Comparison of R-, S-, and RS-albuterol interaction with human beta 1- and beta 2-adrenergic receptors

Levalbuterol versus racemic albuterol in the treatment of acute exacerbation of asthma in children

OBJECTIVE

To compare levalbuterol and racemic albuterol for the treatment of acute exacerbation of asthma in pediatric population.

DESIGN

Prospective, double-blind, randomized research trial in a pediatric emergency department of an urban tertiary care hospital.

PARTICIPANTS

Children 5 to 21 years with a history of asthma presenting to the emergency department in acute exacerbation.

INTERVENTIONS

As per a computer-generated randomization sequence, patients received either 1.25 mg of levalbuterol or albuterol 2.5 mg via nebulization along with ipratropium hydrochloride. Patients received 3 back-to-back treatments as needed every 20 minutes, maximum of 3; 2 mg/kg of oral prednisone was administered to the patients after the second treatment. Baseline respiratory parameters such as oxygen saturations, respiratory rates, and peak flow rates were measured and repeated after every treatment.The decision for further treatments and or hospitalization was made by the treating emergency department physician as per his/her clinical judgement of the respiratory parameters at the end of 3 treatments.

RESULTS

Seventy patients completed the study. Most of the patients were in moderate severity of asthma exacerbation. All patients in both groups showed improvement in oxygen saturations, respiratory rates, and peak flow rates. However, no statistically significant difference was observed in the 2 groups regarding the respiratory parameters (P > 0.05).

CONCLUSION

Levalbuterol is not more efficacious than racemic albuterol in improving respiratory parameters in children presenting with acute exacerbation of asthma.

A preliminary comparison of levalbuterol and albuterol in prehospital care

Nebulized levalbuterol has been documented as more efficacious than albuterol in enhancing airflow in Emergency Department (ED) patients with bronchospasm. This work attempts to determine if nebulized levalbuterol yields similar improvements in peak flow measurements as those produced by albuterol in the Emergency Medical Services (EMS) arena. All adult EMS patients given a nebulized beta-agonist from January to June 2000 were included in this prospective, before-and-after, open-label study. Data collected included demographics, initial peak expiratory flow (PF), and use of home inhaled or nebulized bronchodilators before EMS arrival (PRE-TX). Outcome variable was the change in PF after a single EMS treatment with one of the study agents. Statistical analysis was performed using t-test and chi-square techniques; p was defined as 0.05. There were 298 patients enrolled; complete data for analysis were available for 196. Mean age was 68.0 years; 44.4% were male. Overall, albuterol produced a PF change of 19.7%; levalbuterol yielded a change of 20.4% (p = 0.9). In contrast to ED data, levalbuterol and albuterol produces similar changes in PF in the prehospital setting. Explanations for this finding may be linked to the pharmacokinetics of single vs. dual isomer preparations, and to the time frames of EMS care. Further efforts correlating EMS and ED data may better define the use of levalbuterol in prehospital care.

Clinically relevant concentrations of beta2-adrenergic agonists stimulate maximal cyclic adenosine monophosphate-dependent airspace fluid clearance and decrease pulmonary edema in experimental acid-induced lung injury

OBJECTIVE

To determine whether clinically relevant airspace concentrations of beta2-adrenergic agonists stimulated maximal alveolar fluid clearance rates and to determine whether beta2 agonist therapy decreased pulmonary edema in experimental acute lung injury.

DESIGN

Prospective randomized laboratory investigation.

SETTING

University-affiliated laboratory.

SUBJECTS

Sprague Dawley rats.

INTERVENTIONS

Dibutyryl cyclic adenosine monophosphate (cAMP), salmeterol, albuterol, and isoproterenol in normal rat lung. Salmeterol in a rat model of acid-induced lung injury.

MEASUREMENTS AND MAIN RESULTS

Basal alveolar fluid clearance was 7.6 +/- 2.2 %/hr. Maximal cAMP-dependent alveolar fluid clearance rate was 32.9 +/- 10.9 %/hr (p <.05). Racemic albuterol 10(-5) M, salmeterol 10(-6) M, and isoproterenol 10(-6) M each stimulated alveolar fluid clearance to a level comparable to maximal cAMP-dependent alveolar fluid clearance. Compared with basal rates, alveolar fluid clearance was increased by both racemic albuterol 10(-6) M (14.5 +/- 3.0%, p <.05) and R-enantiomer 10(-6) M (15.0 +/- 4.6%, p <.05), but there was no difference between the two groups. Intra-alveolar salmeterol 10 (-6) M attenuated the degree of pulmonary edema following acid-induced lung injury. Extravascular lung water increased to only 180 +/- 30 microL with salmeterol treatment, compared with 296 +/- 65 microL in saline-treated rats 4 hrs after acid injury (p <.05). This decrease in lung water was accompanied by a 2.4-fold increase in the rate of alveolar fluid clearance at 4 hrs in the salmeterol-treated group. Lung endothelial permeability, expressed as extravascular plasma equivalents, was reduced to 64 +/- 9 microL with salmeterol compared with 119 +/- 51 microL in saline-treated rats 4 hrs after acid injury (p <.05).

CONCLUSIONS

Clinically relevant airspace concentrations of beta2-adrenergic agonists a) stimulate maximal cAMP-dependent airspace fluid clearance in normal lungs and b) reduce pulmonary edema in acid aspiration-induced lung injury by increasing alveolar fluid clearance and decreasing endothelial permeability. Clinical studies are required to determine whether beta2-adrenergic agonists improve outcome in patients with acute lung injury.

