Anomalous effects of albuterol and other sympathomimetics in the guinea pig

A prospective randomized controlled blinded study of three bronchodilators in infants with respiratory syncytial virus bronchiolitis on mechanical ventilation

OBJECTIVE

To study patients with respiratory syncytial virus bronchiolitis in respiratory failure to make specific measurements reflecting airway resistance before and after treatment with commonly used agents. We hypothesized that racemic epinephrine would decrease airways resistance more effectively than levalbuterol, and levalbuterol would decrease airways resistance more effectively than racemic albuterol. Normal saline was used as a control.

DESIGN

Prospective, randomized, controlled, blinded study.

SETTING

Tertiary Pediatric Intensive Care Unit in a University affiliated hospital in the northeastern United States.

PATIENTS

Twenty-two patients with respiratory syncytial virus bronchiolitis and in respiratory failure were enrolled. All were intubated and ventilated in a volume control mode and sedated.

INTERVENTIONS

In a randomized, blinded fashion patients were given four agents: norepinephrine, levalbuterol, racemic albuterol, and normal saline at 6 hr intervals.

MEASUREMENTS

As indicators of bronchodilation, peak inspiratory pressure and inspiratory respiratory system resistance were measured before and 20 mins after each agent was given. Thus, each patient acted as his/her own control.

MAIN RESULTS

There were small but statistically significant decreases in peak inspiratory pressure after racemic epinephrine treatment, levalbuterol, and racemic albuterol. There was no change in peak inspiratory pressure after inhaled normal saline. Inspiratory respiratory system resistance fell significantly after all treatments, including saline. Heart rate rose significantly after inhaled bronchodilator treatments (p < 0.05 for all treatments).

CONCLUSIONS

Similar statistically significant bronchodilation occurred after all three bronchodilators as indicated by a decrease in peak inspiratory pressure and respiratory system resistance, but these changes were small and probably clinically insignificant. However, side effects of bronchodilators, such as tachycardia, also occurred, and these may be clinically significant. Thus the benefit of bronchodilator treatment in these patients is small, does not differ among the drugs we studied and of questionable value.

A comparison of levalbuterol with racemic albuterol in the treatment of acute severe asthma exacerbations in adults

This multicenter, randomized, double-blind trial compared nebulized levalbuterol (Lev) and racemic albuterol (Rac) in the treatment of acute asthma.

METHODS

Adults with acute asthma exacerbations (FEV(1) 20%-55% predicted) received prednisone and either Lev (1.25 mg, n = 315) or Rac (2.5 mg, n = 312). Nebulized treatments were administered every 20 minutes in the first hour, then every 40 minutes for 3 additional doses, then as necessary for up to 24 hours. The primary end point was time to meet discharge criteria. Secondary end points included changes in lung function and hospitalization rates. A subset of 160 patients had plasma (S)-albuterol concentrations determined at study entry.

RESULTS

Time to meet discharge criteria did not differ between the 2 treatments. FEV(1) improvement was greater following Lev compared with Rac, both after dose 1 and cumulatively over the entire treatment period (dose 1 in intent to treat [ITT] group: Lev 0.50 +/- 0.43 L, Rac 0.43 +/- 0.37 L; P = .02), particularly among the 60% of patients not on recent steroid therapy (dose 1: Lev 0.58 +/- 0.47 L, Rac 0.44 +/- 0.37 L; P < .01), and patients whose entry (S)-albuterol concentrations were in the highest quartile of those measured. A small and similar proportion of Lev-treated (7.0%) and Rac-treated (9.3%) patients required hospitalization (P = .28). Among patients not on steroids, fewer Lev- than Rac-treated patients required admission (3.8% vs 9.3%, P = .03), as was also the case for patients with high plasma (S)-albuterol concentrations. Asthma relapses (5% in 30 days) were lower than in previous reports and did not differ between groups.

CONCLUSIONS

This study suggests that early, regular nebulized beta(2)-agonist and systemic corticosteroid therapy may reduce hospitalization and relapse rates in patients with acute severe asthma. Lev was well tolerated and compared favorably with Rac in improving airway function, particularly in those who were not on inhaled or oral corticosteroids and in those who had high plasma (S)-albuterol concentrations at presentation.

Population pharmacokinetics of (R)-albuterol and (S)-albuterol in pediatric patients aged 4-11 years with asthma

OBJECTIVE

To characterize the population pharmacokinetics (PK) of (R)- and (S)-albuterol in pediatric asthmatics using a model that supports a sparse blood sampling strategy.

