Controlled beta-receptor blockade with esmolol and flestolol

β-Adrenergic blockade in cardiovascular disease

The development and subsequent clinical application of the β-adrenergic receptor blocking drugs represent one of the major advances in human pharmacotherapeutics. No other class of synthetic drugs has demonstrated such widespread therapeutic utility for the treatment and prevention of so many cardiovascular diseases. In addition, these drugs have proven to be molecular probes that have contributed to our understanding of the disease, and on the molecular level, both the structure and function of the 7 transmembrane G protein receptors that mediate the actions of many different hormones, neurotransmitters, and drugs. The evolution of β-blocker drug development has led to refinements in their pharmacodynamic actions that include agents with relative β1-selectivity, partial agonist activity, concomitant α-adrenergic blockers activity, and direct vasodilator activity. In addition, long-acting and ultra-short-acting formulations of β-blockers have also demonstrated a remarkable record of clinical safety in patients of all ages.

The negative inotropic effect of esmolol on isolated cardiac muscle

OBJECTIVE

Esmolol is an ultra-short-term acting beta adrenergic blocker for intravenous use. The most common side effect is hypotension, which is often manageable by careful titration of the dose. We speculated whether esmolol had a direct negative inotropic effect on the cardiac muscle.

DESIGN

Papillary muscles and trabeculae were excised from guinea pig and pig hearts. Force production was recorded together with action potentials. Membrane currents were recorded in isolated myocytes. The effects of two concentrations of esmolol were tested (55 and 110 micromol/L).

RESULTS

Esmolol reduced action potential duration and plateau voltage, and decreased force production of isolated cardiac muscle. Voltage-clamp experiments from a holding potential of -40 mV and a step change to 0 mV showed a reduction in the inward current due to esmolol.

CONCLUSION

Apart from being a beta adrenergic blocker esmolol also exerts a direct negative inotropic effect on cardiac muscle due to its inhibition of the calcium current during the action potential.

Beta-adrenergic blockers in systemic hypertension: pharmacokinetic considerations related to the current guidelines

Beta-adrenergic blockade has provided one of the major pharmacotherapeutic advances of the 20th century. Beta-blockers are first-line drugs for the management of systemic hypertension, used alone and in combination with other antihypertensive agents. Drugs in the beta-blocking class have the common property of blocking the binding of catecholamines to beta-adrenergic receptor sites; however, there are significant pharmacodynamic and pharmacokinetic differences between the individual agents that are of clinical importance. Among these differences are the completeness of gastrointestinal absorption, the degree of hepatic first-pass metabolism, lipid solubility, protein binding, brain penetration, concentration within the cardiac tissue, rate of hepatic biotransformation, and renal clearance of drug and/or metabolites. Long-acting formulations of existing beta-blockers are currently in use, and ultra-short-acting agents are also available. Age, race, cigarette smoking and concomitant drug therapy can also influence the pharmacokinetics of beta-blocking drugs. The wide interpatient variability in plasma drug concentrations observed with beta-blockers makes this parameter unreliable in routine patient management. Despite the pharmacokinetic differences among beta-blockers, these drugs should always be titrated to achieve the desired individual patient response.

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE

We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations.

METHODS

Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured.

RESULTS

Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury.

CONCLUSIONS

Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.

Evaluating a possible pharmacokinetic interaction between remifentanil and esmolol in the rat

Remifentanil (Ultiva) is a novel, ultra-short-acting opioid which has recently been approved for use as an analgesic during induction and maintenance of general anesthesia. Esmolol is a short-acting beta-blocker used during surgical procedures to reduce heart rate and blood pressure. Both drugs are metabolized by nonspecific esterases in the blood and other tissues and may be administered concomitantly during surgery. The goal of this study was to determine if coadministration of esmolol significantly alters the pharmacokinetics of remifentanil in the rat. Two groups of rats were dosed with remifentanil [25 micrograms/kg/min (n = 8)] and remifentanil plus esmolol [25 and 200 mg/kg/min (n = 7)] for 20 min. Cardiovascular measurements were collected continuously over the course of the study. Serial blood samples (12) were collected over 25 min into test tubes containing 0.5 mL of acetonitrile. Blood samples were extracted (liquid-liquid) with methylene chloride and then analyzed by a validated GC-MS assay. Compartmental data analysis was performed using PCNONLIN. The mean(+/- SD) for Cl and t1/2 observed in treatment I were 390(+/- 98) mL/min/kg and 0.69(+/- 0.27) min and in treatment II were 421(+/- 164) mL/min/kg and 0.56(+/- 0.22) min, respectively. Comparison of clearance, volume of distribution, and terminal half-life between the two groups showed that coadministration of esmolol had no significant (p < 0.05) effect on the pharmacokinetics of remifentanil in the rat.

Soft drugs. XX. Design, synthesis, and evaluation of ultra-short acting beta-blockers

A new type of ultra-short acting beta-blocker which might prove advantageous in treating acute arrhythmias was designed, synthesized and investigated. Based on the soft drug "inactive metabolite approach," the inactive phenylacetic acid metabolite of both metoprolol and atenolol was reactivated by esterification with sulfur-containing aliphatic alcohols. Since the sulfur-containing moieties are labile to the ubiquitous esterases, the new compounds should be inactivated by a one step enzymatic cleavage back to the inactive phenylacetic acid derivative. Pharmacological and pharmacokinetic profiles of the new compounds were evaluated in rats and rabbits. Isoproterenol-induced tachycardia was inhibited with short-term infusion of each compound. This tachycardia blocking effect rapidly disappeared upon termination of infusion, while beta-blocking activity was 2-4-fold longer after comparable doses of the short-acting beta-blocker, esmolol. The rapid recovery from the beta-receptor blockade is believed due to fast hydrolysis of the soft drugs in the body. This is supported from in vitro results showing the t1/2 of esmolol is about 10-fold longer than the new soft drugs in rat, rabbit, dog and human blood. Hydrolysis studies in phosphate buffered solutions indicated that the esters are labile to base-catalyzed hydrolysis. However, the relative t1/2 values measured in biological media compared to phosphate buffered solution clearly support rapid enzymatic cleavage of the soft drugs. Interestingly, one of the soft beta-blockers, the sulfonyl ester derivative, showed a unique property of exhibiting good beta-receptor blocking activity without significant hypotensive action.

