Pharmacokinetics and pharmacodynamics of single oral doses of albuterol and its enantiomers in humans.

Albuterol (INN, salbutamol) is a beta 2-adrenergic receptor agonist widely used in the treatment of asthma. It is administered clinically as a racemic mixture, but only one enantiomer is active (eutomer) while the other (distomer) has been implicated in causing toxicity. This study used a chiral assay to compare the pharmacokinetics and pharmacodynamics of racemic albuterol with its two enantiomers in a three-way crossover of single oral doses in 12 healthy males. The bioavailability of the eutomer was less than that of the distomer after administration of pure enantiomers and racemate. Apart from causing a small increase in plasma potassium, the distomer had no effect on any pharmacodynamic parameter. The eutomer administered alone was significantly more potent than an equivalent dose given as racemate with regard to its effects on heart rate, QTc interval, plasma potassium levels, and plasma glucose levels. Despite this higher potency, the area under the plasma concentration versus time curve for eutomer after administration of pure eutomer was significantly lower than after administration of the racemate. This difference is probably the result of the more efficient metabolism of the eutomer in the absence of the distomer.