METHODS

The data for this analysis were collected from patients enrolled in a randomized, double-blind, multicenter, placebo- and active-controlled study evaluating the safety and efficacy of levalbuterol in asthmatic children aged 4-11 years. Patients received either levalbuterol 0.31 mg, levalbuterol 0.63 mg, racemic albuterol 1.25 mg, or racemic albuterol 2.5 mg via nebulizer. Separate population pharmacokinetic models were developed for (R)- and (S)-albuterol using the NOMNEM((R)) computer program. Covariate models were developed to identify significant predictors of inter-patient variability.

RESULTS

A total of 995 samples and 262 patients were used for the (R)-albuterol population PK model while a total of 496 samples and 128 patients were used for the (S)-albuterol population PK model. The apparent clearance of (R)-albuterol was much more rapid than that of (S)-albuterol (approximately four-fold higher), and the apparent volume of distribution was much larger for (R)-albuterol (in part due to pre-systemic metabolism) than for (S)-albuterol (approximately four-fold higher).

CONCLUSIONS

In this study of pediatric patients, the models were able to demonstrate using two to four samples per patient that the apparent clearance and volume of distribution of (R)-albuterol were several fold higher than that of (S)-albuterol. The pharmacokinetics of (R)-albuterol were similar after administration of levalbuterol or racemic albuterol and were linear over the examined dose range (0.31-0.63 mg nebulized dose). The presence of (S)-albuterol did not significantly alter the pharmacokinetics of (R)-albuterol, suggesting that effects of (S)-albuterol may be due to the intrinsic pharmacology of this isomer.

The pursuit of precision pharmaceuticals: divergent effects of beta2 agonist isomers

Beta2 agonists are the most commonly used treatment for acute bronchoconstriction. However, during regular use there is a progressive decline of protective efficacy of bronchodilators. This progressive decline has long been considered anomalous because with short-acting beta agonists, there is no corresponding change in bronchodilator efficacy. Airway hyper-responsiveness is itself a feature of asthma and there maybe however, there may be an increase in airway hyper-responsiveness following regular use of beta2 agonist. Airway hyperresponsiveness could diminish the capacity of beta agonists to protect from or result in paradoxical bronchospasm and there effects of racemic salbutamol. There have been reports of increased morbidity and mortality associated with excessive use of beta(2) agonists. As all beta agonists used clinically are racemates composed of 1:1 mixtures of R and S isomers, conducted on the possible involvement of the isomers in hyper-responsiveness. Hyper-responsiveness cannot be attributed to the R isomer, whose capacity to activate beta adrenoceptors will nullify this effect. In contrast, extensive evidence indicated that the S isomer might cause hyper-responsiveness and potential airway inflammation. Further, the S isomer shows a propensity to activate human eosinophils and alter muscarinic M(2) receptor functions. The S isomer, which makes no contribution to therapeutic efficacy and may exacerbate asthma, might therefore be excluded from asthma therapy.

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.

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.

Levalbuterol compared to racemic albuterol: efficacy and outcomes in patients hospitalized with COPD or asthma

STUDY OBJECTIVES

To compare clinical efficacy, patient outcomes, and medical costs in hospitalized patients treated with levalbuterol to those treated with racemic albuterol.

DESIGN

Retrospective chart review.

SETTING

A 180-bed community hospital.

PATIENTS

Patients admitted to Halifax Regional Hospital with a diagnosis code for COPD or asthma from July 1 to December 31, 1998, and from July 1 to December 31, 1999, were eligible. In 1998, 125 patients were treated with nebulized racemic albuterol (2.5 mg q4h). In 1999, 109 patients were treated with levalbuterol (1.25 mg q8h).

