Breath of Fresh Air: Feature Articles

In 1956 the first metered-dose inhaler was developed by a scientist working at 3M Pharmaceuticals. Prior to that time, inhaled medications were administered by bulb nebulizers, water pipes, and even cigarettes (filled with dried leaves of stramonium)! The metered-dose inhaler (MDI) ensured that exactly the same amount of medication (a "metered dose") was administered with each actuation of the inhaler. More than forty years later, these simple, pocket- and purse-sized devices remain the mainstay for administering many anti-asthma medications, both quick-relievers and preventative controllers.

"Simple" is perhaps not fully accurate in describing the use of MDIs. Proper use requires rather precise coordination in depressing the canister and inhaling the medication. The manufacturers can ensure that exactly the same amount of medication leaves the mouthpiece of the MDI with each "puff," but they cannot control how much of the medication actually makes its way to the bronchial tubes inside the lungs, where the medication is meant to have its effect. In patient surveys, errors in the proper use of MDIs were very common, and understandably so.

Metered-dose inhalers replaced bulb nebulizers, water pipes, and medication-filled cigarettes!

The inhalers deliver a spray that leaves the metering nozzle at approximately 65 miles per hour. We are asked then to breathe in as soon as the spray is released (or even just before), breathe in slowly through our mouth (too fast, and much of the medicine is deposited on the back of the throat), and hold our breath for 5-10 seconds thereafter (so as not to lose a lot of medicine in an immediate exhalation). Some physicians ask that we breathe out first before squeezing the MDI and beginning to breathe in; others feel that that is an unnecessary complication to the process. Some physicians suggest that we put the mouthpiece of the inhaler directly into our mouth between lips and teeth; others recommend that we hold our mouth wide open and aim the inhaler from about one inch away (to allow the spray to slow before it enters our mouth).

Even at our best, with perfect coordination and timing, only about 15-20% of the medicine that leaves the MDI actually settles onto our bronchial tubes. The remainder in part is lost into the air and, mostly, settles in our mouth and upper part of the breathing passageway. Clearly, this system for delivering asthma treatments has room for improvement.

Metered-dose inhalers are tricky to use properly.

In the last few years, two new types of inhalers have become available that are designed to improve medication delivery to the airways. They address the problem of proper timing and coordination, at least in part, by not releasing medication until one starts to breathe in. Neither system begins with depressing a metal canister in its plastic holder.

Two new types of inhalers have become available:

One system is called a breath-actuated device. A pressurized spray of medication is released (as from an MDI) only when the spring-loaded device detects the pull of air flowing into your lungs. For each dose, one cocks up the lever at the top of the inhaler system. With lips tight around the mouthpiece, a breath in opens a valve and releases the puff of medication. A small audible "click" signals the release of medicine. Only one breath-actuated inhaler is currently on the market. It is called an Autohaler®, and it is marketed with the quick-reliever bronchodilator, pirbuterol (Maxair® Autohaler®).

The other system does not involve a pressurized aerosol of medicine at all. Instead, the medicine is prepared as a very fine, dry powder. An aerosol is generated when a forceful breath in pulls the medicine through a spiral chamber and swirls it into the air that is breathed. The precise amount of medication is set for each dose either by rotating a wheel that releases medicine from a larger reservoir or by pushing a lever that opens a single-dose "blister pack."

Some readers may remember the Spinhaler® device that was at one time widely used to deliver cromolyn (Intal®). It was an early form of a dry-powder inhaler with the following two disadvantages. For each dose a separate capsule had to be introduced into the delivery device, and the powder was coarse and somewhat irritating, much of it settling on one's tongue and throat. The newer generation of dry-powder inhalers have overcome these shortcomings. They contain at least one month's supply of medication in each device, and the powdered aerosol that is released is extremely fine and barely detectable. Two currently available dry-powder inhalers are the Turbuhaler® used to deliver an inhaled steroid, budesonide (Pulmicort®), and the Diskus® used to deliver the long-acting beta-agonist, salmeterol (Serevent®). Other dry-powder inhalers will likely soon be made available that will deliver the bronchodilator, albuterol, and inhaled corticosteroids other than budesonide.