(S)-Albuterol activates pro-constrictory and pro-inflammatory pathways in human bronchial smooth muscle cells

BACKGROUND

Pro-constrictory and proinflammatory properties of (S)-albuterol have been widely reported both under in vivo and in vitro conditions. However, underlying mechanisms are unclear.

OBJECTIVE

We examined and compared the cellular effects of albuterol enantiomers on key intracellular molecules involved in constrictory and inflammatory pathways in human bronchial smooth muscle cells (hBSMCs).

METHODS

Primary hBSMCs were grown in culture and treated with various concentrations of albuterol enantiomers for various periods. Methacholine was used to stimulate cells. The expression and activity of Gs and Gi proteins, the intracellular free calcium concentration ([Ca2+]i), the activity of phosphatidylinositol 3'-OH-kinase (PI3) kinase, and the transcriptional nuclear factor kappaB (NF-kappaB) level were examined.

RESULTS

There was a significant increase in the expression and activity of Gialpha-1 protein and a decrease in the expression of Gs protein in hBSMCs after 8 hours of treatment with (S)-albuterol. These effects of (S)-albuterol were observed in a dose-dependent manner. Nonreceptor-mediated activation of adenylate cyclase by forskolin was attenuated with (S)-albuterol. Treatment of the cells for 24 hours with (S)-albuterol significantly increased [Ca2+]i on stimulation with methacholine. Interestingly, the effect of (R)-albuterol was opposite to that of (S)-albuterol. The effect of the racemic albuterol in some cases was similar to that of (S)-albuterol. (S)-Albuterol significantly activated both PI3 kinase and NF-kappaB in hBSMCs.

CONCLUSION

These studies demonstrated an (S)-albuterol-induced increase in the expression and activity of pro-constrictory pathways involving Gialpha-1 protein and [Ca2+]i and a decrease in the activity of the bronchodilatory pathway involving Gs proteins in hBSNMCs. Additionally, (S)-albuterol activated proinflammatory pathways involving PI3 kinase and NF-kappaB. Because (S)-albuterol metabolizes at least 10-fold slower than (R)-albuterol and has a longer elimination half-life, these cellular effects of (S)-albuterol might explain the detrimental effect seen with chronic administration of racemic albuterol in the treatment of airway diseases, such as bronchial asthma.

Levalbuterol compared with racemic albuterol in the treatment of acute asthma: results of a pilot study

This was a prospective, open-label, nonrandomized pilot study to evaluate efficacy and tolerability of levalbuterol (LEV) in acute asthma. Asthmatics (forced expiratory volume in 1 second [FEV1], 20-55% predicted) were sequentially enrolled into cohorts of 12 to 14 and received 0.63, 1.25, 2.5, 3.75, or 5.0 mg LEV or 2.5 or 5.0 mg racemic albuterol (RAC) every 20 minutes x 3. After the first dose, FEV1 changes were 56% (0.6 L) for 1.25 mg LEV and 6% (0.07 L) and 14% (0.21 L) for 2.5 and 5 mg RAC respectively. After three doses, FEV1 changes were 74% (0.9 L), 39% (0.5 L), and 37% (0.6 L) for 1.25 mg, LEV 2.5 mg, RAC and 0.63 mg LEV respectively. LEV doses greater than 1.25 mg did not further improve bronchodilation. Baseline plasma (S)-albuterol levels were negatively correlated with baseline FEV1 (R = - 0.3, P = .004) and percent change in FEV1 (R = -0.3, P = .006). LEV at a dose of 1.25 mg produced effective bronchodilation that was greater than both RAC doses. The negative correlation between (S)-albuterol levels and FEV1 could suggest a deleterious effect of (S)-albuterol. Larger comparative studies are warranted.

Effect of inhaled racemic and (R)-albuterol on airway vascular smooth muscle tone in healthy and asthmatic subjects

Although the relative effect of racemic and (R)-albuterol on airway smooth muscle tone have been investigated in patients with airflow obstruction, the comparative effectiveness of these drugs in relaxing airway vascular smooth muscle is unknown. Therefore, we determined the actions of inhaled racemic and (R)-albuterol on airway mucosal blood flow (Qaw) normalized for anatomic dead space as an index of airway vascular smooth muscle tone in 11 healthy subjects and 10 subjects with mild asthma. We also monitored the forced expiratory volume in 1 second (FEV1) as an index of airway smooth muscle tone. Mean +/- SE baseline Qaw was 43.1 +/- 1.5 microl x min(-1) x ml(-1) in healthy subjects and 53.4 +/- 2.1 microl x min(-1) x ml(-1) in asthmatic subjects (p < 0.01). The corresponding values for FEV1 were 95.6 +/- 1.4 and 86.8 +/- 2.5% respectively, of predicted (p = 0.01). Racemic and (R)-albuterol caused a transient, dose-dependent increase of Qaw in healthy, but not in asthmatic subjects; the responses were not different between the two drugs. The FEV1 tended to increase more in asthmatics than in healthy subjects, again without a difference between the two drugs. These results show that racemic and (R)-albuterol have comparable effects on airway vascular smooth muscle and suggest that the blunted airway vascular smooth muscle response to albuterol in asthmatics is not related to (S)-albuterol.

