Levosalbutamol in the treatment of asthma.
With the exception of levosalbutamol, all of the beta2-agonists that are currently in use are racemic mixtures that are composed in equal amounts of (R)- and (S)-enantiomers. Clinical and mechanistic studies have demonstrated that (R)-salbutamol alone provides the beta2-agonist activity that is needed for the relief of bronchoconstriction, as well as the beta2-adrenergically mediated side effects. (S)-Salbutamol, on the other hand, has minimal binding affinity for the beta2-receptor, indicating that its effects are likely to be mediated through another site. Furthermore, there is evidence that (S)-salbutamol opposes the desirable effects of (R)-salbutamol in the racemic mixture and contributes to the development of characteristic features of asthma, such as airway obstruction, bronchial hyperresponsiveness and airway inflammation. Evidence from clinical studies shows delayed recovery from exacerbation of asthma by patients who are exposed to high concentrations of (S)-salbutamol.