MEASUREMENTS AND RESULTS

Clinical efficacy was evaluated by the number of nebulizer treatments, improvement in symptoms and objective clinical findings, the length of hospital stay, and hospital discharge disposition. Medication and total hospital costs were calculated based on Red Book listings and Medicare reimbursement rates. Levalbuterol-treated patients required significantly fewer treatments with beta-agonists (mean [+/- SD] number of treatments, 19.0 +/- 12.7 vs 30.8 +/- 24.0; p < 0.001) and ipratropium bromide (mean number of treatments, 9.4 +/- 11.5 vs 23.2 +/- 25.1; p < 0.001) than did racemic albuterol-treated patients. The mean length of hospital stay in the levalbuterol group was almost 1 day less than that in the racemic albuterol group (4.7 +/- 2.9 vs 5.6 +/- 4.2 days, respectively; p < 0.058). Significantly more patients were readmitted to the hospital within 30 days in the racemic albuterol group compared with the levalbuterol group (16.4% vs 5.7%, respectively; p = 0.01). The mean total cost of nebulizer therapy was significantly greater for patients receiving racemic albuterol than for those receiving for levalbuterol ($112 +/- 101 vs $61 +/- 43, respectively; p < 0.001). The mean total hospital costs per patient were less for levalbuterol compared with racemic albuterol ($2756 +/- 2079 vs $3225 +/- 2714, respectively; p = 0.11). Regression analysis controlling for diagnosis, baseline FEV(1), and ipratropium use indicated that levalbuterol was associated with a length-of-stay savings of 0.91 days (p = 0.015), a total cost savings of $556 (p = 0.013), and a decrease in the likelihood of hospital readmission of 67% (p = 0.056).

CONCLUSION

Compared with patients treated with racemic albuterol, those treated with levalbuterol required less medication, had shorter lengths of hospital stay, had decreased costs for nebulizer therapy and hospitalization, and appeared to have a more prolonged therapeutic benefit. These findings support using levalbuterol as first-line therapy for hospitalized adults with COPD or asthma.

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.

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.

Measurement of albuterol in guinea pig serum by high performance liquid chromatography with fluorescence detection

A sensitive, simple and reproducible high performance liquid chromatographic method for detecting and quantifying albuterol in guinea pig serum is described. A structurally related compound, bamethan, was used as an internal standard. The method employs ion-pair extraction with di(2-ethylhexyl)phosphate followed by chromatography on a Zorbax SB C18 reversed-phase column. Fluorescence detection was used to identify the compounds of interest. The calibration curve was linear between 1 and 50 ng/mL albuterol hemisulfate salt (0.83 and 41.50 ng/mL albuterol base), and the limit of detection for a 1 mL sample was 1 ng/mL albuterol hemisulfate salt (0.83 ng/mL albuterol base). Serum levels of albuterol were quantified from guinea pigs that had received the drug by continuous subcutaneous infusion at a dose of 0.2 mg/kg/day for 1, 5 or 10 days, or 10 days followed by a 24 h washout period.

Preferential pulmonary retention of (S)-albuterol after inhalation of racemic albuterol

The (R)-enantiomer of racemic albuterol produces bronchodilation, whereas the (S)-enantiomer may increase airway reactivity. After oral or intravenous administration of racemic albuterol, the (R)- enantiomer is metabolized several times faster than the (S)-enantiomer; however, enantiomer disposition after inhaling racemic albuterol with a metered-dose inhaler (MDI) is not known. Accordingly, 10 healthy subjects inhaled racemic albuterol with a MDI alone and with a MDI and holding chamber. We measured plasma levels of unchanged (R)- and (S)-albuterol before and up to 4 h after inhalation of racemic albuterol, and determined the unchanged R/S ratio in urine before and at 0.5, 4, 8, and 24 h later. The disposition of albuterol's enantiomers with a MDI and holding chamber was similar to that with a MDI alone. The area under the curve (AUC) of the plasma levels over time was significantly lower for the (S)- than for the (R)-enantiomer-395.5 +/- 141.0 (SE) versus 882.7 +/- 126.4 ng. ml(-)(1). min (p < 0.05)-indicating preferential retention of (S)-albuterol in the lung. The R/S ratio in urine at 0. 5 h after albuterol was > 1, reflecting the higher plasma level of the (R)-enantiomer. In conclusion, preferential retention of the (S)- compared with the (R)-enantiomer in the lung could lead to accumulation of the (S)-enantiomer after long-term use of racemic albuterol.