Validation of a chiral HPLC assay for (R)-salbutamol sulfate

A fast, reliable and specific method for the screening, confirmation, determination and quantitation of salbutamol enantiomers was developed and validated. The described procedure includes a single robust chiral HPLC determination employing a Teicoplanin stationary phase. The method was evaluated for specificity, robustness, linearity, precision and accuracy. Under the chromatographic conditions of the method, known impurities were separated from the active principle.

Comparison of racemic albuterol and levalbuterol for treatment of acute asthma

OBJECTIVE

To determine whether levalbuterol resulted in fewer hospital admissions than racemic albuterol when used for treatment of acute asthma. Study design A randomized, double-blind, controlled trial was conducted in the emergency department (ED) and inpatient asthma care unit of an urban tertiary children's hospital. Children age 1 to 18 years (n=482) provided a total of 547 enrollments. Patients received a nebulized solution of either 2.5 mg racemic albuterol or 1.25 mg levalbuterol every 20 minutes (maximum six doses). Patients admitted to the asthma care unit were treated in a standardized fashion by using the same blinded drug assigned in the ED. Hospitalization rate was the primary outcome.

RESULTS

Hospitalization rate was significantly lower in the levalbuterol group (36%) than in the racemic albuterol group (45 %, P=.02). The adjusted relative risk of admission in the racemic group compared with the levalbuterol group was 1.25 (95% confidence interval, 1.01-1.57). Hospital length of stay was not significantly shorter in the levalbuterol group (levalbuterol, 44.9 hours; racemic albuterol, 50.3 hours; P=.63). No significant adverse events occurred in either group.

CONCLUSIONS

Substituting levalbuterol for racemic albuterol in the ED management of acute asthma significantly reduced the number of hospitalizations.

Levalbuterol: pharmacologic properties and use in the treatment of pediatric and adult asthma

LEARNING OBJECTIVES

To review the rationale supporting the use of levalbuterol [(R)-albuterol] for the treatment of pediatric and adult asthma.

DATA SOURCES

Peer-reviewed articles, selected abstracts from studies presented at recent professional meetings, and the Xopenex [levalbuterol, (R)-albuterol; Sepracor, Marlborough, MA] Summary Basis of Approval and package insert.

STUDY SELECTION

Institutional review board-approved clinical study protocols.

RESULTS

Levalbuterol is a single isomer beta2-agonist that differs from racemic albuterol by elimination of (S)-albuterol. Levalbuterol is an effective bronchodilator whose primary mechanism of action is unimpeded by (S)-albuterol. Thus, when compared with racemic albuterol, clinically comparable bronchodilation can be achieved with doses that substantially lessen beta-mediated side effects. In chronic or acute treatment of asthma, this favorable therapeutic profile cannot apparently be duplicated by increasing or decreasing the dose of racemic albuterol or by the addition of anticholinergic agents such as ipratropium bromide.

CONCLUSIONS

Levalbuterol seems to provide efficacy and safety advantages in pediatric and adult patients suffering from asthma. Its use may afford a cost benefit as well. More clinical studies are required to extend these observations for use in the treatment of other pulmonary diseases in both adults and children and to determine levalbuterol's impact on long-term therapy of respiratory diseases.

Evaluation of beta-adrenergic receptor subtypes in the human prostate cancer cell line-LNCaP

The present study was undertaken to determine the effects of catecholamines, agonists, and antagonists of beta-adrenergic receptors (AR) in the LNCaP cell line. Changes in cellular cyclic adenosine-3',5'-monophosphate (cAMP) levels were quantified by the use of a 6 cAMP response element (CRE)-luciferase reporter gene assay. LNCaP cells were transiently transfected with this gene construct, incubated in 96-well microtiter plates for 24 hr, and then treated with beta-AR agonists and/or antagonists for 4 hr. The rank order of potency for catecholamines and known beta-AR agonists was terbutaline(3.31 nM)>isoproterenol(8.31 nM)> or =fenoterol(15 nM)=epinephrine(16.2 nM)>norepinephrine(77.5 nM)>BRL-37344 [(R(*),R(*))-(+/-)4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxy acetic acid, sodium salt] (1000 nM)>dobutamine(1770 nM)>CGP12177 (4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazole-2-one hydrochloride) (inactive). The non-selective beta(1)-/-beta(2)-AR antagonists; propranolol and CGP 12177, at 10(-7)M, inhibited luciferase activity induced by these agonists by 80-96%. Propranolol blocked isoproterenol-induced luciferase responses in a competitive manner (K(B)=1.4 nM). In addition, isoproterenol-activated luciferase expression was blocked more potently by ICI 118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethy) amino]-2-butanol], a beta(2)-AR antagonist than by ICI 89,406 [(+/-)-N-[2-[3-(2-cyanophenoxy-)]-2-hydroxypropylamino]ethyl-N-phenylurea], a beta(1)-AR antagonist, giving K(B) values of 1.07 and 161nM, respectively. These results suggest that the beta(2)-AR is the major subtype mediating catecholamine-induced cAMP changes in LNCaP cells.

