rats

After intravenous bolus injection of rac-carvedilol at 2 mg/kg to the rat, the (+)-(R)- and (-)-(S)-enantiomer levels in the blood and tissues (liver, kidney, heart, muscle, spleen, and aorta) were measured by stereospecific HPLC assay. As compared with the (+)-(R), the (-)-(S) had a larger Vdss (3.32 vs. 2.21 liter/kg), MRT (33.4 vs. 25.6 min), and CLtot (96.1 vs. 83.8 ml/min/kg). AUC comparison after iv and po administration showed systemic bioavailability of the (-)-(S) to be about half that of its antipode, explained by the fact that the free fraction of the (-)-(S) in blood was 1.65-fold greater than that of the (+)-(R). Tissue-to-blood partition coefficient values for the (-)-(S) were 1.6- to 2.1-fold greater than those for the (+)-(R) in all tissues, showing that the (-)-(S) accumulates more extensively in the tissues. These results were consistent with the greater Vdss for the (-)-(S) estimated from systemic blood data. The stereoselective tissue distribution of carvedilol enantiomers results from an enantiomeric difference in plasma protein binding rather than in tissue binding.

Metabolism of carvedilol in man

The metabolism of carvedilol was investigated in plasma and urine of 3 healthy male volunteers after administration of 50 mg of [14C]-labelled drug. Rapid and extensive biotransformation occurred. After 1.5 h 9% of total radioactivity in plasma consisted of unchanged drug, 22% of carvedilol-glucuronide and another 20% of oxidative cleavage products of the beta-blocking side chain. Urinary excretion of radioactivity amounted to 16% of which 2% represented unchanged drug, 32% carvedilol-glucuronide and about 25% side chain oxidation products. Ring-hydroxylated metabolites of carvedilol accounted for 18% of the radioactive compounds in the urine.

[The covalent binding of a potent beta-receptor blocker (B 24/76) on tissue proteins and collagen in the rat]

Toxic effects of drugs and their metabolism may be caused by covalent binding to cellular macromolecules. After oral application of the tritiated beta-blocker B 24/76 to male Wistar rats only the liver showed a significant irreversible binding to tissue proteins, with 11% of the radioactivity distributed in this organ. A covalent binding to collagen was found in liver, lung and muscle. The highest part was measured in the lung with 7% of the radioactivity distributed in this organ.