Sympathomimetic enantiomers and asthma

Airways of asthma patients can become hyperresponsive to airway spasmogens following regular use of isoprenaline or beta 2-selective sympathomimetics. Hyper-reactivity that results from acute exposure of animals to these drugs is pre-empted by vagal section (a procedure which does not influence spasmolytic efficacy of sympathomimetics), is not diminished by antagonism of beta 2-adrenoceptors and is not associated with loss of responsivity of beta 2-adrenoceptors in the airways. Since activation, modulation, or blockade of beta 2-adrenoceptors does not determine this form of hyperreactivity, the possibility that distomers may induce hyperreactivity must be considered. Ocular and vascular responses to distomers of sympathomimetics have long been recognised and, more recently, comparable observations have been made for the airways. Thus, reactivity of guinea-pig airways to spasmogens was increased following exposure to S-isoprenaline, S-salbutamol, or S-terbutaline and exposure to S-isoprenaline or S-salbutamol can intensify symptoms in asthmatics. Regular exposure to the racemate, especially during or following an allergic reaction, predisposes to expression of hyper-reactivity, which is nullified, acutely, by the eutomer. These observations imply that biological effects of sympathomimetic distomers may contribute to morbidity and mortality in asthma patients.

Effects of the enantiomers of R,S-salbutamol on incompletely fused tetanic contractions of slow- and fast-twitch skeletal muscles of the guinea-pig

1. The effects of racemic R,S-salbutamol, and its individual enantiomers have been studied on incompletely fused (sub-tetanic) contractile responses of fast- and slow-contracting isolated skeletal muscles of the guinea-pig. 2. R,S-salbutamol (2-4 microM) decreased the peak force of sub-tetani in the slow-contracting soleus muscle and increased the peak force of sub-tetani in the fast-contracting peroneus longus muscle. It also increased the force of the first twitch of sub-tetani in both muscles. The decrease in the peak force of sub-tetani in the soleus muscle was due to defusion of the individual twitches caused by a shortening of their time course. 3. The effects of 4 microM of the racemate on both fast- and slow-contracting muscles were mimicked by 2 microM R-salbutamol (levalbuterol). However, 2 microM S-salbutamol was devoid of activity in both muscles. 4. We concluded that all the effects of R,S-salbutamol on guinea-pig skeletal muscles are due to the activity of the R-enantiomer. Thus there is a common enantiomeric profile for the skeletal muscle and bronchorelaxant activity of the compound.

Effect of single doses of S-salbutamol, R-salbutamol, racemic salbutamol, and placebo on the airway response to methacholine

BACKGROUND

Commercially available salbutamol is a racemic mixture consisting of equal amounts of the two enantiomers, R-salbutamol and S-salbutamol, felt to be active and inert, respectively.

METHODS

A double blind, randomised, four way, crossover study was performed in 12 well controlled asthmatic subjects (forced expiratory volume in one second (FEV1) > 70% predicted, no beta 2 agonists for > or = 4 weeks). Subjects were studied on four days at intervals of 48 hours to seven days. FEV1 was assessed before and both FEV1 and methacholine PC20 were measured 20 and 180 minutes after a single dose of nebulised racemic salbutamol 2.5 mg, R-salbutamol 1.25 mg, S-salbutamol 1.25 mg, and placebo.

RESULTS

Equivalent bronchodilation was seen for both R-salbutamol and racemic salbutamol (mean (SE) 12.4 (3.1)% and 12.0 (3.0)%, respectively, at 20 minutes and 5.9 (2.9)% and 5.2 (2.2)% at 180 minutes). The increase in FEV1 of 5.2 (0.9)% at 20 minutes and the decline in FEV1 of 2.9 (2.1)% at 180 minutes after S-salbutamol were not significantly different from the placebo response. Compared with placebo the methacholine PC20 after R-salbutamol and racemic salbutamol improved by 3.3 (95% CI 2.5 to 4.1) and 3.4 (95% CI 2.6 to 4.2) doubling doses, respectively, at 20 minutes and 1.2 (95% CI 0.6 to 1.8) and 1.0 (95% CI 0.2 to 1.8) doubling doses at 180 minutes. S-salbutamol resulted in an improvement of 0.9 (95% CI 0.3 to 1.5) doubling doses at 20 minutes and no change at 180 minutes. Restlessness (n = 11) and increased pulse were seen 20 minutes after racemic and R-salbutamol but not S-salbutamol or placebo, and not at 180 minutes. There were no other adverse events.

CONCLUSION

A single dose of 1.25 mg nebulised R-salbutamol produced equivalent bronchoprotection, bronchodilation, restlessness, and tachycardia as did 2.5 mg of racemic salbutamol. S-salbutamol 1.25 mg had a weak bronchoprotective effect; this could be because of a small amount of contamination with R-salbutamol or because S-salbutamol is an intrinsically weak beta 2 receptor stimulant.