Single-isomer levalbuterol: a review of the acute data

Levalbuterol, the pure (R)-isomer of racemic albuterol, is a new therapeutic option for patients with asthma. Racemic albuterol comprises a 50:50 mixture of (R)- and (S)-albuterol, with (R)-albuterol conferring all of the bronchodilator effects of the racemate. Numerous preclinical and in vitro studies have indicated that (S)-albuterol is not an inert isomer, but may have proinflammatory effects. Results from clinical trials in adults and children with asthma have demonstrated that 0.63 mg levalbuterol provides effective bronchodilation with lower b-mediated side effects compared with 2.5 mg racemic albuterol. In the emergency department, levalbuterol provided greater bronchodilation and significantly reduced hospital admissions compared with racemic albuterol. Recent studies have supported that levalbuterol use in acute settings may reduce the cost of asthma treatment by decreasing the total treatments and subsequent respiratory therapy resources. Levalbuterol provides heath care professionals with a safe, effective, and potentially cost-saving alternative to racemic albuterol for the treatment of patients with asthma.

Effect of levalbuterol on prehospital patient parameters

This study was performed to determine if levalbuterol improves dyspnea as assessed by prehospital clinical parameters. All EMS patients >or=16 years old given nebulized levalbuterol over 6 months were included in this prospective, open-label work. Data collected included demographics, initial pulse rate (P), respiratory rate (R), patient report of respiratory distress (S), and peak expiratory flow (PF). Outcome variables were P, R, S, and PF after levalbuterol use. Statistical analysis used t tests, with P <or=.05. One hundred forty-seven patients were enrolled. Mean age was 65.9 years (62.6% women). Significant decreases in P, R, and S, and a significant increase in PF, were noted after levalbuterol administration. Levalbuterol produces significant improvement in EMS respiratory patient parameters. Tachycardia does not appear to be a side effect of levalbuterol administration. The results support the use of levalbuterol in prehospital care.

Effects of albuterol enantiomers on ciliary beat frequency in ovine tracheal epithelial cells

beta(2)-Adrenergic agonists stimulate ciliary beat frequency (CBF), an integral part of mucociliary clearance. To evaluate the differential effects of albuterol enantiomers and their racemic mixture on ciliary function, CBF and intracellular calcium were measured at room temperature from single ovine airway epithelial cells with use of digital videomicroscopy. Baseline CBF was 7.2 +/- 0.2 (SE) Hz (n = 80 measurements). R-albuterol (10 microM to 1 mM) stimulated CBF in a dose-dependent manner to maximally 24.4 +/- 5.4% above baseline. Racemic albuterol stimulated CBF to maximally 12.8 +/- 3.6% above baseline, a significantly lower increase compared with R-albuterol alone, despite identical R-enantiomer amounts in both groups. Simultaneous recordings of intracellular calcium concentration and CBF from single cells indicated that the CBF increase in response to R-albuterol was mediated through beta-receptors and stimulation of protein kinase A, in a calcium-dependent and -independent fashion. S-albuterol had a negligible effect on CBF and did not change intracellular calcium. Together, these results suggest that R-albuterol is more efficacious than racemic albuterol in stimulating CBF. Thus S-albuterol may interfere with the ability of R-albuterol to increase CBF.

Stereoselective pharmacokinetics and pharmacodynamics of anti-asthma agents

OBJECTIVE

To review the previously published studies on pharmacokinetics and pharmacodynamics of chiral drugs used in the treatment of asthma.

DATA SOURCES

Primary and review articles were identified with a MEDLINE search (1980-May 2001) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All English-language studies and reviews obtained from the MEDLINE search pertaining to stereoselective pharmacokinetics and pharmacodynamics of chiral anti-asthma drugs were assessed.

DATA SYNTHESIS

Several anti-asthma drugs (e.g., beta(2)-adrenergic agonists, leukotriene modifiers) are chiral and marketed as racemates, which consist of equal proportions of 2 enantiomers. Significant stereoselectivity has also been reported in pharmacodynamics and pharmacokinetics of the beta(2)-agonists. The enantiomers of beta(2)-agonists in the R configuration are primarily responsible for the bronchodilating effects of the racemate. The plasma concentrations of the enantiomers of anti-asthma drugs may differ as a reflection of stereoselectivity in clearance, volume of distribution, and route of administration.

CONCLUSIONS

Stereoselectivity in the pharmacokinetics of anti-asthma drugs may complicate the relationship between dose and/or plasma concentration of racemic drug versus effect relationship. An appreciation of the stereoselective pharmacokinetics and pharmacodynamics of chiral anti-asthma drugs may optimize the use of these agents in asthmatic patients.

Modulation of T-cell function by (R)- and (S)-isomers of albuterol: anti-inflammatory influences of (R)-isomers are negated in the presence of the (S)-isomer

BACKGROUND

beta(2)-Adrenergic agonists interact with specific receptors on T lymphocytes to mediate anti-inflammatory activities. However, anti-inflammatory effects are not observed when beta(2)-adrenergic agonists are administered in vivo as racemates.

OBJECTIVE

We hypothesized that anti-inflammatory influences are mediated by the (R)-isomer and are masked in the additional presence of the (S)-isomer.

METHODS

Antigen-specific T-cell lines were generated in the presence of recombinant human IL-2 and tetanus with or without varying concentrations of (R)- and (S)-isomers of albuterol alone or in combination. Parallel lines were generated in the presence of propranolol. Cells were briefly pulsed with PHA and evaluated for proliferation, apoptosis, and cytokine secretion.

