Powder inhalation systems

Abstract

Inhalation of bronchodilators and corticosteroids is the mainstay treatment for patients with obstructive lung diseases. Many dry powder inhaler devices and drug combinations are now available, and competing promotional claims can confuse both prescribers and patients. The appropriate dose of a given drug may be different for a pressurized metered dose inhaler (pMDI) and a dry powder inhaler (DPI). DPIs create aerosols by drawing air through an aliquot of dry powder. The powder contains either micronized (< 5 micro m in diameter) drug particles bound into loose aggregates, or micronized drug particles that are loosely bound to large (> 30 micro m in diameter) lactose or glucose particles. Usually, the drug particles are bound to carrier particles and are stripped form the carrier particles by the energy provided by the patientacute;s inhalation. The release of respirable particles of the drug requires inspiration at relatively high flow rates (30 - 120 L/min). Other important factors influencing aerosol generation and lung deposition are device design (resistance to airflow) and environmental conditions (humidity, temperature). Preferably, patients should employ only one type of aerosol-generating device for inhalation therapy. The technique of use varies among devices, and repeated instruction is highly advisable, to ensure that the patient uses the device appropriately. At present, DPIs are recommended for prophylactic and maintenance therapy in patients with asthma and chronic obstructive pulmonary disease, but not for patients with acute severe bronchoconstriction or children less than 5 years of age.