A new dosing regimen for esmolol to treat supraventricular tachyarrhythmia in Chinese patients

OBJECTIVES

The purpose of this study was to find a safe dosing regimen for esmolol infusion to rapidly control supraventricular tachyarrhythmia after cardiac surgery in Chinese patients.

BACKGROUND

Tachycardia increases cardiac work but reduces myocardial perfusion. Thus, in the critical period immediately after cardiac surgery, tachycardia itself warrants urgent intervention. Esmolol, an ultrashort-acting beta-adrenergic blocking agent, has been reported in western published reports to have good results and few side effects in the treatment of supraventricular tachyarrhythmia. However, its clinical application in Chinese patients has not yet been reported.

METHODS

When supraventricular tachyarrhythmia with a rapid ventricular response (> 110/min) was found early after cardiac surgery, esmolol infusion with a different dosing regimen was used to control the tachyarrhythmia.

RESULTS

With the dosing regimen recommended in western published reports (repeated loading infusion with stepwise increment), acute hypotension with systolic pressure < 80 mm Hg occurred in all six patients after 1 min of loading infusion of esmolol (500 micrograms/kg body weight per min). To avoid the aforementioned complications, a new dosing regimen was constructed. The initial infusion rate of esmolol was set at 150 or 100 micrograms/kg per min, depending on the patient's age and blood pressure. When the desired heart rate was achieved, the initial infusion rate was reduced to the maintenance infusion rate to maintain the therapeutic effect [Maintenance infusion rate = Initial infusion rate x (1 - e-0.077t), where t is the time period in minutes required by the initial infusion of esmolol to achieve the therapeutic effect]. With this new dosing regimen, tachycardia in most patients (9 of 11) could be controlled within 10 min, and no one experienced the side effect of hypotension. The maintenance infusion rate of esmolol needed to control supraventricular tachyarrhythmia in our patients was only 73 +/- 42 micrograms/kg per min (mean +/- SD), much less than that noted in western reports.

CONCLUSIONS

The dosing regimen for esmolol infusion recommended in western studies is not suitable for Chinese patients. In this report we propose a new dosing regimen for esmolol infusion that is both safe and rapid in the treatment of supraventricular tachyarrhythmia in Chinese patients.

Advances in cardiovascular pharmacological therapy

Progress in the pharmacological management of cardiovascular disease has been accompanied by the appearance of drugs with never before seen capabilities to alter human physiological processes. The widespread use of these potent agents poses a challenge to the oral and maxillofacial surgeon attempting to safely manage patients in the ambulatory setting. This article reviews the field of contemporary cardiovascular pharmacotherapy from the aspect of how it affects the practice of oral and maxillofacial surgery.

Bolus administration of esmolol for controlling the haemodynamic response to tracheal intubation: the Canadian Multicentre Trial

A multicentre trial was designed to determine the dose-response and side-effects of esmolol when administered as a single iv bolus prior to induction of anaesthesia for controlling the haemodynamic response to tracheal intubation. Five hundred and forty-eight patients from 12 university-affiliated centres across Canada were randomized prospectively to receive either placebo (PLAC) or esmolol (E) in a dose of 100 mg (E100) or 200 mg (E200). Study medication was given immediately before induction of anaesthesia with thiopentone 3-5 mg.kg-1 and succinylcholine 1.5 mg.kg-1. Low-dose narcotic (fentanyl 2-3 micrograms.kg-1 or sufentanil 0.3 micrograms.kg-1) or moderate dose narcotic (fentanyl 4-7 micrograms.kg-1) was also given at five of the participating centres, whereas patients in the remaining seven centres received no narcotic. Patients who received PLAC and no narcotic had greater HR and SBP values after tracheal intubation than patients who received either E100 or E200 (P less than 0.005). The proportion of patients whose maximum HR exceeded 110 min-1 was also greater in the PLAC group (22/180) than in either the E100 (10/187) or E200 (9/181) groups (P less than 0.05), but was not different when comparing E100 with E200. Esmolol was less effective in controlling blood pressure, but, in combination with low-dose narcotic, esmolol suppressed the SBP response to tracheal intubation. In the presence of moderate-dose narcotic, however, a decrease in SBP occurred in all three groups following induction of anaesthesia (P less than 0.003), with the largest decrease (17 +/- 4%) occurring in patients who had received E200. The overall incidence of hypotension (SBP less than 90 mmHg) was greater in the E200 group (33%) than either the E100 (25%) or PLAC (16%) groups (P less than 0.05). Other side-effects, such as bradycardia, bronchospasm or pain on injection, occurred no more frequently in either esmolol group than with placebo. It is concluded that a 100 mg bolus of esmolol is safe and effective for controlling the haemodynamic response to tracheal intubation. This dose of esmolol combined with a low dose of narcotic (fentanyl 2-3 micrograms.kg-1 or equivalent) results in effective control of both heart rate and blood pressure, while avoiding important side-effects.