RESULTS

(R)-Albuterol significantly inhibited T-cell proliferation (77.0% +/- 9.7% of control at 10(-8) mol/L and 61.1% +/- 9.0% at 10(-7) mol/L). No influence was observed with (S)-albuterol alone. However, the addition of (S)-albuterol to (R)-albuterol mediated a dose-dependent increase in proliferation. At equivalent concentrations of the 2 isomers, proliferation was unchanged from the control, whereas at 10(-6) mol/L (S)-albuterol, proliferation was enhanced. Both the inhibitory effects of (R)-albuterol alone and the stimulating influence of (R)- plus (S)-albuterol were blocked in the additional presence of propranolol. (R)-Albuterol at 10(-8) mol/L inhibited IL-2 and IFN-gamma production. Racemic albuterol (10(-8) mol/L each) had no influence on cytokine production; however, the combination of 10(-8) mol/L (R)-albuterol with 10(-6) (S)-albuterol stimulated production of IL-2 and IL-13. No effects were observed on apoptosis or cell viability.

CONCLUSION

These studies confirm the beta-adrenergic receptor-specific anti-inflammatory effects of (R)-albuterol. The racemate had minimal influences on proliferation or cytokine production. The presence of excess (S)-albuterol resulted in proinflammatory influences. We hypothesize that the (S)-isomer functions as an inverse agonist to switch the function of the beta(2)-adrenergic receptor.

Levalbuterol hydrochloride

Racemic albuterol, a commonly used bronchodilator, is an exact 50:50 mixture of two enantiomers, R- and S-albuterol. Concern regarding increased mortality associated with the use of this beta-2 (beta 2) agonist triggered the study of both of these enantiomers separately. In vitro studies suggest that the two enantiomers have different binding affinities for beta-adrenoreceptors, may exert opposing effects on inflammation, demonstrate different effects on mucocilary transport, and display differing pharmacokinetics. Clinical studies comparing both enantiomers are few, of short duration, and often in small patient populations, and their results vary. R-albuterol has greater bronchodilatory effects than the racemate and may have anti-inflammatory properties. S-albuterol has markedly less affinity for the beta-adrenoreceptor. It was found to cause bronchoconstriction in animal models, but neither bronchoconstrictive nor pro-inflammatory effects have been conclusively demonstrated in human studies. The data available at present, while suggestive, are insufficient to conclusively recommend R-albuterol over the racemate. Further basic research and investigations in humans comparing both enantiomers at increasing doses over longer time periods are required to clarify the precise roles of R- and S-albuterol.

Drug therapy approaches in the treatment of acute severe asthma in hospitalised children

Acute severe paediatric asthma remains a serious and debilitating disease throughout the world. The incidence and mortality from asthma continue to increase. Early, effective and aggressive outpatient therapy is essential in reducing symptoms and preventing life-threatening progression. When complications occur or when the disease progresses to incipient respiratory failure, these children need to be managed in a continuous care facility where aggressive and potentially dangerous interventions can be safely instituted to reverse persistent bronchospasm. The primary drugs for acute severe asthma include oxygen, corticosteroids, salbutamol (albuterol) and anticholinergics. Second-line drugs include heliox, magnesium sulfate, ketamine and inhalational anaesthetics. Future therapies may include furosemide, leukotriene modifiers, antihistamines and phosphodiesterase inhibitors. This review attempts to explore the multitude of medications available with emphasis on pharmacology and pathophysiology.

Low-dose levalbuterol in children with asthma: safety and efficacy in comparison with placebo and racemic albuterol

BACKGROUND

Racemic albuterol (RAC) is an equal mixture of (R)-albuterol and (S)-albuterol. Only the (R)-isomer, levalbuterol (LEV), is therapeutically active. Lower doses of LEV, devoid of (S)-albuterol, have demonstrated efficacy comparable to that of higher doses of the (R)-isomer administered as a component of RAC.

OBJECTIVE

The purpose of this study was to determine whether LEV results in improved safety and efficacy in children.

METHODS

Asthmatic children aged 4 to 11 years (n = 338; FEV(1), 40% to 85% of predicted) participated in this multicenter, randomized, double-blinded study and received 21 days of 3-times-a-day treatment with nebulized LEV (0.31 or 0.63 mg), RAC (1.25 or 2.5 mg), or placebo. The primary endpoint was FEV(1) (peak percent change). Adverse events, clinical laboratory test results, vital signs, and electrocardiograms were evaluated for safety.

RESULTS

All active treatments significantly improved the primary endpoint in comparison with placebo (P < .001). Significant differences in FEV(1) were noted immediately after nebulization (median change, 2.0%, 19.0%, 18.1%, 12.4%, and 15.6% for placebo, LEV 0.31 and 0.63, RAC 1.25 and 2.5 mg, respectively; P < .05 vs placebo; P < .05 for LEV 0.31 and 0.63 vs RAC 1.25 mg). LEV 0.31 mg was the only treatment not different from placebo for changes in ventricular heart rate, QT(c) interval, and glucose (P > .05). All active treatments decreased serum potassium (range, -0.3 to -0.6; P < .002 vs placebo), and RAC 2.5 mg caused the greatest change (P < .005 vs other actives). In a patient subset with severe asthma, a dose-response relationship was observed for levalbuterol, indicating that higher doses were more effective.

CONCLUSION

LEV was clinically comparable to 4- to 8-fold higher doses of RAC, and it demonstrated a more favorable safety profile. LEV 0.31 mg should be used as the starting dose in 4-11 year old children with mild to moderate persistent asthma. Patients with severe disease might benefit from higher doses.

