Usmani concludes that: “Studies now show that treating the peripheral airways with smaller drug particle aerosols certainly achieve comparable efficacy (and some studies show superiority) compared with large particles, a reduction in the daily inhaled corticosteroid dose, and greater asthma control and quality of life in real-life studies.”
In terms of ensuring that very fine particles are retained in the lung rather than exhaled, there have been some interesting developments here too. A recent study by Poli & Lipworth, for example, demonstrated that the exhaled fraction/lung deposition ratio is independent of the median mass aerodynamic diameter (MMAD) of an inhaled product, which suggests that targeting a smaller particle size will not lead to increased drug loss via exhalation.
Taking a different approach, experimental work by Hoppentocht showed that better targeting and retention in the peripheral lung is achievable by making sub-micron drug formulations hygroscopic so that they grow in the respiratory tract. Delivering such particles resulted in high deposition fractions in the lower trachea bronchial tree.
Q: Why would flow rate independence be helpful?
A: The effect of flow rate on drug delivery is important for two reasons. Patients inevitably have different inspiratory profiles as the breathing patterns of patients are influenced by physical size and strength, as well as health. Geriatric and pediatric patients, or those with severely compromised respiratory capacity, are likely to impose a lower flow rate and inhale a smaller total volume than a healthy adult.
