Albuterol enantiomer levels, lung function and QTc interval in patients with acute severe asthma and COPD in the emergency department

Long-Acting β2-Agonists in Asthma: Enantioselective Safety Studies are Needed

Long-acting β2-agonists (LABAs) such as formoterol and salmeterol are used for prolonged bronchodilatation in asthma, usually in combination with inhaled corticosteroids (ICSs). Unexplained paradoxical asthma exacerbations and deaths have been associated with LABAs, particularly when used without ICS. LABAs clearly demonstrate effective bronchodilatation and steroid-sparing activity, but long-term treatment can lead to tolerance of their bronchodilator effects. There are also concerns with regard to the effects of LABAs on bronchial hyperresponsiveness (BHR), where long-term use is associated with increased BHR and loss of bronchoprotection. A complicating factor is that formoterol and salmeterol are both chiral compounds, usually administered as 50:50 racemic (rac-) mixtures of two enantiomers. The chiral nature of these compounds has been largely forgotten in the debate regarding LABA safety and effects on BHR, particularly that (S)-enantiomers of β2-agonists may be deleterious to asthma control. LABAs display enantioselective pharmacokinetics and pharmacodynamics. Biological plausibility of the deleterious effects of β2-agonists (S)-enantiomers is provided by in vitro and in vivo studies from the short-acting β2-agonist (SABA) salbutamol. Supportive clinical findings include the fact that patients in emergency departments who demonstrate a blunted response to salbutamol are more likely to benefit from (R)-salbutamol than rac-salbutamol, and resistance to salbutamol appears to be a contributory mechanism in rapid asthma deaths. More effort should therefore be applied to investigating potential enantiospecific effects of LABAs on safety, specifically bronchoprotection. Safety studies directly assessing the effects of LABA (S)-enantiomers on BHR are long overdue.

Effect of Ventolin on QTc in children with respiratory distress

INTRODUCTION

β2-agonists are first election drugs for the treatment of respiratory disease that may alter cardiac autonomic modulation. The aim of this study was to evaluate the effects of nebulized Ventolin on electrocardiogram, particularly QTc interval to assess the potential arrhythmogenic risks.

METHODS

A total of 192 patients between 2 months and 15 years which received nebulized Ventolin were enrolled in this study. Patients were divided into two groups. Electrocardiograms of patients before and after nebulized Ventolin were taken. Differences between two groups were assessed using a paired student's t test.

RESULTS

There was statistically significant differences in QTc before and after Ventolin in each groups (P<0.005).Ventolin effect on QTc interval in both groups did not differ. In first group, there was statistically significant differences between heart rate before and after Ventolin taken (P=0.009) but in second group there was not statistically significant differences between heart rate (P=0.345).

CONCLUSION

Although Ventolin can cause changes in QTc, Ventolin with 0.15 mg/kg/dose in comparison with 0.1 mg/kg/dose does not cause significant changes in QTc.

Diastolic hypotension in pediatric patients with asthma receiving continuous albuterol

OBJECTIVES

Concerns have been raised regarding cardiac side effects of continuous high-dose albuterol nebulization in status asthmaticus management. Our study goal was to determine prevalence and potential risk factors for hypotension development during continuous albuterol administration in pediatric patients.

METHODS

A retrospective cohort study was conducted at Children's Memorial Hermann Hospital from 1 January 2011 to 31 August 2012. A total of 152 patients admitted to pediatric intensive or intermediate care units who received continuous albuterol nebulization for management of status asthmaticus were analyzed.

RESULTS

Diastolic hypotension, defined as a value < 50 mmHg or <5th percentile of normal for age, developed in 90% of patients and a positive correlation with increasing doses of albuterol was demonstrated. The overall median time to onset of hypotension was 4 h (interquartile range (IQR): 2-6.5) and was significantly lower among patients admitted to the intensive care unit rather than intermediate care (p = 0.005). The odds of hypotension were 82% lower among patients who received fluid boluses prior to continuous albuterol nebulization. None of the potential risk factors demonstrated statistical significance.

CONCLUSIONS

Diastolic hypotension is a common occurrence among patients who receive continuous albuterol nebulization for status asthmaticus. Total albuterol dose appeared to be directly related to risk of developing diastolic hypotension. Administration of supplemental fluid boluses before continuous nebulized albuterol appeared to provide a significant protective effect. The clinical impact and the significance of diastolic hypotension and the importance of prophylactic administration of intravenous fluid boluses in patients experiencing status asthmaticus are yet to be determined.

Enantioselective disposition of (R/S)-albuterol in skeletal and cardiac muscle

Significant enhancement of skeletal muscle function has been observed with racemic albuterol (salbutamol). There is now general acceptance that the R-albuterol enantiomer elicits the pharmacological response, both in the lungs and extrapulmonary, while S-albuterol is pharmacologically inert. The objective of this study was to investigate the distribution of (R/S)-albuterol enantiomers into skeletal and cardiac muscle. Initially oral dosing was undertaken in neonatal mice administered a maximum tolerable dose of racemic albuterol. An in vivo infusion rat model was employed for the investigation of albuterol uptake into skeletal and cardiac muscle over 4 h. Tissue concentrations were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). From the oral dosing model, mean (±SD) levels of racemic albuterol after 5 days were 915 (±293) ng/mL in plasma, 2574 (±196) ng/g in muscle, and 53 (±6.6) ng/g in brain with enantioselective partitioning (muscle:plasma ratio of 5.7 and 1.7 for R- and S-albuterol, respectively). In the infusion model, enantioselective disposition was observed in skeletal muscle (muscle:plasma ratio of 1.2-1.7 and 0.6-0.7 for R- and S-albuterol, respectively) and in cardiac muscle (4.1 and 0.5, respectively). In conclusion, there is greater partitioning of active (R)-albuterol than inactive (S)-albuterol into both skeletal and cardiac muscle compared to plasma. These findings have relevance for albuterol sports doping, cardiac effects, and therapeutic use in muscle wasting diseases. Furthermore, the greater muscle partitioning of the active R-albuterol, and the availability of pure R-albuterol formulations highlight shortcomings in doping control measures using non-enantioselective assays.