Levosalbutamol

Levosalbutamol (INN) or levalbuterol (USAN), trade name Xopenex, is the R-enantiomer of the short-acting β2-adrenergic receptor agonist salbutamol. It is marketed by Cipla as Levolin, & by axa named Axazest.

Uses
As a bronchodilator, it is used to treat asthma and Chronic obstructive pulmonary disease (COPD). In general, levosalbutamol has similar pharmacokinetic and pharmacodynamic properties to salbutamol; however, its manufacturer, Sepracor, has implied (although not directly claimed) that the presence of only the R-enantiomer produces fewer side effects.

Pharmacodynamics
Activation of beta2-adrenergic receptors on airway smooth muscle leads to the activation of adenylate cyclase and to an increase in the intracellular concentration of cyclic-3', 5' -adenosine monophosphate (cyclic AMP). The increase in cyclic AMP is associated with the activation of protein kinase A, which in turn, inhibits the phosphorylation of myosin and lowers intracellular ionic calcium concentrations, resulting in muscle relaxation.

Levosalbutamol relaxes the smooth muscles of all airways, from the trachea to the terminal bronchioles. Increased cyclic AMP concentrations are also associated with the inhibition of the release of mediators from mast cells in the airways. Levosalbutamol acts as a functional agonist that relaxes the airway irrespective of the spasmogen involved, thereby protecting against all bronchoconstrictor challenges. While it is recognized that beta2-adrenergic receptors are the predominant receptors on brochial smooth muscle, data indicate that there are beta-receptors in the human heart, 10-50% of which are beta2-adrenergic receptors. The precise function of these receptors has not been established. However, all beta-adrenergic agonist drugs can produce a significant cardiovascular effect in some patients, as measured by pulse rate, blood pressure, symptoms, and/or electrocardiographic (ECG).

Preference over salbutamol
The use of levosalbutamol over the more traditionally used racemic salbutamol is controversial among health care professionals. That using levosalbutamol instead of salbutamol produces less direct effect on β1-adrenergic receptors and/or fewer cardiac side effects has been suggested, but not consistently demonstrated by long term, well-designed clinical trials.

There are differing opinions on whether there is sufficient therapeutic benefit to using levalbuterol that outweighs the 5-10 times higher price tag. In general, it appears that if a clinician and patient feel that a low dose of racemic mixture is causing undesirable side effects, levalbuterol may be a viable alternative.

Approval
Levalbuterol was originally available only as a solution for nebulizer and eventually become available as a CFC-free metered dose inhaler under the trade name "Xopenex HFA (levalbuterol tartrate) Inhalation Aerosol". The FDA approval date was on March 11, 2005. (See Official FAQ)