Assessment End Points for Inhaled Drug Delivery

There is no "best" outcome or "gold standard" in the assessment of inhaled drug delivery. All levels of inquiry are important in development of drug formulations and delivery devices, and culminate in optimal therapy for the patient. Some advantages and disadvantages of each approach are summarized in Table 3. Each level forms a framework for the next step in the process, with in vitro leading to in vivo, followed by clinical trials. For optimal design, predictions and measurements of inhaled drug delivery should be done prior to large, expensive clinical trials. Bench testing with in vitro models is essential to document the performance of the delivery device/drug combination, whereas in vivo studies examine the behavior of the aerosol in human subjects. Both scintigraphy and pharmacokinetic/pharmacodynamic studies can add insights into the relationship between drug delivery and clinical efficacy and toxicity.