Asthma Medicines

The B-adrenergic agonists available in tablet or elixir form are not for emergency use since they have slow onsets of action (up to one hour). Albuterol, terbutaline, and metaproterenol are available as oral medications. Since they are absorbed into the bloodstream in greater quantity than the inhaled form, there are greater chances of side effects. These include tremors, muscle cramps, nervousness, insomnia, and palpitations. The long-acting oral preparations of albuterol have proved useful for patients with nocturnal asthma, although the long-acting aerosol sprays that have become available also have been effective in this setting. Those patients who have difficulty using a metered-dose inhaler may benefit from the oral preparations.

Another potential advantage of oral preparations is that the medication carried in the blood may reach small bronchial tubes that may not have been reached by inhalation. These small airways are often inflamed and swollen in moderate and severe asthma and receive only a relatively small percentage of the medication inhaled. In addition, there may be thick mucus “plugs” that block the air passages. Aerosol medication may therefore be primarily distributed to the larger, more open passages which receive greater airflow on inhalation. It is conceivable, however, that medication deposited in these larger passages may be absorbed into blood vessels and reach the blood circulation, thereby eventually reaching the smaller airways.

In the asthmatic patient who does not appear to respond fully to aerosol medication, trial with an oral preparation is indicated. Peak flows or spirometry may be performed after a suitable trial of one to two weeks. If flow rates have increased and symptoms have diminished, then the oral preparation of the B2-adrenergic agonist may be used in conjunction with the aerosol. A drawback to this approach will be the greater likelihood of adverse effects from the increased absorption of the B-agonist. Of note, however, is that tolerance to these effects often develops after several days of use. Unfortunately, the elderly population with asthma may be adversely affected more than younger patients. Tremors may be especially severe in older patients. These patients are also more likely to have preexisting cardiac conditions that may increase the risk of adverse effects such as rapid or irregular heart rhythms.

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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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