Getting to Know Your Inhalers

There are many different inhalers used to deliver inhaled pharmaceutical aerosols (IPAs). Most people have seen someone using a "puffer" to alleviate asthma and sinusitis symptoms. Inahalers have been a very popular choice of treatment for patients with respiratory symptoms because they deliver fast relief and most of these inhalers are very easy to use.

Inhalers disperse medications in very small particles, making them great tools for reaching the insides of the sinuses and nose. In a study by Christopher Hilton, M.D., et al about the differential deposition of aerosols in the maxillary sinus by particle size, it was concluded that particle size is a major factor in the distribution and affectivity of medication given to a patient. The smaller the size, the better it helps in improving one’s respiratory condition such as chronic sinusitis.

The following are the more common types of inhalers available:

I. pMDIs

The technical term for such puffers is "pressurized metered dose inhaler" (pMDI or MDI) or "propellant metered dose inhaler."

pMDIs are the most commonly used inhaler worldwide. The aerosol is created when a valve is opened, allowing liquid propellant to spray out of a canister. The drug is usually contained in small particles (usually a few millionths of a meter in diameter) suspended in the liquid propellant, but in some formulations the drug is dissolved in the propellant. In either case, the propellant evaporates rapidly as the aerosol leaves the device, resulting in small drug particles that are inhaled.

II. Nebulizers

Although pMDIs are the most common type of modern day inhalers, they are not the oldest. Nebulizers have been around in one form or another for more than a century. Nebulizers produce a mist of drug-containing water droplets for inhalation.

Jet nebulizers are more common due to their lower cost, and use a source of pressurized air to blast a stream of air through a drug-containing water reservoir, producing droplets in a complex process involving a viscosity-induced surface instability that leads to nonlinear phenomena in which surface tension and droplet breakup on baffles play a role.

In contrast, electronic nebulizers produce droplets by mechanical vibration of a plate or mesh.

In either type of nebulizer, the drug is usually contained in solution in the water in the nebulizer. However, for some formulations the drug is contained in small particles suspended in the water, which are then contained as particles suspended inside the droplets being produced.

III. DPI

Another major type of inhaler is the dry powder inhaler(DPI). In DPIs the aerosol is a powder, contained within the device until it is inhaled. In many DPIs the drug is mixed with much larger sugar particles that are typically 50-100 micrometers in diameter. The much smaller drug particles attach to these excipient particles. The increased aerodynamic forces on the lactose/drug agglomerates improve entrainment of the small drug particles upon inhalation, in addition to allowing easier filling of small individual powder doses. Upon inhalation, the powder is broken up into its constituent particles with the aid of turbulence and/or mechanical devices such as screens or spinning surfaces on which particle agglomerates impact, releasing the small, individual drug powder particles into the air to be inhaled into the lung. The sugar particles are intended to be left behind in the device and in the mouth-throat.

To read the complete study on Differential Deposition of Aerosols in the Maxillary Sinus, please refer to http://www.sinusdynamics.com/differential-deposition-of-aerosols.html.

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