Effects of salbutamol and enantiomers on allergen-induced asthmatic reactions and airway hyperreactivity.

Salbutamol consists of a racemic mixture of R- and S-salbutamol. R-salbutamol (levalbuterol) is the active bronchodilating enantiomer, whereas S-salbutamol is thought to be pharmacologically inactive or to exert adverse effects. This study evaluated the bronchoprotective effects of inhalation of therapeutically relevant doses of the racemate and individual enantiomers in guinea pigs. It was found that basal airway reactivity to histamine was similarly reduced 30 min after inhalation of equivalent doses of RS- and R-salbutamol; this protective effect disappeared within 3 h. Inhalation of RS- and R-salbutamol 30 min before and 5.5 h after allergen challenge suppressed allergen-induced airway hyperreactivity to histamine after the early and late asthmatic reaction, completely inhibiting the early asthmatic reaction and tending to reduce the development of the late asthmatic reaction. At 5 h after allergen challenge, the inhibition of airway hyperreactivity was more pronounced in animals treated with R-salbutamol compared to racemate-treated animals. Both basal airway reactivity and allergen-induced hyperreactivity were not affected by S-salbutamol. Inflammatory cell infiltration was not affected by the racemate or the individual enantiomers. In conclusion, inhalation of therapeutically relevant doses of R- and RS-salbutamol effectively suppress allergen-induced airway reactivity after the early and late asthmatic reactions, the R-enantiomer being slightly more potent with respect to early airway reactivity than the racemate. No adverse effects were observed for the S-enantiomer.