Asthma & Bronchodilators
Wheezing and difficult breathing in asthma are caused by narrowing of the air passageways—called bronchial tubes—of the lungs. One of the important causes of narrowing of the bronchial tubes is contraction of the muscles that are present in a ring around these tubes. In asthma, contraction of these muscles causes the bronchial tubes to become more narrow than normal.
Medications to Open Bronchial Tubes Wider
Bronchodilators are medications that cause the bronchial muscles to relax and, as a result, the bronchial tubes to open wider or dilate. When these muscles relax, the bronchial tubes can usually open fully again and breathing can become normal. We say “usually” because sometimes the bronchial tubes themselves are swollen and filled with mucus. If this swelling and plugging of the bronchial tubes is present, then a bronchodilating medication will only bring partial relief of asthma symptoms. In this case, even when the bronchial muscles are made to relax, the bronchial tubes remain partially narrowed and blocked.
In this pamphlet we discuss the various types of bronchodilating medications and their effects in asthma. First, to understand better how bronchodilators work, it is necessary to explore a little more about the bronchial muscles.
Bronchial Muscles are “Involuntary” Muscles
Muscles in our body over which we have conscious control are called “voluntary” muscles. If we want to, we can make our arms and legs move by causing contraction of the voluntary muscles in our arms and legs. On the other hand, many muscles in our body are controlled unconsciously. For instance, we have no conscious control over the beating of our heart muscle or the contractions of our stomach muscles. Like these muscles, the muscles around our bronchial tubes are “involuntary” muscles; they are under the control of our nervous system but are not controlled by the thinking parts of our brain.
Contraction of the Bronchial Muscles
Although the bronchial muscles do not work quite as fast as the voluntary muscles, they can squeeze or contract over approximatley a minute or two. Anyone with asthma who has experienced the rapid onset of chest tightness and labored breathing and wheezing—for instance, after running on a cold day or being exposed to smoke or strong fumes—knows the effect of bronchial muscle contraction and the rapidity with which it can develop. The good news here is that relaxation of these bronchial muscles can occur equally rapidly, over a period of just a few minutes, allowing the bronchial tubes to widen again and breathing to occur freely.
Bronchodilators and Exercise
If asthma symptoms develop after running on a cold day, the bronchial muscles, left unstimulated, will usually gradually relax on their own over approximately an hour or less and the symptoms of asthma will go away. Bronchodilators are useful medications because they speed this process of relaxation of the bronchial muscles and can sometimes be used to prevent or block the contraction of the bronchial muscles in the first place. You may have made these observations yourself. If you use your bronchodilator medication before exercising, you can avoid developing wheezing, cough, and shortness of breath. If you use your bronchodilator after exercising has caused symptoms, the medication generally relieves the symptoms within 5 minutes or less. And if you simply stop exercising and wait, you gradually get better again over the next 30-60 minutes or so.
Choices Among Bronchodilators
Bronchodilators can be taken in different forms. They can be breathed in as a spray or mist, swallowed as a tablet or capsule, and sometimes given as an injection or intravenous medication (through a needle in a blood vessel). The advantage of inhaling bronchodilators is that the medication goes rapidly and directly to the bronchial muscles; it does not have to pass through the stomach and blood vessels to get there. As a result, inhaled bronchodilators are usually stronger and have fewer unpleasant side effects than swallowed bronchodilators.
Like most medicines, bronchodilators can be grouped into general “families” or groups of medicines based on their chemical properties. The most widely used family of bronchodilators at the present time is called the beta-adrenergic agonists or beta agonists for short. Beta, the Greek letter “B,” simply distinguishes this family of medications from a different group labeled with an “A.” Agonists describe medications that stimulate something, and in this case refer to stimulation of the bronchial muscles to relax. Adrenergic refers to the adrenaline-like properties of these medicines. Examples of beta-agonist bronchodilators that can be inhaled are familiar to you: they include the generic names albuterol, metaproterenol, pirbuterol, terbutaline, formoterol, and salmeterol and the brand names Ventolin®, Proventil®, Alupent®, Metaprel®, Maxair®, Brethaire®, Foradil® and Serevent®.
Some of the beta-agonist bronchodilators are also available in tablet form. Although it often is more convenient to swallow a tablet than to use an inhaler, these same medications when taken by mouth generally are not as strong and tend to have more unpleasant side effects than when breathed in. The most common side effects of the beta agonists are raciness, jitteriness, heart pounding, tremulousness, and a nervous feeling. The beta agonists do not cause high blood pressure.
Theophylline Family of Bronchodilators
Another family of bronchodilator medications is only available to swallow or inject intravenously: the theophylline family. The special advantage of this group of bronchodilators is that with some of them the bronchodilator stays in the blood for 12-24 hours after taking the tablet or capsule, making possible use once or twice a day with continuous benefit throughout the day. There are several disadvantages to theophylline bronchodilators, however. They are not as strong as the beta agonists; they often have unpleasant side effects, especially stomach discomfort, loose bowels, sleeplessness, and jitteriness; and occasionally they can have dangerous effects (abnormal heart rhythms and seizures) when excessive amounts of theophylline get into the blood (an overdose). The amount of theophylline bronchodilator in the blood can be measured with a blood test, referred to as the “theophylline level.” Many brand name examples of theophylline exist, including Theodur®, Unidur®, Uniphyl®, Slophylline®, Slo-Bid®, and others. Theophylline is the generic name for all of these medicines.
Anticholinergic Bronchodilators (Used toTreat Emphysema and Chronic Bronchitis)
One other family of bronchodilators is used in patients with emphysema and chronic bronchitis but is not usually recommended in asthma. The inhaled bronchodilator ipratropium (brand name, Atrovent®) is not as effective in asthma as are the beta agonist bronchodilators; it is weaker and takes longer to begin to work. Only in certain special circumstances would we recommend this type of bronchodilator for persons with asthma.
What Bronchodilators Do Not Do
It is important to remember that not all of asthma is corrected by causing the bronchial muscles to relax. Swelling of the bronchial tubes and their blockage with mucus—the aspects of asthma that we refer to as “inflammation,” do not go away when bronchial muscles relax. If you use your bronchodilator medication and don’t obtain relief of your asthma symptoms, the problem may not be with the bronchodilator. Bronchodilators cannot fix inflamed bronchial tubes. Other medications are available to treat this other aspect of asthma, the anti-inflammatory medications. Remember: if you are having difficulty with your asthma that is not fixed with use of your bronchodilator, other types of treatments are available and are likely to be needed. Your doctor can prescribe them for you and help guide you in how to use them.