The therapeutic ratio of R-albuterol is comparable with that of RS-albuterol in asthmatic patients

BACKGROUND

It has been suggested that R-albuterol produces bronchodilation that is comparable with that of racemic albuterol (RS-albuterol) on a 4:1 dose-for-dose basis but systemic side effects on a 2:1 basis, implying better therapeutic ratio for R-albuterol.

OBJECTIVE

We sought to carefully compare the bronchodilating and systemic effects of R- and RS-albuterol by using a crossover study design.

METHODS

Twenty asthmatic patients (15.1%-28.7% FEV(1) reversibility) were given R-albuterol (6.25-1600 microg), S-albuterol (6.25-1600 microg), RS-albuterol (12.5-3200 microg), or placebo in a crossover, double-blind, placebo-controlled fashion. Cumulative doses were given with a Mefar dosimeter, and FEV(1), heart rate, and plasma K(+) levels were measured 20 minutes after each dose.

RESULTS

Both R- and RS-albuterol produced dose-related improvement in FEV(1) and, at higher doses, increased heart rate and decreased plasma K(+) levels. Neither placebo nor S-albuterol had any significant effect. Individual estimates of the potency ratio for R-albuterol/RS-albuterol were calculated and summarized across all subjects. The geometric mean potency ratio for effects on FEV(1) was 1.9 (95% CI, 1.3-2.8), on HR of 1.9 (95% CI, 1.3-2.9), and on K(+) level of 1.7 (95% CI, 1.3-2.1).

CONCLUSION

All pharmacologic effects of RS-albuterol reside with the R-enantiomer, and S-albuterol is clinically inactive. The R-albuterol/RS-albuterol potency ratios for local (FEV(1)) and systemic effects (heart rate and K(+)) are similar, suggesting a comparable therapeutic ratio for R-albuterol and RS-albuterol in asthmatic subjects.

Acute asthma

OBJECTIVE: Asthma is the most common medical emergency in children. It is associated with significant morbidity and mortality rates and poses a tremendous societal burden worldwide. Management of the acute attack involves a stepwise approach that includes beta-agonist and steroid therapy, the mainstay of emergency treatment. Most patients will respond to this regime and can be discharged from the emergency department. Failure to respond to treatment necessitates hospital admission and sometimes admission to the intensive care unit (ICU). Management in the ICU involves intensification of pharmacologic therapy, including nonstandard therapies, in an attempt to avoid intubation and ventilation. When needed, mechanical ventilatory support can be rendered fairly safe with little morbidity if the likely cardiorespiratory physiologic derangements are appreciated and if appropriate ventilatory strategies are used. In the past two decades, the availability of newer potent medications and changes in approach to monitoring and ventilatory strategies have resulted in a decrease in ICU morbidity and mortality rates. Research endeavors are presently underway to further characterize the underlying mechanisms of the disease and are likely to lead to novel therapies. This article reviews the approach to management of acute severe asthma.

Single-isomer beta-agonists

A new generation of bronchodilators is being developed for acute asthma management-single-isomer beta-agonists. These drugs consist only of the active bronchodilatory isomer (eutomer); they do not have the inactive and potentially harmful isomer (distomer) that is present in marketed racemic beta-agonists. Clinical studies comparing the effectiveness of (R)-albuterol (levalbuterol) with racemic albuterol established a strong rationale for using single-isomer beta-agonists in place of the racemic mixture: reduced dosages provide equivalent bronchodilatory effects with fewer beta-mediated side effects. Higher dosages achieve superior bronchodilation in episodes of severe asthma and may reduce costs of emergency department treatment.

Enantioselective sulfation of beta 2-receptor agonists by the human intestine and the recombinant M-form phenolsulfotransferase

The beta 2-receptor agonist class of drugs is metabolized in humans almost exclusively by sulfate conjugation. The objective of this investigation was to determine the influence of chemical structure on the stereoselectivity of the sulfoconjugation of these chiral drugs. The pure enantiomers of six beta 2-agonists, including those clinically most widely used, were all effectively sulfated both by the cytosol of the human intestine and the recombinant human M-form phenolsulfotransferase (PST). Whereas the apparent Km values (Km,app) for the sulfation of the individual drug enantiomers by the intestinal cytosol varied widely, ranging from 4.8 microM for (S)-isoproterenol to 889 microM for (S)-albuterol, these Km,app values were highly correlated with those obtained with M-PST (correlation coefficient 0.994). In contrast, the M-PST Vmax,app values were similar for all drug enantiomers, ranging from 276 to 914 pmol min-1 mg-1 protein, implying that substrate binding to M-PST by far is the main determinant of the sulfation activity. For isoproterenol, the Km,app for M-PST was 6.1 times higher for the active (R)- than for the inactive (S)-enantiomer. For other beta 2-agonists, the stereoselectivity decreased towards unity as the Km,app increased. However, for albuterol, containing a hydroxymethyl substituent at the aromatic ring, the stereoselectivity was dramatically reversed, with 10 times higher Km,app for the inactive (S)- than for the active (R)-enantiomer.

