Respiratory Drug Delivery

In respiratory drug delivery the lungs or the nose are exploited as absorption sites for the administration of systemically-acting drugs. Inhalation dosage forms allow to introduce the formulation inside the airways by generating a respirable aerosol. These dosage forms are unique since together the formulation and delivery device constitute the inhalation product, both affecting the bioavailability of the inhaled drug. The biopharmaceutical constraints of orally administered drug products can be less stringent for preparations for inhalation, which introduce though other issues, i.e., delivery and lung deposition. Deposition anticipates the dissolution and permeation processes and depends on the formulation and the device that must guarantee that the right amount of drug is delivered and inhaled. The main quality requirement of an inhalation product is its respirability, determined by the capacity of the drug formulation to be aerosolized, inhaled and deposited into the lung. This depends essentially on the aerodynamic diameter of the particle or droplet composing the aerosol. Here, the main types of pulmonary inhalers are illustrated, focusing on the aerodynamic behavior of the generated aerosol. Much attention is given to metered dose inhalers (MDIs) and their recent change of propellants and on dry powder inhalers (DPI) with their advanced solution for dosing and aerosolizing fine powders for systemic drug delivery. Finally, nasal drug delivery is considered with respect to the variables affecting the efficiency of the administration.