Pharmacokinetic studies with inhaled drugs.

In the past decade there have been a number of studies of the pharmacokinetics and metabolism of drugs used in the treatment of asthma. The influence of route of administration on metabolism was first noted in studies with isoprenaline and then extended to other adrenaline-like beta-adrenoceptor agonists including isoetharine, terbutaline and salbutamol. Later studies with disodium cromoglycate and recent studies on glucocorticoids such as beclomethasone and budesonide have confirmed the importance of route of administration in the kinetics and metabolism of anti-asthmatic drugs. Thus, although there are differences in routes of metabolism, the selectivity of action within the airways when the drugs are inhaled is to a large part dependent on pharmacokinetic and metabolic factors.