Dose-response evaluation of levalbuterol versus racemic albuterol in patients with asthma

Albuterol, in all marketed forms, is sold as a racemate, composed of a 50:50 mixture of (R)- and (S)-isomers. Racemic albuterol and the single isomer version (R)-albuterol (levalbuterol) were compared in a randomized, double-blind, dose-ranging five-way crossover study in patients (n = 20) with mild persistent to moderate persistent asthma. Placebo, racemic albuterol (2.50 mg), or levalbuterol (0.31, 0.63, or 1.25 mg) were delivered as single, nebulized doses to 5 male and 15 female nonsmoking patients with asthma aged 18-50 years. Serial pulmonary function was assessed at 15-min intervals and mean time to onset of activity and duration of improvement of forced expiratory volume in 1 sec (FEV1) were measured. In addition, blood chemistries, electrocardiogram (ECG) readings, and patient subjective assessment of adverse symptoms were recorded. Levalbuterol was found to provide significant bronchodilatory activity and was well tolerated. Levalbuterol 1.25 mg provided the greatest increase and duration in FEV1 improvement, whereas racemic albuterol (2.50 mg) and levalbuterol 0.63 mg provided comparable effects. The lower doses of levalbuterol were associated with a less marked effect on heart rate and potassium than racemic albuterol or high-dose levalbuterol. These data suggest that 0.63 mg levalbuterol provides bronchodilation equivalent to 2.50 mg racemic albuterol with less beta-mediated side effects.

New millennium bronchodilators for asthma: single-isomer beta agonists

Racemic beta2 agonists are composed of a 50:50 mixture of R and S isomers. The R isomer exhibits virtually all the bronchodilation, whereas the S isomers are generally considered inert. However, (S)-albuterol was shown to enhance bronchial reactivity to methacholine, eosinophil activation, and histamine-induced influx of fluid, proteins, and neutrophils into the airspaces. Actions such as these may compress the potency and foreshorten the duration of (R)-albuterol. Accordingly, pure (R)-albuterol provides bronchodilation at lower doses than racemate, allowing for fewer beta-adrenergic-mediated side effects. In addition, differential metabolism may allow for the progressive accumulation of (S)-albuterol. This logic is applicable to long-acting beta2 agonists: the therapeutically active (R,R)-formoterol is currently being developed in the United States, and preliminary results suggest rapid improvements in FEV1 with up to 24-hour duration of action. These combined observations with the R isomers of beta2 agonists suggest that potential improvements in therapeutic indices can be achieved with isomerically pure versions of existing racemic drugs.

Pharmacokinetics and pharmacodynamics of cumulative single doses of inhaled salbutamol enantiomers in asthmatic subjects

Objectives of this study were to compare the pharmacokinetics, pharmacodynamics and safety of single cumulative doses of active (R)-salbutamol given either as the single enantiomer or racemic mixture by inhalation to subjects with mild to moderate asthma. This was a double-blind, crossover, cumulative-dose, randomized study where all subjects received either four doses of 1.25 mg of (R)-salbutamol or 2.5 mg of racemic (RS-) salbutamol by nebulization. The pharmacokinetic parameters were determined by noncompartmental analysis and model-fitting. Changes in FEV(1), plasma potassium, plasma glucose, heart rate, and QTc interval were measured. The potassium and glucose data were fitted to indirect response pharmacodynamic models. The heart rate and QTc data were evaluated using data descriptors. No significant differences in pharmacokinetics of (R)-salbutamol given as either (R)- or (RS)-salbutamol were found with AUC values of 11.90 +/- 4.37 and 11. 47 +/- 2.88 ng.h/ml. The t(max)of about 2 h reflected serial dosing rather than delayed absorption. The t(1/2)averaged about 3.5 h. The (S)-salbutamol showed AUC of 48.46 +/- 12.11 ng.h/ml with a t(1/2)of about 5 h. The changes in FEV(1)reached a plateau after an initial increase and did not return to pre-drug values for 10 h. All pharmacodynamic parameters were similar whether (R)- or (RS)-salbutamol was given. The exposure to (R)-salbutamol was identical after inhalation of (R) -and (RS)-salbutamol by subjects with asthma. Several pharmacological responses including FEV(1)were also similar and there were no unique safety concerns with either treatment.

Atopic diseases and upper respiratory infections

This article reviews information on the topics of asthma, allergic rhinitis, atopic dermatitis, food allergy, and upper respiratory infections. The asthma section includes a review of inhaled steroids and their potential side effects. New findings on the pathogenesis, triggers, and therapies of atopic dermatitis and new insights into food hypersensitivity reactions are presented. Recent publications in the areas of allergic rhinoconjunctivitis and upper respiratory infections are also reviewed.

Synergistic effects of neurotensin and beta-adrenergic agonist on 3,5-cyclic adenosine monophosphate accumulation and DNA synthesis in prostate cancer PC3 cells

Since neurotensin is often co-stored with catecholamines and since it can excite the release of dopamine and norepinephrine, responses to this peptide might depend upon the activity of catecholaminergic systems. In this study, we used prostate cancer PC3 cells, which express neurotensin receptors and 12-adrenergic receptors, to demonstrate that neurotensin can potentiate the effects of isoproterenol on 3',5'-cyclic adenosine monophosphate (cAMP) formation and on inhibition of DNA synthesis. While neurotensin had only a slight effect on basal cAMP levels, it nearly doubled the response to isoproterenol even at maximal levels without altering potency. Neurotensin increased the rate of cAMP accumulation and the steady-state level achieved. Consistent with the known antimitogenic action of dibutyryl-cAMP in PC3 cells, isoproterenol was found to inhibit DNA synthesis concentration-dependently, measured using [3H]thymidine. Neurotensin enhanced DNA synthesis when given alone. However, it inhibited DNA synthesis when given with a threshold level of isoproterenol, which by itself had no significant effect. These results, demonstrating cross-talk in the neurotensin and beta-adrenergic signaling pathways, suggest that there may be other physiologic instances of similar interactions between neurotensin and catecholamines.

