Achieving Optimal Particle Size Distribution In Inhalation Therapy

By Bob Bruno, President and COO, Microfluidics

Inhalation therapy has proven to be an effective method of administering a number of pharmaceuticals for more than a century. However, achieving the optimal particle size for a treatment with particular pharmaceutical formulations has been a troublesome task. This article addresses many of the concerns that medical device manufacturers and their pharmaceutical partners have when attempting to achieve the correct particle size for an inhalation device.

A principal benefit of inhalation therapy is the rapid onset of action, especially when compared to perorally-ingested medicine (oral dosages). The fast medicinal action produced by inhalation delivery results from the large absorption area of the lung. For locally acting drugs, the onset of action is immediate. Systemically-active inhaled drugs reach the blood stream quickly, within seconds. Rapid onset of action is especially important for rescue medications (i.e., asthma products), as well as pain medication and time-sensitive therapies, such as insulin. Patients cannot always afford to wait the 15 minutes or longer it often takes for a tablet to make its way though the gastrointestinal tract.

Avoiding the GI tract offers, through inhalation therapy, other advantages. Unlike perorally-ingested medicine, inhaled drugs are not subjected to the first-pass metabolism effect that significantly reduces bioavailability. After a drug is swallowed, it is absorbed by the digestive system. The absorbed drug is then carried through the portal vein into the liver. Some drugs are so extensively metabolized by the liver that only a small amount of unaltered drug may enter systemic circulation. Further, stomach contents and variable absorption levels among patients add to the variability of bioavailability of the drug.