Ultra-short-acting beta-adrenergic blockers

ART─An Amino Radical Transfer Strategy for C(sp2)-C(sp3) Coupling Reactions, Enabled by Dual Photo/Nickel Catalysis

Introducing the novel concept of amino radical transfer (ART) enables the use of easily accessible and commercially available alkyl boronic esters as cross-coupling partners for aryl halides in dual photoredox/nickel catalysis mediated by visible light. Activation of otherwise photochemically innocent boronic esters by radicals generated from primary or secondary alkylamines gives rise to an outstanding functional group tolerance in a mild, fast, and air-stable reaction. As shown in more than 50 examples including unprotected alcohols, amines, and carboxylic acids, this reaction allows quick access to relevant scaffolds for organic synthesis and medicinal chemistry. In comparison with existing methods for C(sp²)-C(sp³) couplings an extraordinary generality could be realized via the ART concept, employing a single set of optimized reaction conditions. Due to its selectivity, the transformation can also be used for late-stage functionalization, as demonstrated with three exemplary syntheses of drug molecules. Furthermore, the successful one-to-one scalability of this reaction up to gram scale without the necessity of any further precautions or flow systems is demonstrated.

Comprehensive management of hypertensive emergencies and urgencies

Despite advances in chronic hypertension management, hypertensive emergencies and urgencies remain as serious complications. Much of this relates to poor compliance with effective antihypertensive management. Hypertensive emergencies and urgencies can also be seen as the initial manifestations of hypertension in pregnancy and in the perioperative period. Multiple classes of intravenous antihypertensive drugs are available to treat hypertensive emergencies, and specific agents may have an advantage in a given clinical situation. Orally active agents are used to treat hypertensive urgencies, and include clonidine, angiotensin-converting enzyme inhibitors, and labetalol. Most patients respond to drug therapy, but problems may arise related to a rapid normalization of blood pressure.

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.

The lack of effect of aerobic exercise training on propranolol pharmacokinetics in young and elderly adults

The effects of exercise training on the pharmacokinetics of orally administered propranolol were studied in young and elderly healthy volunteers. Twenty-three young (30 +/- 5 years of age) and 20 elderly (67 +/- 5 years of age) adults were randomly assigned to endurance training (N = 12 young subjects, 10 elderly subjects) or nonexercising control (N = 11 young subjects, 10 elderly subjects) groups. Training consisted of treadmill walking, stair climbing, or both three times per week for 40 minutes at 70-85% of maximal heart rate reserve for 16 weeks. Resting plasma propranolol concentrations after a single dose of 80 mg of oral propranolol were measured by high performance liquid chromatography with fluorescence detection, and estimated hepatic blood flow measured was measured using indocyanine green during supine test. Aerobic training increased maximal oxygen uptake (VO2 max) by 13% and 14% in the exercising young and elderly groups, respectively. There was no change in VO2 max in either control group. Adjusted mean estimated hepatic blood flow after exercise corrected for body weight for the young subjects who did not exercise (15.6 mL/min/Kg) and those who did (18.2 mL/min/Kg) groups were of borderline significance. No statistical differences were detected in the experimental propranolol pharmacokinetic parameters (maximal concentration, time of maximal concentration, terminal half-life, area under the curve, and protein binding) or derived pharmacokinetic parameters (intrinsic clearance, bioavailability, clearance, and volume of distribution). These results provide evidence that changes in aerobic fitness do not produce corresponding changes in propranolol pharmacokinetics in young or elderly adults.

