Optimizing inhaled drug delivery in patients with asthma.

Successful management of asthmatic patients depends on achieving adequate delivery of inhaled drugs to the lung. This assumes particular importance for inhaled corticosteroids where the therapeutic goal should be to achieve a high ratio of airway anti-inflammatory efficacy to local and systemic side effects. The availability of user-friendly inhaler devices requires a critical appraisal of their effectiveness and an evaluation of whether improved lung deposition of anti-asthma drugs translates into improved clinical efficacy. There is evidence to suggest that the routine use of large-volume spacers for inhaled corticosteroids may not be the best first-line option, in that reduced drug delivery is associated with multiple actuations, inhalation delay and the presence of static electricity. Breath-actuated pressurized aerosol devices or dry powder inhaler devices may be a better option for many asthmatic patients, although the efficiency of drug delivery varies considerably between these devices. There is good evidence with a reservoir dry powder inhaler device to show that improved lung deposition translates into better therapeutic response, both in terms of beta 2-agonist and corticosteroid delivery. For inhaled corticosteroids, such as fluticasone propionate and budesonide, there is evidence to show that systemic bioactivity is mainly determined by lung bioavailability rather than gastrointestinal bioavailability, because of the absence of first-pass metabolism of these drugs in the lung. There is also evidence to show that the greater glucocorticoid potency of fluticasone propionate translates directly into greater systemic bioactivity, but not into enhanced efficacy, at doses above 1 mg daily. The use of efficient delivery systems, such as the reservoir dry powder inhaler device, may not only improve control of asthma and compliance with therapy, but may also allow dose reduction ('step-down' therapy) and hence may possibly reduce overall prescribing costs in the long term.