Asthma Medicines

In an acute attack the fastest means of getting this medication to the bronchial tubes is by inhalation. This can be achieved in minutes by inhaling medicated spray administered by a metered-dose inhaler or powder delivered by a simple handheld device. A medicated mist generated by a nebulizer can also be used for inhalation.

What Is an Asthma Aerosol?

An asthma aerosol is a mixture of a liquid medication suspended in a gas that can be inhaled. Aerosols differ in the size of the spray or mist particles that are inhaled. Particle size is important since large particles are not likely to reach the bronchial tubes and may land in the mouth or throat. Examples of asthma aerosols are sprays from metered-dose inhalers (MDIs) and nebulizers. The goal of aerosol therapy is inhalation of active medication with penetration into the bronchial tubes.

Metered-Dose Inhalers

Metered-dose inhalers contain medication in aerosol form. These devices were first introduced in 1956 and have become widely used for asthma and rhinitis. MDIs consist of a canister of medication and an actuator with a mouthpiece. The actuator is the outer shell in which the canister “sits.” In the canister, medication is suspended in a mixture of a liquid propellant gas and preservatives. The current propellant used in most MDIs is a mixture of freon gases called chlorofluorocarbons.

When the canister is pressed into the actuator, the mixture of medication and propellant passes through a valve. The release of the contents under pressure transforms the liquid mixture into a spray that can be inhaled.

The metered-dose inhaler is the most common means of administration of the B-adrenergic agonists. It is a compact and portable device which dispenses a certain amount of medication rapidly. Coordination between hand activation of the MDI and breathing must exist for the medication to be properly delivered. Metered-dose inhalers come in many shapes and sizes.

Although the metered-dose inhaler is in general a safe device, it should be noted that a small number of patients may have adverse reactions to the propellants. This reaction may produce a worsening of asthma symptoms instead of the expected improvement after use of the MDI. Patients must also be careful to keep the mouthpiece of the metered-dose inhaler closed when not in use and free of foreign objects. Many patients have inadvertently aspirated foreign objects such as coins which slipped into the open mouthpiece and were then inhaled. MDIs are frequently kept in a pocket or purse where such foreign objects are usually found, so it is best to carefully check the MDI before its use.

A thirty-two-year-old man under my care for bronchial asthma called me in distress one night stating that “something went wrong when I sprayed.” He had been in the habit of keeping his uncovered MDI in his pocket and while shopping had placed loose change in the same pocket.

After dinner he had used his MDI and felt “something go in.” An x-ray in the emergency room showed a dime lodged in his windpipe. A procedure called bronchoscopy was required to remove it. The patient was released the next day with an MDI that he had carefully capped.

Nebulizer

A nebulizer may also be used to rapidly deliver aerosol medication containing B-adrenergic agonists. This device, which is commonly used in an emergency room setting, is basically a simple system that allows rapidly flowing air or oxygen to be bubbled through a solution containing the drug. This system produces a vapor that the patient inhales. Nebulizers differ in terms of the size of mist particles they produce. Of note, the nebulizer does not require the coordination between hand and breathing necessary for MDI use.

Nebulizer delivery of a B-agonist is preferred in emergency settings due to the greater quantity of drug that can be delivered. This has been estimated to be approximately from four to ten times the amount of medication delivered by two puffs from a metered-dose inhaler. The greater quantity of drug delivered by the nebulizer method may also result in greater side effects (tremors, rapid heartbeat, muscle cramps, nervousness) than those noted after metered-dose inhalation. In an emergency setting the beneficial effect of opening the bronchial tubes usually out-weighs any adverse side effects.

Nebulizers may be obtained for the home but this should not be necessary for most asthma patients. In view of the adverse effects and increased dosage noted above, a home nebulizer should only be prescribed for the most severely afflicted patients with asthma that cannot be controlled with metered-dose sprays or powder. These devices are much more expensive and cumbersome than MDIs, although portable units are available.

One advantage of the nebulizer may be its ability to combine more than one drug in solution given as one treatment. It should be noted, however, that metered-dose inhalers with more than one medication are likely to be available soon.

Metered-Dose Inhaler versus Nebulizer Delivery

A number of studies have compared the effectiveness of a B-agonist delivered by a metered-dose inhaler with a spacer attachment and the same drug delivered by a nebulizer. These studies have shown little or no difference in effectiveness between the two delivery systems. One explanation is that with a metered-dose spray the patient takes a deep breath to deliver medication to the bronchial tubes, while with a nebulizer the patient breathes normally. The deep breath may actually be advantageous to the delivery of medication to smaller bronchial tubes. During a severe attack, however, it may be difficult for patients to actively inhale deeply enough. wnile routine use of a nebulizer for stable asthma should be discouraged, there remains a definite place for nebulizer delivery of medication in patients with severe disease and in an emergency.

Nebulizers also require more maintenance and cleaning than do MDIs. There is a greater risk of contamination with nebulizers and patients must follow a proper cleaning routine.

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The B-agonists were developed in the 1940s, with isoproterenol the first of the class. Like epinephrine (adrenaline) this agent has both beta-1 and beta-2 effects. Isoetharine was one of the first”selective”B2-adrenergic agonists introduced in the United States and it was followed by metaproterenol. With the development of selective B2-adrenergic agonists there is no place for the use of nonselective agents that have significant stimulatory effects on the heart and circulation. Further research has produced more potent and longer-acting selective agents.

For the Acute Asthmatic Attack: Short-Acting Agent

Several selective B2-adrenergic agonists are available for use. These agents are available as aerosol sprays delivered by metered-dose inhalers (MDIs), aerosol solution to be delivered by nebulization, dry powders for inhalation (DPI), short and long-acting tablets, and as syrups flavored for children. In the acute asthmatic attack the treatment of choice for prompt relief of symptoms is the administration of a short-acting B2-adrenergic agonist. B2-adrenergic agonists (albuterol, metaproterenol, pirbuterol, terbutaline, fenoterol, and bitolterol) have a rapid onset of action (within minutes) with a duration of action of four to six hours. The recommended dosage is two puffs every six hours as needed. These medications differ in potency as well as how fast they begin to work and when their peak effect is reached. There are also differences in how long the effect of the drug lasts. Fenoterol has never been made available in the United States. Its extremely rapid onset of action may have contributed to its overuse and it has been implicated in cases of fatal asthma in New Zealand. Table 1 lists the B2-agonists by generic and brand name as well as the types of preparations that are available.

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