Management of hypertensive urgencies and emergencies

Hypertensive emergency is a condition in which there is elevation of both systolic and diastolic blood pressure with the presence of acute target organ disease. Hypertensive urgency is a condition where the blood pressure is elevated (diastolic > 120 mmHg) with the absence of acute target organ disease. Hypertensive emergencies are best managed with parenteral drugs and careful intraarterial blood pressure monitoring. Hydralazine has been widely used in treatment of hypertension in eclampsia and preeclampsia, and its safety has been demonstrated in these patients. Sodium nitroprusside (SNP) has the most reliable antihypertensive activity, which begins immediately after its administration and ends when the infusion is stopped. As with diazoxide, it should be used with caution in patients with impaired cerebral flow. SNP is the preferred drug in obtaining controlled hypotension in patients undergoing neurovascular surgery. Intravenous nitroglycerin is useful in patients prone to myocardial ischemia, but should be avoided in patients with increased intracranial pressure. Esmolol is effective in controlling both supraventricular tachyarrhythmias and severe hypertension. Its short onset of duration of action make it useful in the emergent setting, but because of its negative inotropic effect its use should be avoided in patients with low cardiac output. Verapamil should not be used in patients with preexisting conduction abnormalities. Nicardipine is a potent arteriolar vasodilator without a significant direct depressant effect on myocardium. As with other afterload reducing agents, it should not be used in patients with severe aortic stenosis. Because angiotensin-converting enzyme (ACE) inhibitors generally cause cerebral vasodilatation, enalaprilat may be particularly beneficial for patients who are at high risk of developing cerebral hypotensive episodes secondary to impaired cerebral circulation. Fenoldopam, a selective post-synaptic dopaminergic receptor (DA1) has been shown to be effective in treating severe hypertension with a lower incidence of side effects than SNP. Hypertensive urgencies can usually be managed with oral agents. Oral nifedipine, captopril, clonidine, labetalol, prazosin, and nimodipine have all been shown to be effective in these situations.

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.

Cardiovascular and antiarrhythmic effects of esmolol in children

This prospective study evaluated the cardiovascular and antiarrhythmic effects of esmolol, an intravenous beta-blocker with an extremely short half-life. Twenty patients (aged 2 to 16 years) underwent diagnostic electrophysiologic studies at rest and during beta-blockade induced with esmolol. An initial dose of 600 micrograms/kg was infused for 2 minutes and followed by an infusion of 200 micrograms/kg per minute. The dosage was increased by 50 to 100 micrograms/kg per minute every 5 to 10 minutes until a reduction of greater than 10% in either heart rate or mean blood pressure was seen. The dosage required to achieve beta-blockade ranged from 300 to 1000 micrograms/kg per minute (mean 550 micrograms/kg per minute). Electrophysiologic effects included a decrease in the rate of sinoatrial node discharge and delay in conduction through the atrioventricular node. There was no effect on His-Purkinje conduction. Atrial and ventricular effective refractory periods were unchanged. In six patients with supraventricular tachycardia, esmolol prevented induction of tachycardia in four and slowed the rate of the tachycardia in two. In four patients with ventricular tachycardia, clinical findings were improved in three and unchanged in one. Heart rate and blood pressure returned to near baseline values 10 minutes after the esmolol infusion was stopped. Adverse ventricular electrophysiologic effects were observed in two patients with biopsy evidence of myocarditis. No other adverse effects were seen. We conclude that the effects of esmolol in children are similar to those of other beta-blockers and that it is useful in the evaluation and management of pediatric tachyarrhythmias. The weight-adjusted dosage required to induce beta-blockade in children is larger than the adult dosage, and the effects of esmolol dissipate rapidly.

Rapid-acting parenteral antihypertensive agents

Parenteral antihypertensive agents are useful in those clinical situations where rapid reduction of blood pressure is necessary or where treatment with oral antihypertensive medications is not feasible. Given the diverse selection of parenteral antihypertensive drugs now available, therapy can be individualized. The presence of concurrent diseases will often influence the decision-making process regarding choice of an agent. Complications of parenteral antihypertensive therapy can arise from the intrinsic properties of the various drugs or the development of severe hypotension. Gradual lowering of blood pressure, in conjunction with careful clinical evaluation, will minimize the risks of acute parenteral antihypertensive therapy. Given that parenteral antihypertensive therapy often needs to be replaced by oral therapy, those drugs that can be used both parenterally and orally may have an advantage.