Enantiomers of bronchodilating beta2-adrenoceptor agonists: is there a cause for concern?

All bronchodilating beta2-adrenoceptor agonists in current clinical use are derivatives of adrenaline and are available as racemates. Whereas the vast majority of the pharmacologic and clinical documentation has been made with the racemates, there are a few studies with the individual enantiomers. It thus appears that all established pharmacologic effects of racemic beta2-agonists reside in the (R)-enantiomer, with the (S)-enantiomer being virtually inactive. In recent years the suspicion has been raised that the (S)-enantiomer of the beta2-agonists is responsible for induction of airway hyperreactivity. This suspicion is based primarily on results obtained in guinea pigs exposed to (S)-enantiomers of beta2-agonists. A number of experiments in vitro have been undertaken to find a mechanism of action for these observations in vivo. Most of the results obtained are equivocal. However, the observation that (S)-salbutamol may cause mobilization of intracellular Ca2+, apparently by means of a cholinergic mechanism, deserves further investigation. The clinical studies are focused on the enantiomers of salbutamol. They confirm the preclinical findings that the pulmonary, as well as the extrapulmonary, effects of salbutamol reside in the (R)-enantiomer. The studies available so far do not convincingly show clinically significant airway hyperreactivity after exposure to the (S)-enantiomer. Further studies are needed to settle this issue.

The safety and efficacy of nebulized levalbuterol compared with racemic albuterol and placebo in the treatment of asthma in pediatric patients

BACKGROUND

Limited dose-response information is available for nebulized beta2 -agonists, especially in young children.

OBJECTIVE

The purpose of this study was to determine the safety and efficacy of increasing doses of nebulized levalbuterol (Xopenex; the pure R-isomer of racemic albuterol) and racemic albuterol compared with placebo in the treatment of asthma in pediatric patients.

METHODS

In this randomized, double-blind, crossover study, children (aged 3 to 11 years) with asthma (resting FEV1 50% to 80% of predicted normal [Polgar's] values) were treated with either levalbuterol, racemic albuterol, or placebo. Eligible subjects underwent a screening visit followed by 4 treatment visits. At each treatment visit, serial pulmonary function tests were completed before and after the treatment; plasma was collected to determine enantiomer levels, and safety was evaluated.

RESULTS

Five 3- to 5-year-old patients and twenty-eight 6- to 11-year-old patients completed the study, and a total of 87 doses of levalbuterol were administered. In the 6- to 11-year-old group, all doses of levalbuterol were significantly greater than placebo in peak change and percent peak change in FEV1 and area under the FEV1 versus time curve (P <.05). The FEV1 values over the 8-hour study period were similar for levalbuterol 0.31 and 0.63 mg and racemic albuterol 2.5 mg and were greatest after levalbuterol 1.25 mg. Median plasma levels of R-albuterol depended on dose and were 0.4, 0.7, 1.2, and 1.0 after levalbuterol 0.31 mg, 0.63 mg, and 1.25 mg and racemic albuterol 2.5 mg, respectively. All patients in the 2.5-mg racemic albuterol arm had measurable plasma levels of S-albuterol, although S-albuterol levels were undetectable in most patients in the levalbuterol arms. In a few patients who received levalbuterol, S-albuterol levels were detected, which was likely because of the use of racemic albuterol as a concomitant medication. All active treatments were well tolerated. beta-Mediated changes in heart rate, potassium, and glucose were dose dependent for all active treatment groups.

CONCLUSION

Levalbuterol caused a significantly greater increase in FEV1 than placebo, and FEV1 values were comparable with or better than those observed with racemic albuterol. beta-Mediated side effects were lower for an equipotent dose of levalbuterol when compared with racemic albuterol. Treatment with levalbuterol resulted in plasma levels that were dose dependent and had an approximate correlation with pharmacodynamic parameters.

Neurotensin enhances agonist-induced cAMP accumulation in PC3 cells via Ca2+ -dependent adenylyl cyclase(s)

A human prostate cancer cell line (PC3) with abundant neurotensin (NT) receptors was used to demonstrate that NT potentiated 3',5'-cyclic adenosine monophate (cAMP) accumulation in response to a variety of stimuli, including both direct forskolin (F) and indirect (prostaglandin, (PGE2), isoproterenol (ISO) and cholera toxin (CTx)) activators of adenylyl cyclase. Several mechanisms were investigated and our results indicated an effect on the rate of cAMP formation and not on degradation or extrusion. For each stimulus, NT enhanced efficacy without altering EC50. The effect of NT did not involve stimulatory G-protein (Gs)-activation or interference with a tonic inhibitory G-protein (Gi)-mediated inhibition. A similar response was obtained when NT was added with the stimulus or given as a two minute pulse which was removed prior to addition of stimulus. The potentiating activity disappeared with a t1,2 of approximately 15 min. NT transiently elevated cellular [Ca2+]i and its effects on cAMP could be mimicked by [Ca2+]i-elevating agents (uridine triphosphate (UTP), thapsigargin and ionomycin). Buffering cellular [Ca2+]i with 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) inhibited cAMP responses to ISO and F in presence and absence of NT. These data support the idea that NT potentiated cAMP formation in response to a variety of stimuli by facilitating the activation of Ca2+ -dependent adenylyl cyclases.